Selective laser sintering (SLS) 3D printing is considered one of the most reliable and productive forms of additive manufacturing.[1] Recently, advances in hardware are improving SLS printing even further, enabling even better surface finish quality and achievable level of fine details.&nbsp;At <a href="https://sintratec.com/" target="_blank" rel="noopener noreferrer">Sintratec</a>, a Swiss maker of professional SLS systems, these advances are in the form of high-precision lasers with spot sizes significantly smaller than other entry-level SLS systems. This has enabled Sintratec to achieve unparalleled print resolutions and feature sizes on its SLS platforms. In this article, we look at what laser spot size is, how it influences print resolution, and how Sintratec’s technologies are unlocking new opportunities for SLS users.<h2 dir="ltr">The Science of Laser Spot Size</h2>Selective Laser Sintering is an additive manufacturing technique that fabricates parts by sintering powdered material using a laser. The process begins by depositing a thin layer of polymer powder onto a build platform. A high-powered laser then selectively scans the surface, melting and fusing the powder according to the cross-sectional geometry of the part being built. On the completion of one print layer, the build platform descends incrementally, and a new layer of powder is spread across the surface, repeating the sintering process. This layer-by-layer approach continues until the part is complete. [2]While there are different types of lasers that can be used in the SLS process, one of the most common is Fiber Lasers. These lasers generate light through diodes that pump energy into a fiber optic cable doped with rare-earth elements such as ytterbium. The resulting light typically has a wavelength of about 1,060 nm, which offers high absorption rates in metals and certain polymers. This characteristic makes fiber lasers highly effective for the precision melting of polymer and metal powders. Advantages of fiber lasers in SLS include their excellent beam quality, energy efficiency, and minimal maintenance requirements. [3]When evaluating laser performance in SLS printing, laser spot size is one of the most important specifications. In short, laser spot size (also known as laser beam diameter) is defined as the smallest diameter that a laser can be focused to with a lens. One major reason why laser spot size is so valuable is because it directly influences the laser energy density, which determines the precision and quality of the sintered parts by affecting the melt pool size, depth of penetration into the powder bed, and overall resolution of the final product. Laser energy density is defined as [4]<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzEzOTU3Mjc2OTk1LVNjcmVlbnNob3QgMjAyNC0wNC0yNCAxMzE0MTYucG5nIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 100%px;" class="fr-fic fr-dib">&nbsp;Where:Eₛ is the laser energy density (J/cm^2)P is the incident laser power (Watts)v is the laser scan speed (cm/s)δ&nbsp;is the laser beam spot size (cm)The laser spot size itself can be defined and calculated in several different ways, but, in the case of SLS printers, spot size is generally defined by the full width at half-maximum (FWHM). Essentially, FWHM quantifies the beam's spread or divergence by measuring the distance between the two points on the intensity profile (a plot of light intensity versus position) at which the intensity falls to half of its peak value. [5]There are many variables that impact the laser beam spot size. Assuming an ideal Gaussian beam, it’s well-defined that the beam width varies as it propagates along its axis. Therefore, the spot size at the focal length is determined by the focal length itself, the smallest radius of the Gaussian beam (i.e., beam waist), and the beam’s wavelength. Based on this, the spot size is mathematically defined as [6]<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzEzOTU3NTExMjE0LVNjcmVlbnNob3QgMjAyNC0wNC0yNCAxMzE4MjMucG5nIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 100%px;" class="fr-fic fr-dib">Where:f is the focal length.Wf&nbsp;is the beam radius focal length (i.e., spot size)λ is the laser wavelengthw₀ is the beam waist<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1714132304695-o.jpg" style="width: 100%px;" class="fr-fic fr-dib">Figure 1: The propagation of a laser along its axis.Ultimately, the laser spot size is an important factor that influences the resolution of printed components as well as properties like density, strength, and minimum feature size. In essence, the degree of detail an SLS 3D printer can achieve is determined by the laser spot size, and the minimum feature size typically corresponds to the laser spot size.<h2 dir="ltr">Impact of Laser Spot Size on Print Quality</h2>When we talk specifically about resolution in 3D printing, there are two types of resolution to consider: the Z resolution and XY resolution. Z resolution is the vertical resolution that is dependent on the layer thickness of the print (i.e. how finely the recoater can spread each new layer of powder material). XY resolution, for its part, refers to the horizontal resolution of the print and is influenced by both laser spot size and the precision of the laser’s movement. [7]A smaller laser spot size therefore directly corresponds to a higher XY print resolution and enables users to integrate very fine details and intricate features into their 3D prints. SLS 3D printers with smaller laser spots are also better equipped to print parts with superior surface finishes. Smaller laser spot sizes have been shown to decrease layer line height, resulting in less visible layer lines, smoother surfaces, and finer details in the printed objects. [8]&nbsp;Research has found that smaller laser spot sizes markedly enhance the geometrical accuracy of printed tracks. [9] One reason for this is that a small spot size affords precise control over the dimensions of the melt tracks, including their width, height, and depth. As part of this, smaller spot sizes minimize the heat-affected zone around the melt tracks, reducing thermal deformations and residual stresses that can compromise the mechanical integrity of the final product.&nbsp;Adjustments in laser power and scanning speed can significantly influence these parameters, enabling the creation of smoother surfaces and more defined track edges. Precise parameter control helps maintain stable melt pool dynamics, crucial for minimizing defects such as porosity and keyhole formation that degrade print quality.&nbsp;<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzEzOTU1ODQ4MTcxLTVfRXNjaGJhbF9TTFNDb21wb25lbnQuanBnIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 100%px;" class="fr-fic fr-dib"><h2 dir="ltr" id="isPasted">Sintratec’s Unique Selling Proposition (USP)</h2>Sintratec places an important emphasis on SLS printer laser spot size. The company’s machines boast some of the finest laser spot diameters and resolutions in the SLS 3D printing market today. The company’s newest fusion module for its All-Material Platform, the Sintratec S3, is equipped with a 30-watt fiber laser that is focused down to a spot size of just 145 μm. The S2, fitted with a 10-watt fiber laser, has the same laser spot size.&nbsp;Sintratec’s laser spot diameter is substantially smaller than many other SLS platforms on the market. This opens applications for its technology in industries like aerospace and electronics that require not only high throughput and process consistency but also high resolution and part accuracy. You can find a comparison of some leading SLS systems below:<table style="width: 100%;"><tbody><tr><td style="width: 50.0000%;">SLS 3D Printer </td><td style="width: 50.0000%;">Laser Spot Size (μm) </td></tr><tr><td style="width: 50.0000%;">Sintratec S3 and S2 </td><td style="width: 50.0000%;">145 μm [10] </td></tr><tr><td style="width: 50.0000%;">Prodways Promaker P1000 </td><td style="width: 50.0000%;">450 μm [11] </td></tr><tr><td style="width: 50.0000%;">Sinterit Lisa X </td><td style="width: 50.0000%;">650 μm [12] </td></tr><tr><td style="width: 50.0000%;">Formlabs Fuse 1 </td><td style="width: 50.0000%;">200 μm [13] </td></tr></tbody></table><h2 dir="ltr" id="isPasted">Real-World Applications and Benefits</h2>Adopters in various industries are already reaping the benefits of Sintratec’s high-resolution SLS solutions. Around the globe, its Swiss-made systems are leveraged by product developers, engineers, and researchers to create precise, functional prototypes that not only closely match the exact dimensions and shape of final parts, but also their mechanical properties. This application dramatically speeds up design validation and prototype testing, enabling users to move quickly and confidently into series production.<a href="https://sintratec.com/additive-manufacturing-sparks-innovation/" target="_blank">Kontakt-Simon SA</a>, a major manufacturer of electric installation equipment, has been using the Sintratec S2 since 2022 to create complex, high-precision prototypes for the electrical sector. The accuracy of Sintratec’s fiber laser system has been vital in this application because printed parts are used to validate geometries and assemblies before moving into full-scale production. The high-quality surface finish of Sintratec prints, as well as the ability to produce complex shapes with fine details, has been important to Kontakt-Simon, since electric housings and components must not only fit electrical components of varying geometries within them but also fit perfectly into larger assemblies. When asked about the main benefits of the S2, Thomas Wilk, Head of Kontakt-Simon’s technical department, listed “complex geometries, thin walls, high aesthetics and accuracy, great strength, and homogeneity in each axis of the part.”<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNzEzOTU2MDE1NjA3LTZfS29udGFrdFNpbW9uX1NMU0NvbXBvbmVudC5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 100%px;" class="fr-fic fr-dib">Swiss window maker <a href="https://sintratec.com/innovative-window-systems-with-sls-components/" target="_blank">Eschbal</a> has also integrated the Sintratec S2 for a number of end uses, including prototyping, tooling, and small series production parts. Like Kontakt-Simon, the company values the technology’s ability to print parts that closely match the properties of injection molded parts. “With the SLS process, we were especially impressed by the tolerances of up to 0.1 millimeters and the surface quality,” comments Michael Ebnöther, a member of Eschbal’s tech department. For tooling and end-use parts, mechanical properties are paramount. For example, Eschbal optimized a connector component through SLS 3D printing, reducing the weight of the final part by 33%.&nbsp;The case studies represent just a small fraction of the ways that Sintratec’s high-resolution 3D printers are being used. You can find more <a href="https://sintratec.com/stories/" target="_blank">customer stories</a> here.<h2 dir="ltr" id="isPasted">Conclusion</h2>Overall, laser spot size is an important piece of the SLS puzzle, influencing print properties like resolution. By focusing on precision through laser spot size, Sintratec has carved out a position for itself in the broader SLS market that caters to applications that require high print accuracy and fine details. In combination with SLS’ excellent throughput and consistency, the ability to achieve smaller features and ultimately better-quality prints takes the technology to another level.&nbsp;<h2 dir="ltr" id="isPasted">References</h2>1. Awad A, Fina F, Goyanes A, Gaisford S, Basit AW. 3D printing: Principles and pharmaceutical applications of selective laser sintering. Int J Pharm. 2020 Aug 30;586:119594. doi: 10.1016/j.ijpharm.2020.119594. Epub 2020 Jul 2. PMID: 32622811.2. David L. Bourell, Trevor J. Watt, David K. Leigh, Ben Fulcher, Performance Limitations in Polymer Laser Sintering,Physics Procedia, Volume 56, 2014, Pages 147-156, ISSN 1875-3892, https://doi.org/10.1016/j.phpro.2014.08.157.3. Liao, H, Le, MT, &amp; Long, DV. "Optimization on Selective Fiber Laser Sintering of Bimetallic Powder via Design of Experiments Method." Proceedings of the ASME/ISCIE 2012 International Symposium on Flexible Automation. ASME/ISCIE 2012 International Symposium on Flexible Automation. St. Louis, Missouri, USA. June 18–20, 2012. pp. 475-482. ASME. https://doi.org/10.1115/ISFA2012-72324. Lü, L., Fuh, J.Y.H., Wong, Y.S. (2001). Selective Laser Sintering. In: Laser-Induced Materials and Processes for Rapid Prototyping. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-1469-5_55. J. Chalupský, J. Krzywinski, L. Juha, V. Hájková, J. Cihelka, T. Burian, L. Vyšín, J. Gaudin, A. Gleeson, M. Jurek, A. Khorsand, D. Klinger, H. Wabnitz, R. Sobierajski, M. Störmer, K. Tiedtke, and S. Toleikis, "Spot size characterization of focused non-Gaussian X-ray laser beams," Opt. Express &nbsp;18, 27836-27845 (2010).6. Oz Livneh, Gadi Afek, and Nir Davidson, "Producing an efficient, collimated, and thin annular beam with a binary axicon," Appl. Opt. 57, 3205-3208 (2018)7. Anketa Jandyal, Ikshita Chaturvedi, Ishika Wazir, Ankush Raina, Mir Irfan Ul Haq, 3D printing – A review of processes, materials and applications in industry 4.0, Sustainable Operations and Computers, Volume 3, 2022, Pages 33-42, ISSN 2666 4127, <a href="https://doi.org/10.1016/j.susoc.2021.09.004" target="_blank">https://doi.org/10.1016/j.susoc.2021.09.004</a>.8. M. Launhardt, A. Wörz, A. Loderer, T. Laumer, D. Drummer, T. Hausotte, M. Schmidt, Detecting surface roughness on SLS parts with various measuring techniques, <a href="https://www.sciencedirect.com/science/article/abs/pii/S0142941816302057" target="_blank">https://www.sciencedirect.com/science/article/abs/pii/S0142941816302057</a>9. Vaglio E, De Monte T, Lanzutti A, Totis G, Sortino M, Fedrizzi L. Single tracks data obtained by selective laser melting of Ti6Al4V with a small laser spot diameter. Data Brief. 2020 Oct 22;33:106443. doi: 10.1016/j.dib.2020.106443. PMID: 33195769; PMCID: PMC7642809.10. <a href="https://sintratec.com/sls-3d-printer/amp/sintratec-s2/" target="_blank">https://sintratec.com/sls-3d-printer/amp/sintratec-s2/</a>11. <a href="https://www.prodways.com/wp-content/uploads/2021/09/ProMaker-P1000-Series-EN-V19.08.2021.pdf" target="_blank" data-lf-fd-inspected-kn9eq4roawkarlvp="true">https://www.prodways.com/wp-content/uploads/2021/09/ProMaker-P1000-Series-EN-V19.08.2021.pdf</a>12. https://www.3d-printer.com/3D_Printers/Sinterit_Printers/lisa-x13. https://formlabs.com/3d-printers/fuse-1/tech-specs/

Sintratec's high-precision lasers with smaller spot sizes allow for superior print resolution and finer details in SLS 3D printing.

Sintratec's Laser Spot Size The Key to Superior Print Resolution

Researchers from ITMO University have suggested a method of creating colored patterns with an affordable, domestically-produced laser. Compared to others, the new method makes it possible to create smaller separate patterns within a single bigger one, which are harder to forge. The technology, described in an article <a href="https://www.sciencedirect.com/science/article/pii/S0030399224001002?dgcid=coauthor" target="_blank" id="isPasted">published</a> in Optics and Laser Technology, will help prevent production of counterfeit glass products, such as medical vials and test tubes. &nbsp;Each material has a different nanorelief (irregularities, protrusions, or cavities on the surface) that affects its optical properties. For instance, one surface is better at harvesting and reflecting light, while another will have a limited emissivity. Each property has its own applications: materials with a light-harvesting nanorelief are used in solar cells, while reflective surfaces are used to create iridescent patterns that protect products from counterfeiting.Typically, photolithography is used to create ordered nanoreliefs. This method is reminiscent of using spray paint with a stencil: first, a template is made for the target image; then, it is recreated on a material by shining a laser through the template. However, photolithographs are expensive and require a lot of expendable materials, such as templates and photoresists (materials that react with laser radiation to register an image). Moreover, with this technique, it is impossible to change the image when writing is in progress – instead, that would require an all-new template.&nbsp;An alternative technique is direct writing with scanning laser beams. It doesn’t require expensive equipment or expendable materials, while also being capable of creating smaller structures, as if drawn by a thin brush. Researchers from ITMO’s <a href="https://en.itmo.ru/en/faculty/121/Institute_of_Laser_Technologies.htm/" target="_blank">Institute of Laser Technologies</a> have further improved this approach by introducing a method for generating laser-induced periodic surface structures (LIPSSs). The method can be used to distinguish, print, and combine even smaller nanostructures within the scanning area.&nbsp;<blockquote>“As the material has a rough surface, the laser radiation that reaches it diffracts and turns into an electromagnetic wave that spreads along the surface and interacts with incoming laser radiation. As a result, we get a nanorelief in the shape of a protective pattern. Imagine that laser radiation is a wide brush around 55-70 microns in size. And in this brush, different lines are created by filament, each just 0.7 micrometers in size – that’s 100 times thinner than a human hair. These filaments create tiny nanostructures inside the big structure,” explains&nbsp;Dmitry Sinev, an associate professor at the Institute of laser Technologies.</blockquote><img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1710979599139-ezgif-5-e850060be5.gif" style="width: 100%px;" class="fr-fic fr-dib">Protective trademarks formed via direct writing of laser-induced periodic surface structures. Video courtesy of Dmitry SinevThe new method works as follows: a titanium film is placed upon a glass substrate; then, the film is treated with a laser beam that creates a one-dimensional nanorelief in the shape of several lines. In order to make the geometry more complex and turn the image into a 2D one, the process of forming lines is repeated, with a new set of lines drawn across the first one. The final nanorelief is reminiscent of honeycombs and squares and can be seen in white light, like that from a flashlight.<blockquote>“Through repeated processing, the nanoreliefs took the thermophysical and mechanical properties of the substrate, as well as the optical properties of the film – this changed their interaction with polarized light, as well as refraction and light transmission spectra. Each nanostructure in a pattern shone with different colors of varying intensity based on the angle it was viewed from. Upon request from a customer, we can write any image with additional customization. For instance, we can create a nanostructure that will be brighter at a specific angle, and inform the customer about the configuration parameters. This way, only the customer will know the location of each element and thus will be able to identify the pattern,” adds&nbsp;Alexander Suvorov,, a second-year Master’s student at the Institute of Laser Technologies.</blockquote>According to the paper’s authors, the pattern can be made even more unique if several protective layers are combined in its production: for instance, the image can be writtenin 2D and in 1D.&nbsp;Next, the researchers are planning to use their method to make colorful trademarks that will prevent counterfeiting of medical vials, test tubes, and other products made from transparent materials. Currently, the novel method is capable of printing protective patterns with the resolution of 0.7 microns and the area of 1x1 millimeters in just 18 seconds. In the future, the researchers are planning to increase the writing speed and make the nanostructures smaller, in order to include more elements and make the image even harder to copy.This research project is&nbsp;<a href="https://rscf.ru/project/21-79-10241/" target="_blank">supported</a> by the Russian Science Foundation.

Protective trademarks formed via direct writing of laser-induced periodic surface structures. Photo by Dmitry Grigoryev / ITMO.NEWS

Researchers from ITMO University have suggested a method of creating colored patterns with an affordable, domestically-produced laser. Compared to others, the new method makes it possible to create smaller separate patterns within a single bigger one, which are harder to forge.

A Solution that Prevents Counterfeiting of Glass Products

What happens when you expose tellurite glass to femtosecond laser light? That’s the question that Gözden Torun at the Galatea Lab, in a collaboration with Tokyo Tech scientists, aimed to answer in her thesis work when she made the discovery that may one day turn windows into single material light-harvesting and sensing devices. The results are published in&nbsp;PR Applied.Interested in how the atoms in the tellurite glass would reorganize when exposed to fast pulses of high energy femtosecond laser light, the scientists stumbled upon&nbsp;<a href="https://doi.org/10.1002/adma.202210446" target="_blank" rel="noopener">the formation of nanoscale tellurium and tellurium oxide crystals</a>, both semiconducting materials etched into the glass, precisely where the glass had been exposed. That was the eureka moment for the scientists, since a semiconducting material exposed to daylight may lead to the generation of electricity.“Tellurium being semiconducting, based on this finding we wondered if it would be possible to write durable patterns on the tellurite glass surface that could reliably induce electricity when exposed to light, and the answer is yes,” explains Yves Bellouard who runs EPFL’s Galatea Laboratory. “An interesting twist to the technique is that no additional materials are needed in the process. All you need is tellurite glass and a femtosecond laser to make an active photoconductive material.”Using tellurite glass produced by colleagues at Tokyo Tech, the EPFL team brought their expertise in femtosecond laser technology to modify the glass and analyze the effect of the laser. After exposing a simple line pattern on the surface of a tellurite glass 1 cm in diameter, Torun found that it could generate a current when exposing it to UV light and the visible spectrum, and this, reliably for months.“It’s fantastic, we’re locally turning glass into a semiconductor using light,” says Yves Bellouard. “We’re essentially transforming materials into something else, perhaps approaching the dream of the alchemist!”.<hr>References<a href="https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.21.014008" target="_blank" rel="noopener">https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.21.014008</a>

A photoconductive circuit, where the circuit is directly patterned onto a glass surface with femtosecond laser light - 2024 EPFL / Lisa Ackermann - CC-BY-SA 4.0

EPFL physicists propose a novel way to create photoconductive circuits, where the circuit is directly patterned onto a glass surface with femtosecond laser light. The new technology may one day be useful for harvesting energy, while remaining transparent to light and using a single material.

Turning glass into a 'transparent' light-energy harvester

The progression of laser additive manufacturing — which involves 3D printing of metallic objects using powders and lasers — has often been hindered by unexpected defects. Traditional monitoring methods, such as thermal imaging and machine learning algorithms, have shown significant limitations. They often either overlook defects or misinterpret them, making precision manufacturing elusive and barring the technique from essential industries like aeronautics and automotive manufacturing. But what if it were possible to detect defects in real time based on the differences in the sound the printer makes during a flawless print and one with irregularities? Up until now, the prospect of detecting these defects this way was deemed unreliable. However, researchers at the Laboratory of Thermomechanical Metallurgy (<a href="https://www.epfl.ch/labs/lmtm/" target="_blank">LMTM</a>) at EPFL's School of Engineering have successfully challenged this assumption.<blockquote>There's been an ongoing debate regarding the viability and effectiveness of acoustic monitoring for laser-based additive manufacturing. Our research not only confirms its relevance but also underscores its advantage over traditional methods.<footer>Professor Roland Logé, Head of the Laboratory of Thermomechanical Metallurgy</footer></blockquote>Professor Roland Logé, the head of the laboratory, stated, "There's been an ongoing debate regarding the viability and effectiveness of acoustic monitoring for laser-based additive manufacturing. Our research not only confirms its relevance but also underscores its advantage over traditional methods."This research is of paramount importance to the industrial sector as it introduces a groundbreaking, yet cost-effective solution to monitor and improve the quality of products made through Laser Powder Bed Fusion (LPBF). Lead researcher, Dr. Milad Hamidi Nasab, remarked, "The synergy of synchrotron X-ray imaging with acoustic recording provides real-time insight into the LPBF process, facilitating the detection of defects that could jeopardize product integrity." In an era where industries continuously strive for efficiency, precision, and waste reduction, these innovations not only result in significant cost savings but also boost the dependability and security of manufactured products.<h2>How Does LPBF Manufacturing Work?</h2>LPBF is a cutting-edge method that's reshaping metal manufacturing. Essentially, it uses a high-intensity laser to meticulously melt minuscule metal powders, creating layer upon layer to produce detailed 3D metallic constructs. Think of LPBF as the metallic version of a conventional 3D printer, but with an added degree of sophistication. Rather than melted plastic, it employs a fine layer of microscopic metal powder, which can vary in size from the thickness of a human hair to a fine grain of salt (15–100 μm). The laser moves across this layer, melting specific patterns based on a digital blueprint. This technique enables the crafting of bespoke, complex parts like lattice structures or distinct geometries, with minimal excess. Nevertheless, this promising method isn't devoid of challenges.When the laser interacts with the metal powder, creating what is known as a melt pool, it fluctuates between liquid, vapor, and solid phases. Occasionally, due to variables such as the laser's angle or the presence of specific geometrical attributes of the powder or of the part, the process might falter. These instances, termed "inter-regime instabilities", can sometimes prompt shifts between two melting methods, known as "conduction" and "keyhole" regimes. During unstable keyhole regimes, when the molten powder pool delves deeper than intended, it can create pockets of porosity, culminating in structural flaws in the end product. To facilitate the measurement of the width and depth of the melt pool in X-ray images, the Image Analysis Hub of the EPFL Center for Imaging developed an approach that makes it easier to visualize small changes associated with the liquid metal and a tool for annotating the melt pool geometry.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1705050644241-5311e230.jpg" style="width: 300px;" class="fr-fic fr-dib">A graphic representation of the exeperimental setup for listening for printing defects - 2023 EPFL / Titouan Veuillet - CC-BY-SA 4.0<h2 id="isPasted">Detecting These Defects Using Sound</h2>In a joint venture with the Paul Scherrer Institute (PSI) and the Swiss Federal Laboratories for Materials Science and Technology (Empa), the EPFL team formulated an experimental design that melded operando X-ray imaging experiments with acoustic emission measurements. The experiments were conducted at the TOMCAT beamline of the Swiss Light Source at PSI, with the miniaturized LPBF printer developed in the group of Dr. Steven Van Petegem. The amalgamation with an ultra-sensitive microphone, positioned inside the printing chamber, pinpointed distinct shifts in the acoustic signal during regime transitions, thereby directly identifying defects during manufacturing.A pivotal moment in the research was the introduction of an adaptive filtering technique by signal processing expert Giulio Masinelli from Empa. "This filtering approach," Masinelli emphasized, " allows us to discern, with unparalleled clarity, the relationship between defects and the accompanying acoustic signature." Unlike typical machine learning algorithms, which excel at extracting patterns from statistical data, but are often tailored to specific scenarios, this approach provides broader insights on the physics of melting regimes, while offering superior temporal and spatial precision.With this research, EPFL contributes valuable insights to the field of laser additive manufacturing. The findings have significant implications for potential industrial applications, particularly in sectors like aerospace and precision engineering. Reinforcing Switzerland's reputation for meticulous craftsmanship and manufacturing accuracy, the study underscores the need for consistent manufacturing techniques. Furthermore, it suggests the potential for early detection and correction of defects, enhancing product quality. Professor Logé concludes, "This research paves the way for a better understanding and refinement of the manufacturing process, and will ultimately lead to higher product reliability in the long term."<hr>ReferencesHamidi Nasab, M., Masinelli, G., de Formanoir, C., Schlenger, L., Van Petegem, S., Esmaeilzadeh, R., Wasmer, K., Ganvir, A., Salminen, A., Aymanns, F., Marone, F., Pandiyan, V., Goel, S., &amp; Logé, R. (2023). Harmonizing Sound and Light: X-Ray Imaging Unveils Acoustic Signatures of Stochastic Inter-Regime Instabilities during Laser Melting . Nature Communications. DOI:&nbsp;<a href="https://www.nature.com/articles/s41467-023-43371-3" rel="noopener" target="_blank">10.1038/s41467-023-43371-3</a>

A graphic representation of the exeperimental setup for listening for printing defects - 2023 EPFL / Titouan Veuillet - CC-BY-SA 4.0

Researchers from EPFL have resolved a long-standing debate surrounding laser additive manufacturing processes with a pioneering approach to defect detection.

Laser additive manufacturing: listening for defects as they happen

In a study published Nov. 24 in&nbsp;<a href="https://www.nature.com/articles/s41467-023-43501-x" rel="nofollow" target="_blank">Nature Communications</a>,&nbsp;<a href="https://www.engineering.columbia.edu/" rel="nofollow" target="_blank">Columbia Engineering</a> researchers and collaborators at the&nbsp;<a href="https://www.mpsd.mpg.de/en" rel="nofollow" target="_blank">Max Planck Institute for the Structure and Dynamics of Matter</a> find that pairing laser light to crystal lattice vibrations can enhance the nonlinear optical properties of a layered 2D material. The finding could lead to new ways of using light to modify materials.Cecilia Chen, a Columbia Engineering PhD student and co-author of the paper,&nbsp;and her colleagues from the&nbsp;<a href="https://gaeta.apam.columbia.edu/" rel="nofollow" target="_blank">Quantum and Nonlinear Photonics group</a>, led by&nbsp;<a href="https://www.apam.columbia.edu/faculty/alex-gaeta" rel="nofollow" target="_blank">Alexander Gaeta</a>, David M. Rickey Professor of&nbsp;<a href="https://www.apam.columbia.edu/" rel="nofollow" target="_blank">Applied Physics</a> and Materials Science, used hexagonal boron nitride (hBN). A 2D material similar to graphene, hBN’s atoms are arranged in a honey-combed-shaped repeating pattern and can be peeled into thin layers with unique quantum properties. Chen noted that hBN is stable at room temperature, and its constituent elements—boron and nitrogen—are very light. That means they vibrate very quickly.Atomic vibrations occur in all materials above absolute zero. That movement can be quantized into quasiparticles called phonons with particular resonances; in hBN's case, the team was interested in the optical phonon mode corresponding to a wavelength of 7.3 μm, in the mid-infrared regime of the electromagnetic spectrum. While mid-IR wavelengths are considered short, and thus, high energy, in the picture of crystal vibrations, they are considered very long and low energy in most optics research, where the overwhelming majority of experiments and studies are performed in the visible to near-IR range of approximately 400 nm to 2 um.When they tuned their laser system to hBN’s frequency, 7.3 μm, Chen, along with Jared Ginsberg PhD’21 (now a data scientist at Bank of America) and postdoc Mehdi Jadidi (now a team lead at PsiQuantum), were able to coherently drive the resonance of the hBN crystal and generate new optical frequencies from the medium—a goal of nonlinear optics. Theoretical work led by&nbsp;<a href="https://www.mpsd.mpg.de/person/39745/2736" rel="nofollow" target="_blank">Angel Rubio’s group</a> at Max Planck helped the experimental team understand their results.Using commercially available, table-top mid-infrared lasers, they explored the phonon-mediated four-wave mixing around even harmonic orders. The crystal could withstand up to 10% atomic displacement without damage. They also observed a 30-fold increase in third-harmonic generation.“We’re excited to show that amplifying the natural phonon motion with laser driving can enhance nonlinear optical effects and generate new frequencies,” said Chen. In future work, the team plans to explore how to modify hBN and materials like it using light.

The Gaeta lab used near-infrared light to drive particles in a crystal of hexagonal boron nitride, generating new optical frequencies. Credit: 420494 from Pixabay

Columbia Engineers pair vibrating particles, called phonons, with particles of light, called photons, to enhance the nonlinear optical properties of hexagonal boron nitride. The finding could lead to new ways of using light to modify materials. Learn more.

Laser-driving a 2D Material

The team at EPFL’s <a href="https://phosl.epfl.ch/" target="_blank">Photonic Systems Laboratory</a> (PHOSL) has developed a chip-scale laser source that enhances the performance of semiconductor lasers while enabling the generation of shorter wavelengths. This pioneering work, led by Professor Camille Brès and postdoctoral researcher Marco Clementi from EPFL’s School of Engineering represents a significant advance in the field of photonics, with implications for telecommunications, metrology, and other high-precision applications.The study, published in the journal Light: Science &amp; Applications, reveals how the PHOSL researchers, in collaboration with the <a href="https://www.epfl.ch/labs/k-lab/" target="_blank">Laboratory of Photonics and Quantum Measurements</a>, have successfully integrated semiconductor lasers with silicon nitride photonic circuits containing microresonators. This integration results in a hybrid device capable of emitting highly uniform and precise light in both near-infrared and visible ranges, filling a technological gap that has long challenged the industry."Semiconductor lasers are ubiquitous in modern technology, found in everything from smartphones to fiber optic communications. However, their potential has been limited by a lack of coherence and the inability to generate visible light efficiently," explains Professor Brès . "Our work not only improves the coherence of these lasers but also shifts their output towards the visible spectrum, opening up new avenues for their use."Coherence, in this context, refers to the uniformity of the phases of the light waves emitted by the laser. High coherence means the light waves are synchronized, leading to a beam with a very precise color or frequency. This property is crucial for applications where precision and stability of the laser beam are paramount, such as time keeping and precision sensing.Increased accuracy and improved functionality The team's approach involves coupling commercially available semiconductor lasers with a silicon nitride chip. This tiny chip is created with industry-standard, cost-efficient CMOS technology. Thanks to the material’s exceptional low-loss properties, there is little to no light that is absorbed or escapes. The light from the semiconductor laser flows through microscopic waveguides into extremely small cavities, where the beam is trapped. These cavities, called micro-ring resonators, are intricately designed to resonate at specific frequencies, selectively amplifying the desired wavelengths while attenuating others, thereby achieving enhanced coherence in the emitted light.The other significant achievement is the hybrid system’s ability to double the frequency of the light coming from the commercial semiconductor laser— enabling a shift from the near-infrared spectrum to the visible light spectrum. The relationship between frequency and wavelength is inversely proportional, meaning that if the frequency is doubled, the wavelength is reduced by half. While the near infrared spectrum is exploited for telecommunications, higher frequencies are essential for building smaller, more efficient devices where shorter wavelengths are needed, such as in atomic clocks and medical devices.These shorter wavelengths are achieved when the trapped light in the cavity undergoes a process called all-optical poling, which induces what is known as second-order nonlinearity in the silicon nitride. Nonlinearity in this context means that there is a significant shift, a jump in magnitude, in the light's behavior that is not directly proportional to its frequency, arising from its interaction with the material. Silicon nitride does not normally incur this specific second order nonlinear effect, and the team performed an elegant engineering feat to induce it: The system takes advantage of the light’s capacity, when resonating within the cavity, to produce an electromagnetic wave that provokes the nonlinear properties in the material.<h2>An enabling technology for future applications</h2>"We are not just improving existing technology but also pushing the boundaries of what's possible with semiconductor lasers," says Marco Clementi, who played a key role in the project. "By bridging the gap between telecom and visible wavelengths, we're opening the door to new applications in fields like biomedical imaging and precision timekeeping."<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1703080828384-ezgif-2-416faa76dd.jpg" style="width: 300px;" class="fr-fic fr-dib">Professor Camille Brès and Marco Clementi in the lab. - 2023 EPFL/Alain Herzog - CC-BY-SA 4.0One of the most promising applications of this technology is in metrology, particularly in the development of compact atomic clocks. The history of navigational advancements hinges on the portability of accurate timepieces—from determining longitude at sea in the 16th Century to ensuring the accurate navigation of space missions and achieving better geo-localization today. "This significant advancement lays the groundwork for future technologies, some of which are yet to be conceived," notes Clementi.The team’s deep understanding of photonics and material science will potentially lead to smaller and lighter devices and lower the energy consumption and production costs of lasers. Their ability to take a fundamental scientific concept and translate it into a practical application using industry standard fabrication underscores the potential of solving complex technological challenges that can lead to unforeseen advances.<hr>ReferencesClementi, M., Nitiss, E., Durán-Valdeiglesias, E., Belahsene, S., Liu, J., Kippenberg, T. J., Debrégeas, H., &amp; Brès, C.-S. (2023). A chip-scale second-harmonic source via injection-locked all-optical poling. Light: Science &amp; Applications.&nbsp;<a href="https://doi.org/10.1038/s41377-023-01329-6" title="https://doi.org/10.1038/s41377-023-01329-6" target="_blank" rel="noopener">https://doi.org/10.1038/s41377-023-01329-6</a>

The micro-resonator being activated by a semi-conductor laser. - 2023 EPFL/Alain Herzog - CC-BY-SA 4.0

EPFL researchers have developed a hybrid device that significantly improves existing, ubiquitous laser technology.

A micro-ring resonator with big potential

New research from the lab of Caltech's&nbsp;<a href="https://www.eas.caltech.edu/people/lvw" target="_blank">Lihong Wang</a>, the Bren Professor of Medical Engineering and Electrical Engineering, is the latter. In a paper published in the journal&nbsp;Nature Biomedical Engineering, Wang and postdoctoral scholar Yide Zhang show how they have simplified and improved&nbsp;<a href="https://www.caltech.edu/about/news/advancement-simplifies-laser-based-medical-imaging" target="_blank">an imaging technique</a> they first announced in 2020.That technique, a form of photoacoustic imaging technology called PATER (Photoacoustic Topography Through an Ergodic Relay), is a specialty of Wang's group.In photoacoustic imaging, laser light is pulsed into tissue where it is absorbed by the tissue's molecules, causing them to vibrate. Each vibrating molecule serves as a source of ultrasonic waves that can be used to image the internal structures in a fashion similar to how ultrasound imaging is performed.However, photoacoustic imaging is technologically challenging because it produces all its imaging information in one short burst. To capture that information, early versions of Wang's photoacoustic imaging technology required arrays of hundreds of sensors (transducers) to be pressed against the surface of the tissue being imaged, which made the technology complicated and expensive.Wang and Zhang reduced the number of required transducers by using a device called an ergodic relay, which slows down the rate at which information (in the form of vibrations) flows into a transducer. As explained in a&nbsp;<a href="https://www.caltech.edu/about/news/advancement-simplifies-laser-based-medical-imaging" target="_blank">previous story</a> about PATER:In computing, there are two main ways to transmit data: serial and parallel. In serial transmission, the data are sent in a single stream through one communication channel. In parallel transmission, several pieces of data are sent at the same time using multiple communication channels.The two types of communication are roughly analogous to the way cash registers might be used in a store. Serial communication would be like having one cash register. Everyone gets in the same line and sees the same cashier. Parallel communication would be like having several registers and a line for each.The system Wang designed with 512 sensors is similar to the store with many cash registers. All of the sensors are working at the same time, with each taking in part of the data about the ultrasonic vibrations generated by the laser pulse.Since the ultrasonic vibrations from the system come in one short burst, a single sensor would be overwhelmed if it were used to try and collect all the data in that short amount of time. That's where the ergodic relay comes in.As Wang describes it, an ergodic relay is a sort of chamber around which sound can echo. When the ultrasonic vibrations pass through the ergodic relay, they are stretched out in time. To return to the cash-register metaphor, it would be like having another employee assisting the single cashier by telling the customers to walk a few laps around the store until the cashier is ready to see them, so the cashier does not become overwhelmed.The latest version of this technology, called PACTER (Photoacoustic Computed Tomography Through an Ergodic Relay) goes even further, allowing the system to operate using a single transducer that, through the use of software, can collect as much data as 6,400 transducers.<iframe width="640" height="360" src="https://www.youtube.com/embed/L7r5eNtaLq4?&amp;wmode=opaque&amp;rel=0&amp;enablejsapi=1&amp;origin=https://www.wevolver.com" frameborder="0" allowfullscreen="" class="fr-draggable" data-lf-vimeo-playback-inspected-kn9eq4roawkarlvp="true" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" data-lf-form-tracking-inspected-kn9eq4roawkarlvp="true"></iframe>PACTER improves on PATER in two other ways, says Wang, who is also the Andrew and Peggy Cherng Medical Engineering Leadership Chair and executive officer for medical engineering.One improvement is that PACTER can create three-dimensional images, whereas PATER can only generate 2D images. This was enabled by the development of improved software."Transitioning to 3D imaging significantly escalates the data requirement. The challenge was funneling the immensely increased data through a single transducer," Zhang says. "Our solution emerged by altering our approach. Rather than a direct and computationally intensive method of reconstructing 3-D images from the single-transducer data, we first expanded one transducer into thousands of virtual ones. This idea simplified the process of 3D image reconstruction, aligning it more closely with the traditional methods in our photoacoustic imaging."Secondly, unlike PATER, PACTER does not need to be calibrated each time it is used."With PATER, we had to calibrate it each time to use it and that's just not practical. We got rid of this per-use single-time calibration," Wang says.Calibration was needed because when the system fires a pulse of laser light into tissue, an "echo" of that pulse would bounce back into the transducer, preventing it from sensing direct ultrasound information.Wang says PACTER gets around that issue by adding something called a delay line to the system. The delay line forces the echo to take a longer physical path on its way back to the transducer so that it arrives after the direct ultrasound information has been received."Even though I always said this was possible, I knew it would be challenging," Wang says.The paper describing the work, "Ultrafast longitudinal imaging of haemodynamics via single-shot volumetric photoacoustic tomography with a single-element detector," appears in the November 30 issue of&nbsp;Nature Biomedical Engineering. Co-authors are Peng Hu (PhD '23), former graduate student in medical engineering; Lei Li (PhD '19), former postdoc in medical engineering; Rui Cao, postdoc in medical engineering; Anjul Khadria, former postdoc in medical engineering; Konstantin Maslov, former staff scientist at Caltech; Xin Tong, graduate student in medical engineering; and Yushun Zeng, Laiming Jiang, and Qifa Zhou of USC.

There are times when scientific progress comes in the form of discovering something completely new. Other times, progress boils down to doing something better, faster, or more easily.

Advancements Make Laser-Based Imaging Simpler and Three-Dimensional

The practice of keeping time hinges on stable oscillations. In a grandfather clock, the length of a second is marked by a single swing of the pendulum. In a digital watch, the vibrations of a quartz crystal mark much smaller fractions of time. And in atomic clocks, the world’s state-of-the-art timekeepers, the oscillations of a laser beam stimulate atoms to vibrate at 9.2 billion times per second. These smallest, most stable divisions of time set the timing for today’s satellite communications, GPS systems, and financial markets.A clock’s stability depends on the noise in its environment. A slight wind can throw a pendulum’s swing out of sync. And heat can disrupt the oscillations of atoms in an atomic clock. Eliminating such environmental effects can improve a clock’s precision. But only by so much.A new MIT study finds that even if all noise from the outside world is eliminated, the stability of clocks, laser beams, and other oscillators would still be vulnerable to quantum mechanical effects. The precision of oscillators would ultimately be limited by quantum noise.But in theory, there’s a way to push past this quantum limit. In their study, the researchers also show that by manipulating, or “squeezing,” the states that contribute to quantum noise, the stability of an oscillator could be improved, even past its quantum limit.“What we’ve shown is, there’s actually a limit to how stable oscillators like lasers and clocks can be, that’s set not just by their environment, but by the fact that quantum mechanics forces them to shake around a little bit,” says Vivishek Sudhir, assistant professor of mechanical engineering at MIT. “Then, we’ve shown that there are ways you can even get around this quantum mechanical shaking. But you have to be more clever than just isolating the thing from its environment. You have to play with the quantum states themselves.”The team is working on an experimental test of their theory. If they can demonstrate that they can manipulate the quantum states in an oscillating system, the researchers envision that clocks, lasers, and other oscillators could be tuned to super-quantum precision. These systems could then be used to track infinitesimally small differences in time, such as the fluctuations of a single qubit in a quantum computer or the presence of a dark matter particle flitting between detectors.“We plan to demonstrate several instances of lasers with quantum-enhanced timekeeping ability over the next several years,” says Hudson Loughlin, a graduate student in MIT’s Department of Physics. “We hope that our recent theoretical developments and upcoming experiments will advance our fundamental ability to keep time accurately, and enable new revolutionary technologies.”Loughlin and Sudhir detail their work in an open-access&nbsp;<a href="https://www.nature.com/articles/s41467-023-42739-9" target="_blank">paper published in the journal&nbsp;Nature Communications</a>.<h2>Laser precision</h2>In studying the stability of oscillators, the researchers looked first to the laser — an optical oscillator that produces a wave-like beam of highly synchronized photons. The invention of the laser is largely credited to physicists Arthur Schawlow and Charles Townes, who coined the name from its descriptive acronym: light amplification by stimulated emission of radiation.A laser’s design centers on a “lasing medium” — a collection of atoms, usually embedded in glass or crystals. In the earliest lasers, a flash tube surrounding the lasing medium would stimulate electrons in the atoms to jump up in energy. When the electrons relax back to lower energy, they give off some radiation in the form of a photon. Two mirrors, on either end of the lasing medium, reflect the emitted photon back into the atoms to stimulate more electrons, and produce more photons. One mirror, together with the lasing medium, acts as an “amplifier” to boost the production of photons, while the second mirror is partially transmissive and acts as a “coupler” to extract some photons out as a concentrated beam of laser light.Since the invention of the laser, Schawlow and Townes put forth a hypothesis that a laser’s stability should be limited by quantum noise. Others have since tested their hypothesis by modeling the microscopic features of a laser. Through very specific calculations, they showed that indeed, imperceptible, quantum interactions among the laser’s photons and atoms could limit the stability of their oscillations.“But this work had to do with extremely detailed, delicate calculations, such that the limit was understood, but only for a specific kind of laser,” Sudhir notes. “We wanted to enormously simplify this, to understand lasers and a wide range of oscillators."<h2>Putting the “squeeze” on</h2>Rather than focus on a laser’s physical intricacies, the team looked to simplify the problem.“When an electrical engineer thinks of making an oscillator, they take an amplifier, and they feed the output of the amplifier into its own input,” Sudhir explains. “It’s like a snake eating its own tail. It’s an extremely liberating way of thinking. You don’t need to know the nitty gritty of a laser. Instead, you have an abstract picture, not just of a laser, but of all oscillators.”In their study, the team drew up a simplified representation of a laser-like oscillator. Their model consists of an amplifier (such as a laser’s atoms), a delay line (for instance, the time it takes light to travel between a laser’s mirrors), and a coupler (such as a partially reflective mirror).The team then wrote down the equations of physics that describe the system’s behavior, and carried out calculations to see where in the system quantum noise would arise.“By abstracting this problem to a simple oscillator, we can pinpoint where quantum fluctuations come into the system, and they come in in two places: the amplifier and the coupler that allows us to get a signal out of the oscillator,” Loughlin says. “If we know those two things, we know what the quantum limit on that oscillator’s stability is.”Sudhir says scientists can use the equations they lay out in their study to calculate the quantum limit in their own oscillators.What’s more, the team showed that this quantum limit might be overcome, if quantum noise in one of the two sources could be “squeezed.” Quantum squeezing is the idea of minimizing quantum fluctuations in one aspect of a system at the expense of proportionally increasing fluctuations in another aspect. The effect is similar to squeezing air from one part of a balloon into another.In the case of a laser, the team found that if quantum fluctuations in the coupler were squeezed, it could improve the precision, or the timing of oscillations, in the outgoing laser beam, even as noise in the laser’s power would increase as a result.“When you find some quantum mechanical limit, there’s always some question of how malleable is that limit?” Sudhir says. “Is it really a hard stop, or is there still some juice you can extract by manipulating some quantum mechanics? In this case, we find that there is, which is a result that is applicable to a huge class of oscillators.”

Clocks, lasers, and other oscillators could be tuned to super-quantum precision, allowing researchers to track infinitesimally small differences in time, according to a new MIT study. Image: MIT News; iStock

More stable clocks could measure quantum phenomena, including the presence of dark matter.

With a quantum "squeeze," clocks could keep even more precise time, MIT researchers propose

In those latter applications, lasers that can emit extremely short pulses—those on the order of one-trillionth of a second (one picosecond) or shorter—are especially useful. Using lasers operating on such small timescales, researchers can study physical and chemical phenomena that occur extremely quickly—for example, the making or breaking of molecular bonds in a chemical reaction or the movement of electrons within materials. These ultrashort pulses are also extensively used for imaging applications because they can have extremely large peak intensities but low average power, so they avoid heating or even burning up samples such as biological tissues.In a paper appearing in the journal Science, Caltech's <a href="https://www.eas.caltech.edu/people/amarandi" target="_blank">Alireza Marandi</a>, an assistant professor of electrical engineering and applied physics, describes a new method developed by his lab for making this kind of laser, known as a mode-locked laser, on a photonic chip. The lasers are made using nanoscale components (a nanometer is one-billionth of a meter), allowing them to be integrated into light-based circuits similar to the electricity-based integrated circuits found in modern electronics."We're not just interested in making mode-locked lasers more compact," Marandi says. "We are excited about making a well-performing mode-locked laser on a nanophotonic chip and combining it with other components. That's when we can build a complete ultrafast photonic system in an integrated circuit. This will bring the wealth of ultrafast science and technology, currently belonging to meter-scale experiments, to millimeter-scale chips."Ultrafast lasers of this sort are so important to research, that this year's Nobel Prize in Physics was awarded to a trio of scientists for the development of lasers that produce attosecond pulses (one attosecond is one-quintillionth of a second). Such lasers, however, are currently extremely expensive and bulky, says Marandi—who notes that his research is exploring methods to achieve such timescales on chips that can be orders of magnitude cheaper and smaller, with the aim of developing affordable and deployable ultrafast photonic technologies."These attosecond experiments are done almost exclusively with ultrafast mode-locked lasers," he says. "And some of them can cost as much as $10 million, with a good chunk of that cost being the mode-locked laser. We are really excited to think about how we can replicate those experiments and functionalities in nanophotonics."At the heart of the nanophotonic mode-locked laser developed by Marandi's lab is lithium niobate, a synthetic salt with unique optical and electrical properties that, in this case, allows the laser pulses to be controlled and shaped through the application of an external radio-frequency electrical signal. This approach is known as active mode-locking with intracavity phase modulation."About 50 years ago, researchers used intracavity phase modulation in tabletop experiments to make mode-locked lasers and decided that it was not a great fit compared to other techniques," says Qiushi Guo, the first author of the paper and a former postdoctoral scholar in Marandi's lab. "But we found it to be a great fit for our integrated platform.""Beyond its compact size, our laser also exhibits a range of intriguing properties. For example, we can precisely tune the repetition frequency of the output pulses in a wide range. We can leverage this to develop chip-scale stabilized frequency comb sources, which are vital for frequency metrology and precision sensing," adds Guo, who is now an assistant professor at the City University of New York Advanced Science Research Center.Marandi says he aims to continue improving this technology so it can operate at even shorter timescales and higher peak powers, with a goal of 50 femtoseconds (a femtosecond is one-quadrillionth of a second), which would be a 100-fold improvement over his current device, which generates pulses 4.8 picoseconds in length.<hr>The paper describing the research is titled "<a href="https://www.science.org/doi/10.1126/science.adj5438" target="_blank">Ultrafast mode-locked laser in nanophotonic lithium niobite</a>" and appears in the November 9 issue of Science. Co-authors are Benjamin K. Gutierrez (MS '23), graduate student in applied physics; electrical engineering graduate students Ryoto Sekine (MS '22), Robert M. Gray (MS '22), James A. Williams, Selina Zhou (BS '22), and Mingchen Liu; Luis Ledezma (PhD '23), an external affiliate in electrical engineering; Luis Costa, formerly at Caltech and now with JPL, which Caltech manages for NASA; and Arkadev Roy (MS '23, PhD '23), formerly of Caltech and now with UC Berkeley .

Lasers have become relatively commonplace in everyday life, but they have many uses outside of providing light shows at raves and scanning barcodes on groceries. Lasers are also of great importance in telecommunications and computing as well as biology, chemistry, and physics research.

Ultrafast Lasers on Ultra-Tiny Chips

Small satellites are becoming increasingly compact and powerful. The technology of conventional radio channels is reaching its limits due to the rising number of satellites. Laser communications offers solutions for the efficient transmission of high data volumes without interfering with other channels. For this application, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) <a href="https://www.dlr.de/en/kn" target="_blank">Institute of Communications and Navigation</a>, together with the company Tesat-Spacecom GmbH &amp; Co. KG <a href="https://www.tesat.de/" target="_blank" rel="noopener noreferrer">TESAT</a>, developed OSIRIS4CubeSat, the world's smallest commercially available laser communications terminal. The reliability and error-free functionality of the terminal, which was specifically developed for use on microsatellites, was confirmed during a test mission in space.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1699086525920-image-1600-66c2779f82a779fcbe74aba8d1b6a0ad.jpeg" style="width: 766px;" class="fr-fic fr-dib">The highly compact communication terminal CubeLCT was developed at the DLR Institute of Communication and Navigation on behalf of the company Tesat Spacecom. It is prepared for series production and can be integrated and adjusted with a few degrees of freedom. Credit: DLR (CC BY-NC-ND 3.0)"This success is the result of our many years of research in the field of optical satellite communications," says Florian David, Director of the DLR Institute of Communications and Navigation. "It demonstrates the impressive potential for designing small, light and at the same time powerful optical satellite terminals. This is an important building block for future satellite systems, for example for Earth observation or in megaconstellations."<h2>Microsatellite with an optical communications system</h2>The first OSIRIS4CubeSat terminal was launched into space on board the CubeL satellite on 24 January 2021. During the <a href="https://www.dlr.de/de/aktuelles/nachrichten/2021/01/20210124_pionierstart-kleinsatellit-mit-kleinstem-laserterminal-der-welt" target="_blank">PIXL-1 mission</a>, images acquired by the camera system on CubeL could be sent to the Optical Ground Station Oberpfaffenhofen using the OSIRIS4CubeSat laser. Both the satellite and the laser terminal have since undergone extensive testing. Now the tests have been successfully completed with an end-to-end demonstration. The reliability and error-free functionality of OSIRIS4CubeSat in space have been confirmed.Microsatellites, or CubeSats, have a standardised cube shape with an edge length of 10 centimetres and can be extended as required. The laser communications terminal developed in the <a href="https://www.dlr.de/kn/en/desktopdefault.aspx/tabid-17840/#gallery/36173" target="_blank" rel="noopener noreferrer">OSIRIS4CubeSat</a> project together with TESAT complies with this standard. The patented design, in which an electronic circuit board was used as the mechanical basis for the optical elements for the first time, made it possible to achieve a high degree of compactness.<h2>High data transmission rates without electromagnetic interference</h2>With a data rate of 100 megabits per second, the laser terminal's speed far surpasses the transmission capabilities of comparable radio systems. In addition to the high data rate, laser light as a transmission medium is unaffected by electromagnetic interference. Channel crosstalk, as often occurs with conventional radio channels, does not exist with laser transmission. This means that laser transmission channels do not require lengthy approval procedures on the part of the Federal Network Agency (Bundesnetzagentur; BNetzA) or the International Telecommunication Union (ITU).When transmitting image data to Earth by laser, encoding procedures developed at DLR were employed to safeguard the data. This is necessary to maintain stable, zero-loss transmission from the satellite to Earth, since the data must be protected from disruptions caused by atmospheric effects. For this purpose, they are encoded on the satellite before being sent to the ground station using the laser link. There, following reception, they are decoded and then processed. The <a href="https://www.dlr.de/en/research-and-transfer/projects-and-missions/iss/the-german-space-operations-center" target="_blank">German Space Operations Center (GSOC)</a> is responsible for the commanding, operation and support of the satellite. CubeL is thus the first CubeSat to be successfully integrated into GSOC's existing ground segment.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1699086552505-image-1600-a23a7a8f570e1abd2658cf00a0296875.jpeg" style="width: 766px;" class="fr-fic fr-dib">The new op­ti­cal ground sta­tion on the roof of the DLR In­sti­tute of Com­mu­ni­ca­tions and Nav­i­ga­tion in Oberp­faf­fen­hofen. Credit: DLR (CC BY-NC-ND 3.0)<h2>From research to industrial application</h2>The results from PIXL-1 show the error-free functionality of the OSIRIS4CubeSat terminal along the complete transmission chain. This will enable widespread use of laser communications on a large number of satellites in the future. The technology was transferred to TESAT even before the demonstration mission was completed. TESAT has since incorporated the terminal into its portfolio and offers it to commercial customers under the name 'CubeLCT' or 'SCOT20', which is a further development of the product.Siegbert Martin, Chief Technology Officer at TESAT said: "This underlines the great opportunities that arise from cooperation between research and industry in Germany."

The PIXL-1 small satellite can acquire images of the Earth with a high-resolution camera and send them to the Optical Ground Station Oberpfaffenhofen with the CubeLCT via a laser link. Credit: DLR (CC BY-NC-ND 3.0)

Small satellites are becoming increasingly compact and powerful. The technology of conventional radio channels is reaching its limits due to the rising number of satellites.

Demonstration of data transmission from a microsatellite by laser

This article originally appeared in <a href="https://news.itmo.ru/en/science/life_science/news/13440/" target="_blank" rel="noopener noreferrer">ITMO News</a> and has been republished with permission.<hr>A family of medical devices named implants are manufactured to replace a missing organ or its parts. Dental implants are implanted into the jaw to support replacement teeth. Apart from dentistry, implants are also used to resurface a knee, repair skull bones, as well as for other purposes.&nbsp;All medical devices are customized to each patient's unique characteristics. In the case of dental implants, doctors must be aware of a person's skull bones, gums, and roots to determine the appropriate form and size of the future implant.&nbsp;To make an implant last longer, as well as heal faster and easier, its surface is enhanced with functional features, like antibacterial properties and biocompatibility. The latter is usually accomplished by roughening up the implant's surface with sandblasting, followed by acid and anodizing to make the surface antimicrobial. So far, there is no one-stop complex to execute both procedures – except for the one currently under development at ITMO University.<img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjk3MTk5NTcwODA3LXAxMzQ0MC5qcGciLCJlZGl0cyI6eyJyZXNpemUiOnsid2lkdGgiOjk1MCwiZml0IjoiY292ZXIifX19" style="width: 766px;" class="fr-fic fr-dib">The research team (from left to right): Yulia Karlagina, Galina Romanova, Andrey Lisichnikov, and Fedor Inochkin. Photo courtesy of Evgeniy Shamshin<h2 dir="ltr" id="isPasted">The laser-based complex</h2>Researchers from ITMO’s Institute of Laser Technologies and their colleagues from Laser Center designed a multiuse robotic complex for surface treatment of diverse medical materials. According to the developers, the technology is equipped with a fiber laser system and possesses several advantages:&nbsp;Versatility. The technology is well-suited for use with medical devices such as scalpels and surgical scissors, as well as a variety of implants, including teeth, skull, hip, and knee replacements.&nbsp;Turnkey treatment in one system. The team created and merged several laser treatment options that are used consecutively:<ul><li dir="ltr">The technology for antibacterial surface properties prevents bacterial complications, which lead to implant rejection. Laser heating makes oxide layers grow on the surface of a titanium implant, which demonstrates bactericidal properties when exposed to a UV source.</li><li dir="ltr">The technology for biocompatible surface property. The laser is applied to generate a relief with unique properties on the surface, followed by the laser ablation process, which creates a biomimetic micro- and nanorelief that promotes excellent adhesion of proteins in the early stages of osseointegration, cell proliferation, and differentiation, ensuring implant success.&nbsp;</li><li dir="ltr">The technology for applying non-toxic identification labels on medical devices. Legally binding product labeling makes it possible to track the life cycle of a product, from its early production to the end user.&nbsp;</li></ul><blockquote>“We came up with a versatile device that makes it possible to functionalize a wide spectrum of medical equipment without any additional consumables or tools. The single system can boast several treatment options, related to the biocompatible and antibacterial properties of products, their roughness, as well as labeling,” states&nbsp;Yulia Karlagina, a junior researcher at ITMO’s Institute of Laser Technologies.</blockquote><img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1697199551134-ezgif-2-348e4b0195.gif" style="width: 766px;" class="fr-fic fr-dib">The robot laser complex in action. Video courtesy of Evgeniy ShamshinCompatibility with custom devices. All it takes is to load a 3D model of the implant into the program and indicate which elements of the 3D electronic geometric model need to be processed. The software was developed by the team at ITMO.&nbsp;The complex consists of a six-axis robotic manipulator and a laser scanning system mounted on the robot's arm, which ensures high accuracy of laser positioning, achieved by optical methods, and universality of robotic systems. Its ability to focus a laser beam on a product’s surface in all six spatial coordinates makes it possible to process products of complex shapes in one technological cycle.The team incorporated a computer vision system to make it easier for the operator to determine the position of the product in reality. In addition to its position, the system reports on its orientation and geometrical parameters to ensure precision laser processing.<blockquote>“The existing robotic solutions are aimed at mass-production items. Once adjusted for a specific device, they perform a series of programmed actions again and again. This approach is not suitable for small-scale or one-of-a-kind equipment, whereas our technology can be easily customized for a new product,” explains&nbsp;Fedor Inochkin, a researcher at ITMO’s Institute of Laser Technologies<img data-fr-image-pasted="true" alt="" src="https://news.itmo.ru/en/science/life_science/news/13440/" class="fr-fic fr-dii"></blockquote><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjk3MTk5Mzg4MjEyLTEzNDQwMDEuanBnIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 766px;" class="fr-fic fr-dib">An operator positions a medical device and loads a 3D model into the system, selects the areas to be processed, and starts the program. The robot manipulator travels from one area to another with a laser beam. The procedure time varies depending on the chosen technology and item size. Photo courtesy of Evgeniy ShamshinA compact automated laser system for dental implants and their components is another device created by the team to serve exclusively dental purposes.&nbsp;<blockquote>“The systems have different functions, which affects their price and audience. If a customer needs to process a certain implant, like a dental one, they should purchase the second device, whereas the first one will be more beneficial with a wide range of items, including custom ones. For instance, a person who suffered from head injury can receive an individually designed skull implant. The multiuse system allows specialists to incorporate a desired set of properties into personalized implants in accordance to their unique shape,” notes Yulia Karlagina.&nbsp;</blockquote><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjk3MTk5NDEwOTc4LTEzNDQwMDIuanBnIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 766px;" class="fr-fic fr-dib">An operator positions an implant, closes the complex’s cover, chooses the type of device under study and processing mode in the program, and, finally, starts the program. The implant is ready in 10-15 minutes. Photo courtesy of Evgeniy Shamshin<h2 dir="ltr" id="isPasted">Prospects of the technology</h2>The ITMO researchers in collaboration with their co-authors from Samara State University have carried out preliminary testing of both complexes, in particular preclinical trials of the processed medical devices. All samples were successfully tested in vitro and in vivo and are recommended for clinical trials.&nbsp;In the future, the developers plan to run acceptance tests to ensure the complexes are ready for operation and mass production. The team also intends to attract new industrial partners. In the long run, the systems are expected to be used in the production of medical equipment and implants.&nbsp;<blockquote>“We already have surface functionalization technologies for implants and soon we, with our colleagues from Laser Center, will start to look for new partners who will integrate them into their productions. If requested, we can also modify our products to the client’s needs – for instance, we can add a second robot manipulator that will upload new implants into the system instead of an operator,” notes Galina Romanova, a senior researcher at ITMO’s Institute of Laser Technologies.&nbsp;</blockquote><img src="https://images.wevolver.com/eyJidWNrZXQiOiJ3ZXZvbHZlci1wcm9qZWN0LWltYWdlcyIsImtleSI6ImZyb2FsYS8xNjk3MTk5NDQxMTQzLTEzNDQwMDMuanBnIiwiZWRpdHMiOnsicmVzaXplIjp7IndpZHRoIjo5NTAsImZpdCI6ImNvdmVyIn19fQ==" style="width: 766px;" class="fr-fic fr-dib">Galina Romanova. Photo courtesy of Evgeniy ShamshinThe project is implemented as part of the Government Decree No. 218 on request by Laser Center. Additionally, the developers continue to run research within ITMO’s 2030 Development Strategy.&nbsp;The research team has been working on the processing of medical titanium alloys for several years now. Together with their partners from Lenmiriot, they <a href="https://news.itmo.ru/en/science/new_materials/news/9655/" target="_blank">developed</a> a design of an implant surface that helps implants heal faster without inflammation. In 2022, Lenmiriot <a href="https://news.itmo.ru/en/startups_and_business/partnership/news/12313/" target="_blank">announced</a> the market launch of the dental implants made with the new laser technology.

The robot laser complex. Photo courtesy of Evgeniy Shamshin

Researchers from ITMO University have created a multipurpose robot complex for laser treatment of medical device surfaces, like those of dental and skull implants. The designed technology can be utilized to imbue metal implants with antibacterial and biocompatible properties, as well as mark medical items. All one needs to do is load a 3D model of an implant into a program, set a processing trajectory, and pick a surface attribute of choice.

A Multiuse Robot for Medical Applications Designed at ITMO

This article originally appeared in <a href="https://engineering.princeton.edu/news/2023/10/11/illuminating-errors-creates-new-paradigm-quantum-computing" target="_blank" rel="noopener noreferrer">Princeton University</a> and has been republished with permission.<hr>Researchers have developed a method that can reveal the location of errors in quantum computers, making them up to ten times easier to correct. This will significantly accelerate progress towards large-scale quantum computers capable of tackling the world’s most challenging computational problems, the researchers said.Led by Princeton University’s <a href="https://ece.princeton.edu/people/jeff-thompson" target="_blank">Jeff Thompson</a>, the team demonstrated a way to identify when errors occur in quantum computers more easily than ever before. This is a new direction for research into quantum computing hardware, which more often seeks to simply lower the probability of an error occurring in the first place.A <a href="https://www.nature.com/articles/s41586-023-06438-1" target="_blank">paper</a> detailing the new approach was published in Nature on Oct. 11. Thompson’s collaborators include Shruti Puri at Yale University and Guido Pupillo at the University of Strasbourg.Physicists have been inventing new qubits – the core component of quantum computers – for nearly three decades, and steadily improving those qubits to be less fragile and less prone to error. But some errors are inevitable no matter how good qubits get. The central obstacle to the future development of quantum computers is being able to correct for these errors. However, to correct an error, you first have to figure out if an error occurred, and where it is in the data. And typically, the process of checking for errors introduces more errors, which have to be found again, and so on.Quantum computers’ ability to manage those inevitable errors has remained more or less stagnant over that long period, according to Thompson, associate professor of electrical and computer engineering. He realized there was an opportunity in biasing certain kinds of errors.“Not all errors are created equal,” he said.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1697112488641-Thompson-erasure-for-web-02.jpg" style="width: 766px;" class="fr-fic fr-dib">At the heart of this quantum computer, lasers control the states of individual atoms, manipulating information based on the extremely subtle physics of those atoms’ energy levels. Photo by Frank WojciechowskiThompson’s lab works on a type of quantum computer based on neutral atoms. Inside the ultra-high vacuum chamber that defines the computer, qubits are stored in the spin of individual ytterbium atoms held in place by focused laser beams called optical tweezers. In this work, a team led by graduate student Shuo Ma used an array of 10 qubits to characterize the probability of errors occurring while first manipulating each qubit in isolation, then manipulating pairs of qubits together.They found error rates near the state of the art for a system of this kind: 0.1 percent per operation for single qubits and 2 percent per operation for pairs of qubits.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1697112509360-Qbit-erasure-final-Illustration-2048x1152.jpg" style="width: 766px;" class="fr-fic fr-dib">A team led by Jeff Thompson, associate professor of electrical and computer engineering, pioneered an approach to more efficient error correction in quantum computers. (Illustration by Gabriele Meilikhov/Muza Productions)However, the main result of the study is not only the low error rates, but also a different way to characterize them without destroying the qubits. By using a different set of energy levels within the atom to store the qubit, compared to previous work, the researchers were able to monitor the qubits during the computation to detect the occurrence of errors in real time. This measurement causes the qubits with errors to emit a flash of light, while the qubits without errors remain dark and are unaffected.This process converts the errors into a type of error known as an erasure error. Erasure errors have been studied in the context of qubits made from photons, and have long been known to be simpler to correct than errors in unknown locations, Thompson said. However, this work is the first time the erasure-error model has been applied to matter-based qubits. It follows a <a href="https://www.nature.com/articles/s41467-022-32094-6" target="_blank">theoretical proposal</a> last year from Thompson, Puri and Shimon Kolkowitz of the University of California-Berkeley.In the demonstration, approximately 56 percent of one-qubit errors and 33 percent of two-qubit errors were detectable before the end of the experiment. Crucially, the act of checking for errors doesn’t cause significantly more errors: The researchers showed that checking increased the rate of errors by less than 0.001 percent. According to Thompson, the fraction of errors detected can be improved with additional engineering.The researchers believe that, with the new approach, close to 98 percent of all errors should be detectable with optimized protocols. This could reduce the computational costs of implementing error correction by an order of magnitude or more.Other groups have already started to adapt this new error detection architecture. Researchers at Amazon Web Services and a separate group at Yale have independently shown how this new paradigm can also improve systems using superconducting qubits.“We need advances in many different areas to enable useful, large-scale quantum computing. One of the challenges of systems engineering is that these advances that you come up with don’t always add up constructively. They can pull you in different directions,” Thompson said. “What’s nice about erasure conversion is that it can be used in many different qubits and computer architectures, so it can be deployed flexibly in combination with other developments.”Additional authors on the paper “High-fidelity gates with mid-circuit erasure conversion in a metastable neutral atom qubit” include Shuo Ma, Genyue Liu, Pai Peng, Bichen Zhang, and Alex P. Burgers, at Princeton; Sven Jandura at Strasbourg; and Jahan Claes at Yale. This work was supported in part by the Army Research Office, the Office of Naval Research, DARPA, the National Science Foundation and the Sloan Foundation.

Researchers led by Jeff Thompson at Princeton University have developed a technique to make it 10 times easier to correct errors in a quantum computer. Photos by Frank Wojciechowski

Researchers have developed a method that can reveal the location of errors in quantum computers, making them up to ten times easier to correct. This will significantly accelerate progress towards large-scale quantum computers capable of tackling the world’s most challenging computational problems, the researchers said.

Illuminating errors creates a new paradigm for quantum computing

A new perforated metalens proves it is possible to use nano-optics to focus beams of extreme ultraviolet light (EUV) and could open new doors in microscopy, sensing, holography, and fundamental physics research. The advance is reported in&nbsp;Science.At the&nbsp;<a href="https://seas.harvard.edu/" target="_blank">Harvard John A. Paulson School of Engineering and Applied Sciences</a> (SEAS),&nbsp;<a href="https://seas.harvard.edu/person/federico-capasso" target="_blank">Federico Capasso&rsquo;s</a> lab unveiled in 2011 the groundbreaking concept of refracting metasurfaces, or sub-wavelength-spaced arrays of nanostructures, with a&nbsp;Science&nbsp;paper that has since been cited 7,000 times. In 2016, another&nbsp;Science&nbsp;paper reported the use of high-performance flat lenses made up of nanopillars and fabricated using lithography techniques, which unlocked a new strategy to focus light. That work was a major leap forward for conventional optical devices that had historically been fabricated by molding, making them thick and bulky.Since that initial metalens demonstration, researchers far and wide have been adopting the technique to create metalens designs that exert increasingly complex control over visible and infrared light &ndash; but harnessing such metasurfaces to control light in the EUV range has remained out of reach. EUV wavelengths are extremely small, around the 50-nanometer range, which is much smaller than visible wavelengths of light, which are 400 to 700 nanometers in size. At such a small wavelength, EUV is absorbed by all materials, preventing that light from being refracted and controlled by transmissive optics.The Capasso group&rsquo;s latest breakthrough &ndash; fabricating a metalens that uses nano-sized holes to vacuum-guide EUV -- introduces a game-changing workaround. &ldquo;This work will revolutionize optics in a spectral region (extreme UV) where, until now, there were no lenses or viable optics for high-performance or high-volume applications,&rdquo; says Capasso, co-corresponding author, who is the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS.&nbsp;The new work was in collaboration with Martin Schultze&rsquo;s lab at Graz University of Technology.The idea was originally conceived by Marcus Ossiander, a postdoctoral fellow in Capasso&rsquo;s group, whose background is in attosecond physics, or the study of how light and matter interact on the inconceivably-small timescale of quintillionths of a second. &ldquo;The only way you can create laser pulses on the attosecond scale is using these very short wavelengths of ultraviolet light,&rdquo; Ossiander says. &ldquo;I had this big dream, a bit of a moonshot, really, to create a metalens that could control EUV. And Federico will never stop you from pursuing a dream.&rdquo;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1681143867298-cover_xuv_metalens_v2.png" style="width: 300px;" class="fr-fic fr-dib">Typical metalenses rely on the fabrication of nanopillars that &ndash; sticking up like the skyscrapers of the Manhattan skyline &ndash; refract visible light and focus it in desired ways. But with EUV light being absorbed by all materials it reaches, Ossiander knew that strategy would not work. As he contemplated the way materials interact with light that oscillates incredibly fast, a creative new idea struck him.&ldquo;Why not flip the design&hellip; to make transmissive pillars&hellip; out of air?&rdquo; he says. By making holes in the surface of a material with a lower refractive index than air itself, he hypothesized that EUV could be guided and focused using the vacuum inside the holes. When computer simulations suggested it might actually work, he teamed up with nanofabrication expert Maryna Leonidivna Meretska, a postdoctoral researcher in Capasso&rsquo;s lab, to develop a prototype.&ldquo;Fabrication, in general, requires a lot of perseverance,&rdquo; Meretska says. &ldquo;It took many attempts to realize the working sample. We learned something new about the process with every attempt, and that kept me going.&rdquo;&ldquo;This work really pushed the limits of what&rsquo;s possible in nanotechnology today,&rdquo; Capasso says. &ldquo;We needed impeccable fabrication methods to make this metalens with features small enough to interact with EUV wavelengths, which means the features must be smaller than those wavelengths. It pushed us to shrink the metalens features by a factor of 10 compared to what&rsquo;s been done before &ndash; it was really a very large leap.&rdquo;Once the prototype was complete, Ossiander flew to the Institute of Experimental Physics at Graz University of Technology in Austria, one of few labs in the world that can create EUV. There, researchers led by attosecond physicist Martin Schultze (a co-corresponding author on the study) sent EUV radiation through the metalens prototype. After many experiments, the team saw what they had long dreamed of: a small spot, indicating the concentration of light, detected by a special camera.&ldquo;Every element [of this project] worked like in an orchestra,&rdquo; Meretska says. &ldquo;Both sample fabrication and measurement processes are incredibly challenging and knowing everything worked as designed was very satisfying.&rdquo;The breakthrough will have implications for attosecond physics, as the metalens can be used to better understand light and matter interactions on the nanoparticle scale. Capasso says the semiconducting industry will also benefit from EUV metalens technology because it will enable the fabrication of smaller and smaller transistors and processors. But, perhaps most exciting, Capasso says there are likely many future applications that haven&rsquo;t yet been thought of.&ldquo;We don&rsquo;t currently know all the fields that might benefit from EUV metalenses, because no one expected that this type of technology would be possible anytime soon,&rdquo; Ossiander says.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1681143890910-lens_rect_scale.png" style="width: 766px;" class="fr-fic fr-dib">Additional authors include Hana Kristin Hampel, Soon Wei Daniel Lim, Nico Knefz, Thomas Jauk.<a href="https://otd.harvard.edu/" target="_blank">Harvard&rsquo;s Office of Technology Development</a> has protected the intellectual property arising from this study and is exploring commercialization opportunities.Part of this work was performed at Harvard&rsquo;s Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the NSF under award no. ECCS-2025158. Computations were run on the FASRC Cannon cluster supported by the FAS Division of Science Research Computing Group at Harvard University. This research was supported by the Alexander von Humboldt Foundation (Feodor-Lynen Fellowship), the Austrian Science Fund (FWF, Start Grant Y1525), the European Union (grant agreement 01076933 EUVORAM), A*STAR Singapore through the National Science Scholarship Scheme, and the Air Force Office of Scientific Research (AFOSR) under award Number FA9550-21-1- 0312.

Nanofabrication technique, using holes to create vacuum guides, breaks a barrier in optics

First-of-its-kind metalens can focus extreme ultraviolet light

As technologies keep advancing at exponential rates and demand for new devices rises accordingly, miniaturizing systems into chips has become increasingly important. Microelectronics has changed the way we manipulate electricity, enabling sophisticated electronic products that are now an essential part of our daily lives. Similarly, integrated photonics has been revolutionizing the way we control light for applications such as data communications, imaging, sensing, and biomedical devices. By routing and shaping light using micro- and nanoscale components, integrated photonics shrinks full optical systems into the size of tiny chips.&nbsp;Despite its success, integrated photonics has been missing a key component to achieve complete miniaturization: high-performance chip-scale lasers. While some progress has been made on near-infrared lasers, the visible-light lasers that currently feed photonic chips are still benchtop and expensive. Since visible light is essential for a wide range of applications including quantum optics, displays, and bioimaging, there is a need for tunable and narrow-linewidth chip-scale lasers emitting light of different colors.&nbsp;<h2>Inventing high-performance lasers that fit on a fingertip</h2>Researchers at<a href="http://engineering.columbia.edu/" target="_blank">&nbsp;Columbia Engineering</a>&rsquo;s <a href="https://lipson.ee.columbia.edu/" target="_blank">Lipson Nanophotonics Group</a> have created visible lasers of very pure colors from near-ultraviolet to near-infrared that fit on a fingertip. The colors of the lasers can be precisely tuned and extremely fast &ndash; up to 267 petahertz per second, which is critical for applications such as quantum optics. The team is the first to demonstrate chip-scale narrow-linewidth and tunable lasers for colors of light below red -- green, cyan, blue, and violet. These inexpensive lasers also have the smallest footprint and shortest wavelength (404 nm) of any tunable and narrow-linewidth integrated laser emitting visible light. The <a href="https://www.nature.com/articles/s41566-022-01120-w" target="_blank">study</a>, which was first presented at the CLEO 2021 post-deadline session on May 14, 2021, was published online December 23, 2022, by&nbsp;Nature Photonics.&ldquo;What&rsquo;s exciting about this work is that we&rsquo;ve used the power of integrated photonics to break the existing paradigm that high-performance visible lasers need to be benchtop and cost tens of thousands of dollars,&rdquo; says the study&rsquo;s lead author Mateus Corato Zanarella, a PhD student who works with <a href="https://www.engineering.columbia.edu/faculty/michal-lipson" target="_blank">Michal Lipson</a>, Higgins Professor of <a href="https://www.ee.columbia.edu/" target="_blank">Electrical Engineering</a> and professor of <a href="https://www.apam.columbia.edu/" target="_blank">applied physics</a>. &ldquo;Until now, it&rsquo;s been impossible to shrink and mass-deploy technologies that require tunable and narrow-linewidth visible lasers. A notable example is quantum optics, which demands high-performance lasers of several colors in a single system. We expect that our findings will enable fully integrated visible light systems for existing and new technologies.&rdquo;&nbsp;<blockquote>What&rsquo;s exciting about this work is that we&rsquo;ve used the power of integrated photonics to break the existing paradigm that high-performance visible lasers need to be benchtop and cost tens of thousands of dollars.<footer>MATEUS CORATO ZANARELLA</footer><footer>LEAD AUTHOR OF THE STUDY AND PHD STUDENT IN THE LIPSON NANOPHOTONICS GROUP</footer></blockquote><section id="isPasted"><h2>Benefits of emitting wavelengths below red</h2>The importance of lasers emitting wavelengths shorter than red is clear when you consider some important applications. Displays, for example, require red, green, and blue light simultaneously to compose any color. In quantum optics, green, blue, and violet lasers are used for trapping and cooling atoms and ions. In underwater Lidar (Light Detection and Ranging), green or blue light is needed to avoid water absorption. However, at wavelengths shorter than red, the coupling and propagation losses of photonic integrated circuits increase significantly, which has prevented the realization of high-performance lasers at these colors.&nbsp;<h2>Solving coupling and propagation loss issues</h2>The researchers solved the coupling loss problem by choosing Fabry-Perot (FP) diodes as the light sources, which minimizes the impact of the losses on the performance of the chip-scale lasers. Unlike other strategies that use different types of sources, the team&rsquo;s approach enables the realization of lasers at record-short wavelengths (404 nm) while also providing scalability to high optical powers, FP laser diodes are inexpensive and compact solid-state lasers widely used in research and industry. However, they emit light of several wavelengths simultaneously and are not easily tunable, preventing them to be directly used for applications requiring pure and precise lasers. By combining them with the specially designed photonic chip, the researchers are able to modify the laser emission to be single-frequency, narrow-linewidth, and widely tunable.&nbsp;The team overcame the propagation loss issue by designing a platform that minimizes both the material absorption and surface scattering losses simultaneously for all the visible wavelengths. To guide the light, they used silicon nitride, a dielectric widely used in the semiconductor industry that is transparent for visible light of all colors. Even though there is minimal absorption, the light still experiences loss due to unavoidable roughness from the fabrication processes. The team solved this problem by designing a photonic circuit with a special type of ring resonator. The ring has a variable width along its circumference, allowing for single-mode operation characteristic of narrow waveguides, and low loss characteristic of wide waveguides. The resulting photonic circuit provides a wavelength-selective optical feedback to the FP diodes that forces the laser to emit at a single desired wavelength with very narrow linewidth.&ldquo;By combining these intricately designed pieces, we were able to build a robust and versatile platform that is scalable and works for all colors of light,&rdquo; said Corato Zanarella.&nbsp;<h2>Revolutionizing technologies</h2>&ldquo;As a laser manufacturer we recognize that integrated photonics will have a tremendous impact on our industry and will enable a new generation of applications that have so far been impossible,&rdquo; said Chris Haimberger, director of Laser Technology, TOPTICA Photonics, Inc. &ldquo;This work represents an important step forward in the pursuit of compact and tunable visible lasers that will power future developments in computing, medicine, and industry.&rdquo;The study&rsquo;s findings could revolutionize a broad range of applications, including:</section><section><a href="https://www.engineering.columbia.edu/news/high-performance-visible-light-lasers-fit-fingertip#" target="_blank"><ul><li> Quantum information</li></ul></a></section><section><a href="https://www.engineering.columbia.edu/news/high-performance-visible-light-lasers-fit-fingertip#" target="_blank"><ul><li>&nbsp;Atomic Clocks</li></ul></a></section><section><a href="https://www.engineering.columbia.edu/news/high-performance-visible-light-lasers-fit-fingertip#" target="_blank"><ul><li>&nbsp;Biosensing</li></ul></a></section><section><a href="https://www.engineering.columbia.edu/news/high-performance-visible-light-lasers-fit-fingertip#" target="_blank"><ul><li>&nbsp;Underwater Ranging</li></ul></a></section><section><a href="https://www.engineering.columbia.edu/news/high-performance-visible-light-lasers-fit-fingertip#" target="_blank"><ul><li style="font-weight: bold;">&nbsp;Li-Fi</li></ul></a></section><section><h2>Next steps</h2>The researchers, who have filed a provisional patent for their technology, are now exploring how to optically and electrically package the lasers to turn them into standalone units and use them as sources in chip-scale visible light engines, quantum experiments, and optical clocks.&ldquo;In order to move forward, we have to be able to miniaturize and scale these systems, enabling them to eventually be incorporated in mass-deployed technologies,&rdquo; said Lipson, a pioneer in silicon photonics whose research has strongly shaped the field from its inception decades ago, with foundational contributions in the active and passive devices that are part of any current photonic chip. She added, &ldquo;Integrated photonics is an exciting field that is truly revolutionizing our world, from optical telecommunications to quantum information to biosensing.&rdquo;</section>

Illustration of the integrated laser platform created by the Lipson Nanophotonics Group, where a single chip generates narrow linewidth and tunable visible light covering all colors. Credit: Myles Marshall/Columbia Engineering

In a significant advance for impactful technologies such as quantum optics and laser displays for AR/VR, Columbia Engineering’s Lipson Nanophotonics Group has invented the first tunable and narrow linewidth chip-scale lasers for visible wavelengths shorter than red.

High-performance Visible-light Lasers that Fit on a Fingertip

Printing objects from plastic precisely, quickly, and inexpensively is the goal of many 3D printing processes. However, speed and high resolution remain a technological challenge. A research team from the Karlsruhe Institute of Technology (KIT), Heidelberg University, and the Queensland University of Technology (QUT) has come a long way toward achieving this goal. It developed a laser printing process that can print micrometer-sized parts in the blink of an eye. The international team published the work in&nbsp;Nature Photonics. (DOI:&nbsp;<a href="https://www.nature.com/articles/s41566-022-01081-0" target="_blank">10.1038/s41566-022-01081-0</a>)Stereolithography 3D printing is currently one of the most popular additive manufacturing processes for plastics, both for private and industrial applications. In stereolithography, the layers of a 3D object are projected one by one into a container filled with resin. The resin is cured by UV light. However, previous stereolithography methods are slow and have too low a resolution. Light-sheet 3D printing, which is used by the KIT researchers, is a fast and high-resolution alternative.<h2>3D Printing with Two Colors in Two Stages</h2>In light-sheet 3D printing, blue light is projected into a container filled with a liquid resin. The blue light pre-activates the resin. In a second stage, a red laser beam provides the additional energy needed to cure the resin. However, 3D printing can only print quickly resins that quickly return from their pre-activated state to their original state. Only then can the next layer be printed. Consequently, the return time dictates the waiting time between two successive layers and thus the printing speed. &quot;For the resin we used, the return time was less than 100 microseconds, which allows for high printing speeds,&quot; says first author Vincent Hahn from KIT&#39;s Institute of Applied Physics (APH).<h2>Micrometer-sized Structures in Just the Blink of an Eye</h2>To take advantage of this new resin, the researchers built a special 3D printer. In this printer, blue laser diodes are used to project images into the liquid resin using a high-resolution display with a high frame rate. The red laser is formed into a thin &quot;light sheet&quot; beam and crosses the blue beam vertically in the resin. With this arrangement, the team was able to 3D print micrometer-sized parts in a few hundred milliseconds, i.e. in the blink of an eye. However, it should not stop there: &quot;With more sensitive resins, we could even use LEDs instead of lasers in our 3D printer,&quot; says Professor Martin Wegener of APH. &quot;Ultimately, we want to print 3D structures that are centimeters in size, while maintaining micrometer resolution and high printing speeds.&quot;The publication was produced within the framework of the joint &ldquo;3D Matter Made to Order&rdquo; Cluster of Excellence of the KIT and Heidelberg University. Junior Professor Dr Eva Blasco, a group leader at the Institute of Organic Chemistry and the Institute for Molecular Systems Engineering and Advanced Materials, was involved on the part of Heidelberg University.Original Publication: V. Hahn, P. Rietz, F. Hermann, P. M&uuml;ller, C. Barner-Kowollik, T. Schl&ouml;der, W. Wenzel, E. Blasco, and M. Wegener: Light-sheet three-dimensional microprinting via two-colour two-step absorption. Nature Photonics, 2022. DOI: 10.1038/s41566-022-01081-0 <a href="https://www.nature.com/articles/s41566-022-01081-0" target="_blank">https://www.nature.com/articles/s41566-022-01081-0</a><h2>Cluster of Excellence &quot;3D Matter Made to Order&rdquo;</h2>In the Cluster of Excellence &quot;3D Matter Made to Order,&quot; scientists from the Karlsruhe Institute of Technology (KIT) and Heidelberg University are conducting interdisciplinary research on innovative technologies and materials for digitally scalable additive manufacturing to improve the precision, speed, and performance of 3D printing. The goal of the work is to fully digitize 3D manufacturing and materials processing from the molecule to the microstructure. In addition to being funded as a Cluster of Excellence under the Excellence Strategy Competition of the German federal and state governments, &quot;3D Matter Made to Order&quot; is funded by the Carl Zeiss Foundation.Read more on the Cluster of Excellence<a href="https://www.3dmattermadetoorder.kit.edu/" target="_blank">&nbsp;&bdquo;3D Matter Made to Order&ldquo;</a><a href="https://www.materials.kit.edu/index.php" target="_blank">Details on the KIT Center Materials in Technical and Life Sciences</a>

In light sheet 3D printing, red and blue laser light is used to print objects precisely and quickly on a micrometer scale (Photo: Vincent Hahn, KIT)

Researchers from the Cluster of Excellence "3D Matter Made to Order" Print Microstructures by Crossing Red and Blue Laser Beams - Publication in Nature Photonics

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