Laser 3D Manufacturing XII

Since the groundbreaking achievement of ignition and self-sustaining fuel burn at the U.S. National Ignition Facility (NIF), the field of fusion, specifically laser inertial fusion energy (IFE), has rapidly accelerated and transformed. Numerous countries are investing more heavily or initiating new fusion programs, with significant collaborative efforts from international research institutions and the private sector accelerating the path to practical fusion energy. The implications for the photonics market include an increased demand for lasers, optics, optical materials, diagnostics, and other key technologies, creating new opportunities for photonics companies and shifting market dynamics. Future challenges and strategies for achieving higher energy yields and commercial viability are outlined, emphasizing the critical role of photonics in enabling the next generation of fusion energy solutions.

The interaction of light and matter can create bonding structural and morphological changes in nano/micro-scale from the surfaces of diverse materials, sometimes even deep within them. This feature has been utilized in laser processing to produce new value for both science and industry. Recent advances in high-power, ultrashort pulsed laser and fast beam delivery technologies are rapidly expanding the possibilities of laser processing. At the same time, the number of parameters to be controlled has become enormous, which is why we have introduced Data Science. In this talk, we will discuss new data-driven laser processing utilizing high-speed data acquisition and AI data optimization for higher throughput and quality. We also aim for this technology to contribute to sustainable manufacturing and society in the future.

Optical frequency combs have revolutionized time and frequency metrology by providing rulers in frequency space that measure large optical frequency differences and/or straightforwardly link microwave and optical frequencies. One of the most successful uses of frequency combs beyond their original purpose has been dual-comb interferometry. An interferometer can be formed using two frequency combs of slightly different line spacing. Dual-comb interferometers without moving parts have no geometric limitations to resolution, therefore miniaturized devices using integrated optics can be envisioned. Dual-comb interferometers outperform state-of-the-art devices in an increasing number of fields including spectroscopy and holography, offering unique features such as direct frequency measurements, accuracy, precision, and speed.

Today, approximately 12,000 satellites orbit Earth. By 2030, estimates show numbers above 60,000. Today, we service spacecraft when absolutely necessary. By 2030’s, in-space services will be routine; refueling, repair, relocation, assembly, and manufacturing. Advances are underway to realizing this future, enabling a sustainable version will require photonics technologies.

The study showcases the evolution and versatility of two-photon absorption (2PA) in 3D printing. Using the in-situ material exchange system MergeOne system, we successfully fabricated diverse structures and analyzed laminar flow dynamics with fluorescence microscopy. Computational flow dynamics simulations confirmed the observed behavior. We demonstrated lateral multi-material micro-lens printing, along with precise control over material exchange and polymerization parameters. This approach enhances design flexibility and functionality, particularly in additive manufacturing, marking significant advancements in commercial 2PA technology.

3D laser-printed microstructures often differ from the intended models due to various mechanisms, such as dose accumulation, shrinkage, or unintended printing below the substrate. So far, the deviations between the intended model and the ex-situ characterization result had to be compensated iteratively, leading to a tedious feedback loop. Here, we present a novel deep learning-driven in-situ tomographic reconstruction technique based on stacks of widefield optical intensity images taken during the printing process. A deep neural network is trained to reconstruct specimens by simulated optical intensity images. The reconstruction before development during the printing process itself can drastically accelerate material design and characterization.

The rapidly developing frontiers of additive manufacturing, especially multi-photon lithography, create a constant need for optimization of new process parameters. The recently developed projection multi-photon lithography process used in this work is one such example. This work presents an active machine learning framework which can serve as a guide for exploration of these uncharted parameter spaces. The framework uses Bayesian optimization to guide experimentation to dynamically collect the most optimal data for training of a Gaussian process regression machine learning model. This model then serves as a surrogate for the manufacturing process by predicting optimal process parameters for printing of a target geometry. The results of the framework for several 2D shapes are shown and the extension of this framework to 3D structures is discussed.

In this work we demonstrate the capabilities of our diode laser based multi-photon polymerization (MPP) system, which aims at significantly reducing the required investment compared to available machines. While currently available systems rely on ultra short optical pulses from fibre lasers or titanium Sapphire lasers, we employ monolithically mode-locked diode lasers at a repetition rate of 6 GHz and emission wavelength around 780 nm to induce the polymerization process. These lasers allow for direct switching of the gain current and do therefore not require additional fast shutters. Overall, this results in a cost effective and compact machine that can work with conventional resins for MPP without any further adaption to our system. We will introduce our system, show the properties of the used diode lasers and demonstrate the manufacturing capabilities.

Micro and nanoscale additive manufacturing using projection multi-photon lithography has the potential to print 3D structures at high speeds. Optimizing parameters for precise 2D layer printing by trial and error requires time-consuming and costly methods. This study introduces a convolutional neural network machine learning scheme to optimize printing using a fast and inexpensive data collection method. By training autoencoders with input patterns and optical microscope images, we can visualize how printed layers would look and explore input layer pattern generation from an inverse model, significantly reducing time and cost in achieving precise micro-nanoscale 3D printed structures.

The ultimate dream of 3D laser nanoprinting is to manufacture arbitrary macroscopic complex 3D structures with nanometer feature sizes by exposing an ink with a single femtosecond laser pulse. We argue that the corresponding light fields can be shaped by optical holography, which literally allows to print at the speed of light. We further argue that currently available single-box regeneratively amplified femtosecond lasers with mJ pulse energy, 100-fs pulse duration, 800-nm wavelength, and 1-10 kHz repetition rate together with multi-photon absorption should allow for exposing 3D objects containing 10^8 to 10^9 voxels within one picosecond, leading to peak print rates of 10^20 to 10^21 voxel/s. Such values would surpass the current best peak print rates of about 10^8 voxel/s by a very large margin. We give an introduction and review steps in this direction by other groups.

Two-photon 3D laser printing has been established as an excellent tool for precise micro- and nanoscale fabrication with applications in a wide range of fields. The properties of 3D printed microstructures strongly depend on material formulation and printing parameters. Comprehensive understanding and systematic characterization methods are crucial for successful integration of the developed materials into real-world applications. The lack of standardized procedures and control of the (macro)molecular architecture of the printing formulations remains a challenge. In recent studies, we demonstrate that the combination of defined (macro)molecular printable materials and systematic characterization methods at the microscale is critical for materials design.

Since the latest ISO 25178 publication, calibration of areal measuring instruments has been fully documented, emphasizing its importance all over. We previously highlighted the advantages of direct laser written calibration structures, such as design freedom, high resolution, and thermal stability, leading to an universal calibration artifact for all ISO-based metrological characteristics. Now, we report on extensive international comparison measurements to apply multiscale analysis (MSA) to direct laser written structures for the first time. Generally, MSA characterizes surface topographies across several scales, crucial when calibration standard and measuring device operate on different size scales. Specifically, areal and volumetric analysis methods were used to investigate the transfer behaviour of areal measuring instruments. We found a clear correlation between MSA results and ISO-conform metrological characteristics, linking scale-dependent transfer behaviour, resolution limits, and the ability to capture large surface angles. These findings suggest that MSA enhances performance verification and uncertainty determination of areal surface topography measuring instruments.

In this work, we propose a new alternative to perform the true 3D alignment of liquid crystal elastomers (LCEs) in a precise manner compatible with 3D direct laser writing (3D DLW). By playing both on the orientation strategy and the fabrication parameters, different deformations can be programmed starting from a single CAD model. A collection of building block is first demonstrated, then assembly of these building block is achieved, leading to 3D micro-objects presenting sophisticated behaviour. Finally, the fine control offered by our approach is illustrated i) by building a micro-actuator and investigating its performance ii) by elaborating miniaturized colorimetric sensors.

The recent implementation of two-step photoinitiators (Nat. Photon. 15, 932-938 (2021)) for three-dimensional nanoscale direct laser writing has enabled printing with low cost, low power laser diodes while preserving the nonlinear relationship between printing and incident light intensity found in two-photon absorption. Thus far, this method has been able to achieve very high printing resolutions at the diffraction-limit. In order to further improve this resolution, we implement a photoinhibition scheme inspired by stimulated emission depletion (STED). Similar schemes have previously been used in two-photon absorption-based printing and have successfully demonstrated printing resolutions beyond the diffraction limit. Thus, in this work we use a novel, depletable, two-step photoinitiator to combine two-step printing with STED-inspired techniques and achieve sub-diffraction limited printing resolution in a compact, stable optical setup.

The development of a novel method for patterning functional structures on hydrogels via laser scanning promises to facilitate the fabrication of hydrogel-based electric or optical devices. This presentation will outline our studies focused on directly patterning functional microstructures on hydrogels using laser technology. In the first part of the presentation, we will discuss our investigation into fabricating metal microstructures within hydrogels through multi-photon photoreduction. By integrating locally imparted optical properties with inherent hydrogel characteristics, applications such as plasmonic sensing, soft actuators, and optical switching become feasible. In the latter part of the presentation, we will introduce our research on laser-based graphitization applied to hydrogels. While hydrogels were considered challenging for laser-induced graphitization, we have successfully achieved to pattern graphitic carbon structures on hydrogels. We will describe the fabrication method and discuss applications utilizing the conductive structures in hydrogel-based supercapacitors and microstrip antennas.

Protein-based 3D nano-scaffolds are crucial for modern tissue engineering, offering biocompatible and biodegradable support for tissue development. Multiphoton Lithography (MPL) allows rapid prototyping of these scaffolds with sub-1µm features and tuneable mechanical properties. Unlike synthetic polymers, protein-based materials possess inherent biofunctionality, although the impact of photodamage of the proteins during MPL is under-investigated. In this contribution, we used methacrylated proteins mixed with a vitamin-based photoinitiator to explore the impact of methacrylation, residual absorption, and reactive oxygen species on the polymerization threshold and protein functionality after printing. The research is vital for developing protein-based materials for biomedical applications.

Bioprinting, especially using Laser Induced Forward Transfer (LIFT), shows significant potential for creating living tissues by precisely printing cells and biomaterials. This technique fabricates structures that mimic native tissue functions, useful in regenerative medicine. In this study, various cell-laden bioinks were printed with LIFT, utilizing a Nd:YAG laser at 532nm to create ex vivo 3D structures. Detailed rheological characterization and optimized laser parameters ensured accurate cell depositions. Mouse-derived urothelial and smooth muscle cells were printed within biomaterials like Platelet Lysates methacrylated (PLMA) and hydrogels, forming a 3D bladder graft. LIFT bioprinting demonstrates significant advantages for controlled tissue fabrication.

By a multi-focus multi-photon 3D laser microprinting setup, which prints considerably faster than 3D printers based on only a single focus, in combination with a very sensitive multi-photon resist, we have been able to fabricate various macroscopic structures, as well as huge amounts of microscopic particles for different applications. The applications range from nanolattices with a very high strength-to-mass ratio and biological microswimmers to particles for respiratory research. Centimeter-sized samples as well as millions of multiple-micrometer sized particles could be fabricated in only hours to days.

In 3D bioprinting, photopolymerization is vital for constructing layered structures, with parameters like light intensity and exposure time significantly affecting cell viability and construct quality. This study examines how varying these parameters impacts 3T3 fibroblast viability, proliferation, and morphology in GelMA and GelMA-PEGDA bioinks. Results show that longer exposure times and higher light intensities reduce cell viability, while shorter exposure times and lower intensities support better cell health. After optimizing these conditions, a bronchi branch was successfully bioprinted, demonstrating the importance of fine-tuning photopolymerization for effective biofabrication.

This presentation will include two research projects conducted at Syracuse University and few outreach slides related to opportunities at NSF for the Additive Manufacturing community. First project, entitled, Multi-material Gradient Printing Using Meniscus-enabled Projection Stereolithography (MAPS) addresses current challenges related to vat based multi-material printing associated with hardware modifications, control systems, cross-contamination, waste, and resin properties. We show that MAPS can print 3D structures with gradient properties in mechanical stiffness, opacity, surface energy, cell densities, and magnetic properties. Second project, entitled Multipath projection stereolithography (MPS) addresses the inherent tradeoffs between print resolution, design complexity, and built sizes. Inspired by microscopes that could switch objectives to achieve multiscale imaging, we report a new optical printer coined as MPS specifically designed for printing microfluidic devices. Using a test-case of micromixers, we show user-defined CAD models can be directly input to an automated slicing software to define printing of low-resolution features with embedded microscale fins.

Two-step-absorption 3D laser nanoprinting is an attractive alternative to its multi-photon-absorption counterpart as it allows for using compact and cost-efficient continuous-wave laser sources. Given that single-focus laser powers are typically below 1 mW, multi-focus parallelization is a viable approach to increase print speed while still relying on compact continuous-wave laser sources. We combine an established photoresist system for two-step-absorption 3D laser nanoprinting with a multi-focus approach based on binary holography. For this purpose, a digital micromirror device (DMD) is used as a beam-splitting and beam-steering device. This allows for the individual control of each laser focus within the print plane.

Two-photon polymerization (TPP) has emerged as an exceptional 3D fabrication tool for tissue engineering and regenerative medicine. Constructs fabricated using TPP can be further enhanced by functional particles or cells to improve their targeted applications. This enhancement can be achieved through the combination of TPP using femtosecond lasers, and optical tweezers (OT) using continuous wave (CW) laser sources. However, this complicates the optical alignment; additionally, conventional CW-OT requires high intensity which poses risks of photodamage to heat-sensitive components. In this study, we demonstrate an integrated platform using the same ultrafast laser source for fabrication and manipulation of 3D microstructures without inducing thermal damage.

To transition additive manufacturing from a rapid-prototyping role to at-scale production, commercial resin-based printers have pushed towards 1 meter-per-hour printing speed by synergizing area projection and continuous stage motion. To push this further, we present a continuous 3D-printing method using a lubricated textured membrane – dubbed TEMPO - to achieve a 100-fold improvement in speed over the current state-of-the-art. These high-speeds have elucidated a breakdown in the traditional working curve model, as the speed-accuracy trade-off shifts from supply-limited to reaction limited. The versatility of the lubricant layer allows the user to tailor TEMPO for printing speeds of up to 3 cm/s, resolutions down to 1.76um for freestanding features, and viscous and scattering, high-performance polymers with minimal considerations to the physical limitations of the printing window.

Computational illumination using a programmable LED array is a powerful, simple, and inexpensive method to enhance microscopy. Techniques like differential phase contrast and Fourier ptychography have been demonstrated for 2D and 3D enhanced imaging. In this work, we utilise these techniques for quality control, monitoring and feedback control of precision laser processing (PLP) processes. This approach benefits from no moving parts and easy integration, relying on computational methods and computer vision techniques. By merging theoretical development with practical application, we showcase the effectiveness of these techniques in industrial settings to suit several laser manufacturing needs.

Microsupercapacitors (MSCs) are crucial micropower sources due to their rapid charging/discharging and miniatured size. Numerous efforts have been made to develop 3D MSCs, mainly by designing a 3D homogeneous architecture design where active materials are predominantly constructed on an existing current collector. This study successfully fabricates 3D current collector electrodes using laser-based directed energy deposition. A metal current collector with a scaffold of three arrays of 27 high-aspect-ratio (∼14) Inconel 625 micropillars (110 µm diameter) are printed on a stainless-steel substrate, serving as a framework for active material storage. The metallic current collector is then coated with active electrode materials, resulting in significantly increased capacitance and enhanced electrolyte penetration, highlighting its potential for future applications.

Laser-based 3D printing, especially two-photon polymerization (2PP), is effective for creating sub-wavelength structures with applications in photonics, nanofluidics, NEMS, drug delivery, and tissue engineering. Traditionally, 2PP uses compound refractive lenses for precise light focusing. This work introduces an alternative using optical metalenses, which enhances 2PP's versatility and precision. By custom-tailoring the metalens point spread function, more complex geometries can be fabricated. We integrated metalenses into a custom 2PP system, experimentally validating this with 3D polymer microstructures. This advancement in 2PP technology allows for more intricate and sophisticated nanomanufacturing applications.

High-resolution Digital Light Processing (DLP) bioprinting requires precise control over photocrosslinking, particularly for complex models with fine gaps. This study presents a novel segmentation approach that utilizes the DLP system's diffusion characteristics, avoiding alterations to core components. The method segments the photomask into discrete regions and employs an on-off activation strategy to regulate the distribution and concentration of free radicals, enabling printing with 100 µm gaps between bronchial branches at a 14.43x compression ratio. Demonstrated by printing a bronchial model with intricate structures, the approach achieved up to 90% cell viability for GelMA and 85% for GelMA-PEGDA over seven days.

The gap between the rotor and stator of an axial flux motor for electric vehicles must be measured extremely precisely in order to guarantee a specific distance when assembling the motor. A freeform micro-optic was designed and printed by means of two-photon polymerization. The gap was measured by printing the optics onto the fiber of an optical coherent tomography (OCT) device. The results show that the 3D-printed fibre probes allow the measurement of geometries with high aspect ratios and high accuracy. In the talk the optical design, fabrication and results of 3D printed micro-optics for optical coherence tomography fibre probes will be discussed.

A controllable and cost-effective optical printing system was developed using a Digital Micromirror Device (DMD) for the rapid fabrication of photosensitive polymers. This system supports a wide range of materials and allows for the customization of microstructures, making it a versatile platform for physical, chemical, and biological sensing applications. High-resolution hydrogel sensors, based on poly(2-hydroxyethyl methacrylate) (PHEMA), were fabricated for alcohol detection. These sensors exhibited significant changes in diffraction efficiency upon alcohol exposure, with low detection limits, fast response times, and excellent repeatability.

In this study, we demonstrate the application of a laser-based multi-wavelength dark-field scattering technique for the surface analysis of powder-based additive manufacturing (AM) processes. Our experiments encompass a variety of materials commonly used in powder-based AM, providing a comprehensive assessment of the method's versatility. We detail the technique's efficacy in analyzing surface roughness, a critical factor affecting the mechanical properties and performance of AM parts. The results indicate that our approach can detect subtle, µm-sized variations in surface texture, offering a robust tool for improving the quality control and optimization of AM processes. The results showed that an axial resolution of down to 3 µm at a height range of multiple millimeters is achievable. The scanning of large areas with a size of 200 x 500 mm² can be performed at frame rates surpassing 100 fps. This method presents a significant advancement in the precision and applicability of surface analysis techniques in additive manufacturing, ensuring better control over the fabrication process and resulting in higher-quality end products.

M-LMD is a technology that simultaneously causes the melting of the supplied powder material and the substrate material, and powder and substrate material are melted and welded. Therefore, it is possible to form a dense coating with little heat effect on the base material and little dilution. Because pure copper coating is material that physical properties significantly change in dilution, so it is important to reduce the dilution layer between substrate and copper coating. Depending on the substrate materials, dilution layer changes, and therefore the properties of the pure copper coating also change. So, in this study, SUS304, Al, and copper alloys plate were used different light absorption rates. And pure copper coating was formed on these materials using B-M-LMD. Observation of cross-sectional was performed, and the dilution layer was evaluated.

A novel Spatial Frequency Modulation Imaging (SPIFI) optical metrology system is coupled to a laser powder bed fusion (PBF-LB) system for the first time. Significantly, SPIFI records images with a photodiode and produces enhanced resolution. Real-time SPIFI images of melt tracks using 316L steel powder are demonstrated as a function of delay with respect to the fusing beam. Metrics of performance for the SPIFI system in this configuration are presented.

Conventional laser-based powder bed fusion (PBF-LB/M) for fabricating 3D metal parts requires support structures to secure the printed parts to a baseplate. However, these support structures often decrease printing efficiency and limit design freedom. In this study, a novel method to substantially reduce the thermal residual stresses produced during the PBF process has been developed by combining focused in-situ infrared (IR) heating with conventional techniques. The reduced stress enables the fabrication of high-aspect-ratio Ti-6Al-4V thin walls and 0-degree overhang beams, which cannot be printed using conventional processes. Furthermore, this method allows for support-free printing of various 3D parts, including a level-2 Menger sponge and a hollow honeycomb cylinder. In the novel process, the IR-heated powder, with loose consolidation, functions as both a support structure to withstand internal thermal stresses and external impacts and as a heat sink. The IR-consolidated powder can be easily removed from the printed part and reused.

The additive manufacturing industry has a current and ever-emerging need for in-process monitoring, dynamic feedback, and timely control from a scan head designed for laser powder bed fusion within the metal additive space. To be considered a viable solution to this problem, any system must take into consideration its total value proposition to the end user. Considerations such as ease of integration, increased throughput, reduced risk against downtime, and scrap rates from poor part quality must also be addressed.

Laser-based Directed Energy Deposition (DED) is an industrially established AM process that is used for a variety of different contours, surfaces, repair and redesign purposes as well as the construction of complete components. The challenge here is that components become more and more complex, larger and therefore more difficult to build. This means that sometimes lengthy processes have to be carried out in a very robust, reproducible and cost-effective manner. In contrast to conventional production technology, numerous dynamic process influences and weld pool phenomena have a decisive influence on the resulting welding result in DED. Precise attention must therefore be paid to exact temperature-time curves, suitable path planning and suitable solidification conditions in order to achieve a tightly toleranced contour accuracy of the resulting component and to obtain defect-free results. During this lecture, different control approaches will be presented in order to come closer to the aforementioned goal. In addition to a variety of sensors and customized process tools, this can also be supported by the use of AI-based methods.

Refractory metals are used in applications requiring extreme high temperature-resistance, e.g. jet propulsion systems in aerospace applications or for controlling nuclear reactions. However, the traditional manufacturing of these metals is demanding and expensive, especially if fine structures are required. Here, we report on the laser assisted powder bed fusion of pure Molybdenum. The high melting point and thermal conductivity together with a high susceptibility to solidification fractures make it difficult to identify a suitable parameter window for the laser-based melting process using standard continuous wave laser systems. Thus, we apply an ultra-short pulse laser system operating at a center-wavelength of 1030nm and a repetition rate of 32,5MHz with a pulse width of around 260fs for the additive processing. Using the additional parameter field provided by the pulsed laser source, we are able to fabricate thin-walled structures well below 70µm as well as volumetric parts with a relative density close to 100%.

Laser powder bed fusion (L-PBF) is an advanced manufacturing process with slow build rates. Increasing laser power using conventional Gaussian beams leads to high peak intensities, causing material defects. Solutions include defocusing the laser beam within the Rayleigh length and using beam-shaping technologies like Multi-Plane Light Conversion (MPLC). MPLC can switch beam shapes, enhancing printing speeds and quality. This method achieved a 3.3-fold speed increase for nickel alloy 625, with improved mechanical performance confirmed by tests.

In Laser Powder Bed Fusion (LPBF), process productivity, stability and quality depend to a large extend on the intensity distribution used. While the latest developments in optical components allow for spatial and temporal intensity distributions with a large amount of degrees of freedom, it is difficult to determine advantageous intensity distributions within this large parameter space. In this work, a reduced process model is presented that allows for determining such intensity profiles by solving an inverse heat conduction problem for the LPBF process. For this purpose, advantageous temperature profiles are derived from the requirements for the melt pool geometry and used as target variables for the inverse calculation. The resulting intensity profiles are then discussed with regard to their experimental feasibility.

In the laser powder bed fusion (LPBF) process, only a fraction of powders ultimately undergo full melting and contribute to the formation of the final parts. Here, we define powder melting efficiency as the ratio of the deposited track mass to the mass of powder consumed. We investigate the influence of process parameters and alloy properties on powder melting efficiency using stainless steel 316 and Ti6Al4V powders. We find that powder melting efficiency can be improved by increasing laser power or reducing scanning speed and layer thickness. Under the same process condition, Ti6Al4V alloy exhibits higher powder melting efficiency compared to stainless steel 316. Multiple powder melting efficiency maps are generated under various process conditions for two alloys. In addition, we derive a dimensionless powder melting index to represent the ratio of the volumetric energy input to the energy required to melt per unit mass powder. Both the powder melting efficiency maps and dimensionless index can help optimize process conditions for printing high-quality parts economically.

This study explores the development of a take-home device for monitoring TMD symptoms using 3D printing and accelerometry. Nightguard prototypes are modeled and printed with biocompatible resins, incorporating accelerometers to track jaw movements. A 3D-printed denture model simulates jaw movements for testing. Extensive testing ensures accuracy and reliability. This proof-of-concept study aims to establish feasibility for future clinical trials, integrating AI for data analysis and optimizing fabrication methods to validate efficacy and user requirements.

A CO2 laser additive manufacturing technique for depositing transparent thick TiO2 films on quartz substrates is reported. Thick TiO2 films are prepared in three stages, i.e., wet deposition using the spin-coating technique, evaporation of liquid using a lamp, and CO2 laser-assisted sintering of nanoparticles (NPs) to form a transparent film. A heat transfer model is presented for laser processing parameter selection. Different concentrations of anatase TiO2 suspensions are used to control the thickness and adjust the optical properties. SEM revealed that the absorbed CO2 laser energy promotes the formation of necking and coalescence between TiO2 NPs. A transmittance above ~85% can be achieved in some visible and IR ranges. A minimum reflectance can be achieved by controlling the sintering power and TiO2 concentration. The effect of laser power on morphological and optical properties is reported. The effects of TiO2 concentration on the refraction and absorption indices are investigated. Raman analysis is carried out to give a better insight into film microstructures. XRD analysis revealed that the sintered films are preserved as anatase TiO2.

In this work, we demonstrate the application of laser induced forward transfer (LIFT) of metal nanoparticle inks and pastes for the additive manufacturing micro-electrodes and laser soldering of solder paste onto SiO2/Si substrates, in order to bond micro-components on photonic chips. Preliminary results were promising, in the combination of solder paste LIFT and laser soldering achieving the bonding of a capacitor on silicon substrates from a mechanical point of view.

The tensile property of 3D printed polymers is found to be both process-dependent and size-dependent. And therefore, to accurately characterize hundred-micron features made by stereolithography in applications like vascular stent, miniaturized specimens fabricated at the device-relevant dimensional scale using the same conditions are required. To achieve gage displacement measurement without introducing errors from physical contact, we developed a numerical algorithm based on a 1D mechanical model of the specimen in tensile process to estimate gage displacement from the total displacement measured via grip distance for miniaturized specimen and calculate the whole stain-stress curve from it. The algorithm has been thoroughly tested and validated through both experiment and FEM simulation, shows a maximum relative error under 6%. And the total wall time for each run only takes 3.034 seconds on a normal laptop. Its efficiency and accuracy indicate its potential in rapid characterizing new-developed polymers and help improve fine-feature devices.

Two-photon grayscale lithography (2GL®), which is the two-photon polymerization (2PP) laser-printing with power modulated dynamic size control over the polymerized voxels, has demonstrated unprecedented combinations of pristine structure quality and high throughput. However, the technique has so far only been demonstrated to manufacture polymer microstructures. Herein, we present a 2GL® fabrication route to print optical-grade silica glass micro- & nanostructures from our recently introduced pre-glass resin system, which is based on polyhedral oligomeric silsesquioxane (POSS) chemistry. The POSS resin is shown to print pre-glass templates via 2GL® with sharply resolved features and minimal surface roughness at print speeds of hundreds of millimeters per second. Moderate thermal treatment at 650°C in air atmosphere drives-off the material’s organic parts and converts the templates to high-quality silica glass structures. We demonstrate a spectrum of glass benchmark structures with varying complexity and sizes and discuss adjusted chemical formulations for high-speed printing with minimal artefacts.

Microlens arrays (MLAs) are commonly used in various applications including beam shaping, illumination optics, fiber light coupling and imaging. Here, we investigate unconventional techniques to produce glass MLAs with unique arrangements and different lens properties. We present a laser-assisted manufacturing method combining femtosecond laser machining of preform shapes, wet etching and laser thermal reflow to achieve low surface roughness’s and targeted lens curvatures. This technique has high design flexibility, allowing for manufacturing of multifocal lens-array (MFLA), enabling 3D imaging as well as a novel approach for skewed optics, for light redirection and field-of-view (FOV) enhancement. This process paves the way for more complex freeform shapes in glass and manufacturing of highly tuneable MLAs optimized for applications such as integral imaging or compound eyes.

The development of visible-light optical coherence tomography (vis-OCT) has revolutionized the precision in measuring 3D anatomic features. When combined with 3D printing, which efficiently converts digital models into tangible objects, both technologies achieve micron-scale resolution. This synergy opens new avenues in designing and creating custom biomedical devices tailored to individual patients. For instance, in the case of contact lenses, vis-OCT is utilized to accurately map the corneal surface topology. This mapping informs the design of the contact lens's inner surface, ensuring an optimal fit. Subsequently, these personalized contact lens designs are produced using advanced, high-resolution 3D printing techniques. Both the fit and optical performance of these 3D-printed contact lenses have been thoroughly tested and validated experimentally

Two-photon-lithography (TPL) is a powerful nano-3D printing technique known for leveraging non-linear absorption to enable sub-micron printing resolution. However, the throughput of TPL is limited owing to its single laser spot scanning mechanism and the limited field-of-view of conventional microscope objectives. We present a novel parallelized TPL platform that replaces the single high-NA objective with a large array of high-NA, polymer immersion metalenses. Independent control over the focusing intensity from each metalens is achieved using a spatial light modulator (SLM) to modulate the intensity of each metalens focusing spot, enabling the large scale writing of periodic and aperiodic patterns with time scales and stitching errors that exceed the capabilities of conventional platforms.

Optical vortices (OVs) find applications in various fields including high-order quantum entanglement, optical tweezers, astrometry, medicinal applications, and nonlinear optics. However, traditional passive methods for generating OVs, such as custom synthetic holograms, spiral wave plates, double cylindrical lens phase converters, light scattering from uneven surfaces, and interference of regular waves, often produce single-mode OVs or lack adjustability and flexibility. Here, we introduce an innovative, fully characterized, passively tunable device for generating optical vortices. This device is fabricated using 3D femtosecond direct laser writing (3D fs-SLW) techniques and incorporates a three-dimensional pattern of silver microstructures embedded in a biodegradable polymer matrix. The 3D silver patterning is achieved through multiphoton-assisted photoreduction. This novel approach offers significant potential for advanced applications such as optical tweezers and micro/nano photonics.

Over the past decades, ultrafast laser internal modification has become a widely adopted approach to enable three-dimensional (3D) micromachining of transparent materials into sophisticated structures and devices with the extreme geometrical flexibility. For the industrial-scale applications of complex devices based on hard and brittle materials like glasses and ceramics, direct fabrication by laser 3D printing is still elusive. In this contribution, a high-resolution, high-throughput ultrafast laser 3D printing method for industrial-scale micro-reactors in glass is developed, through the extreme spatial-temporal manipulation of laser-material interactions deep inside the transparent material. The fabricated glass micro-reactors with sophisticated 3D microfluidic channels and large liquid holding volume usher a revolution in flow-chemistry applications.

Glass is essential in modern applications due to its exceptional properties, yet its additive manufacturing, especially for complex geometries, faces challenges in precise transparency control. We developed an additive-free, photoexcitation-induced multi-transparency glass 3D printing method using polymetric silsesquioxane (PSQ) and direct laser writing (DLW) with two-photon polymerization (TPP). By adjusting laser power, scanning speed, structure thickness, and heating rates during 3D printing, we controlled the transparency of the glass. Raman spectroscopy was used to analyze the polymerization degree and its impact on transparency. Our method allows for precise multi-transparency glass components, enhancing applications and reliability, and addressing stray light suppression in micro-optical systems, thus improving imaging system performance.

We present a platform for manufacturing tuneable and switchable optical elements with very simple drive electronics. Two-photon polymerization direct laser writing is used to structure the director profile of a polymerizable LC in 3-dimensions to form a blazed grating. As the non-laser written regions of the LC remain electrically switchable, the overall device can be electrically tuned. Here we demonstrate a blazed grating that can be electrically tuned to selectively steer an incident beam into 3 different orders with a high (>70%) diffraction efficiency. We further demonstrate its tunability over the wavelength range 490nm to 780nm. Finally, we discuss the scalability of these devices for both extended and additional functionality.