This PDF file contains the front matter associated with SPIE Proceedings Volume 10909, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Industrial High-precision 3D Printing via two-photon absorption (TPA) as a potential disruptive tool for microfabrication enables novel products for diverse applications in the field of optics, photonics, biomedicine, and life sciences. Especially the freedom in design provides one-step fabrication of structures that are not feasible with conventional fabrication techniques or need combined technologies with a required changeover of the workpiece. Up to now, 2PP-fabrication has only been used in the community for structures on the micro and mesoscale due to limited travelling ranges of the translation stages and the field-of-view (FoV) of microscope objectives in combination with galvoscanners to deflect the laser instead of moving the sample relative to the focus. Macroscale elements can be realized via stitching strategies but, however, often induce obvious joints that hinder aimed applications. For this purpose, different fabrication strategies for large scale elements are revealed in this contribution without relying on stitching. Modular machine configurations like inverted focusing through a bath of photoresist (LithoBath3D) enable objects several millimeters in size with micrometer resolution. Additionally, 3D scanning by translation stages only can be efficiently used for the fabrication of large scale DOE structures. For optical elements with high surface quality, precise fabrication is required. As galvoscanners enable high throughput at several 100 mm/s scan speed, TPA-fabricated microlenses are limited to the FoV of the corresponding microscope objective, typically less than 0.5 mm. This limit can be overcome by sophisticated exposure strategies like a synchronized movement of translation stages and galvoscanner (infinite FoV) in combination with advanced beam steering.

A spherical diffraction limited voxel is highly desirable in multiphoton polymerization (MPP) technology, especially for photonic applications. However, currently an elliptic shape voxel having 1:3 or larger aspect ratio is typical in MPP. In order to improve this ratio the more advanced focusing techniques are required. Inheriting from the microscopy, we employed two opposing high numerical aperture microscope objectives in order to create 4Pi excitation in the photopolymer. Here, we describe this technique in detail and experimentally demonstrate the voxel axial length reduction by nearly three times down to 150 nm.

Additive manufacturing – specifically 3D laser lithography – is a powerful technology for the fabrication of functional devices on the micro- and nanoscale. This technique has already been applied in a broad range of fields, including metamaterials, biomedicine, and others. While significant progress has being made in chemically tailored photoresist systems for additive manufacturing, the design of photoresists for subtractive manufacturing on the microscale is still in its infancy. Existing resists for 3D laser lithography can only be removed under harsh conditions, such as calcination, oxygen-plasma etching, or etching with hydrofluoric acid. Herein, we present a new class of on-demand cleavable photoresists for 3D laser lithography. Multifunctional monomers containing disulfide, thioether or silane moieties, which can be specifically cleavage in the presence of a reducing agent or a mild base, are employed. Particularly, dithiothreitol (DTT) causes a thiol–disulfide exchange, erasing the written structure in the first case and sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3) and a fluorine salt (KF) have been proved to sequentially degrade slightly chemically different silane-based microsctructures in the latter case. Thus, these photoresists can be cleaved selectively, which enables the sequential degradation of laser written structures and thereby allows for subtractive manufacturing at the micro- and nanoscale.

Direct metal laser sintering (DMLS) is an emerging additive manufacturing technology that has great potential to change the way parts are manufactured. DMLS is ideal when trying to achieve complex geometries, lightweight metal parts, or reduced components. This presentation compares flawed versus optimized geometry, discusses part design considerations, and explores secondary operation options to keep in mind when designing for DMLS.

Part quality and building time during selective laser melting strongly correlates with the quality of the melting tracks and the melting rate respectively. Conventional processes can be improved by changing their parameters. Increase of the building rate is achieved by modifying the laser beam properties, e.g. spot size and laser power, and process parameters, such as layer thickness and scanning speed. However, process acceleration often leads to appearance of balling, spatters, evaporation and undercuts with subsequent degradation of component quality. The present investigation introduces an innovative way towards increasing of melting rate without lowering part quality. In our approach, the laser beam energy is efficiently distributed on the powder bed by means of beam splitting. This leads to the generation of high volume melt pools. Finally, an outlook on further increase of the melting rate is given.

Printing functional, metal parts for mass production using powder bed fusion additive manufacturing requires the ability to deposit more energy at the working plane to increase build rate. Conventional approaches serially add fiber lasers and scanners to create dual and quad laser machines, but scaling this strategy is limited by the size of powder bed while current scan parameters do not utilize the full output potential of available laser sources. Instead, a processing head containing an array of lower power laser sources can melt wider regions of a powder bed simultaneously to increase build rate. A 16 channel processing head comprised of fiber-coupled direct diodes capable of outputting up to 960W of combined power is presented. Fiber arrays arranged to melt widened tracks of CoCr powder demonstrated builds with >99% density at 2x the build rate of conventional, single laser systems. Details of the array layout, optical system and controls are presented along with scan strategies for melt tracks of varying widths. Most importantly, the array configuration can be scaled to multi-kW outputs spread over larger areas without requiring new parameter development as the energy per unit area remains unchanged with channel count.

With the introduction of Additive Manufacturing, many industrial sectors benefit from the freedom of design and capabilities of this technology. Components can be individually designed and extended with different functions. However, high effort in the post-processing is necessary, since surfaces have to be processed and support structures have to be removed. This post-processing usually takes place outside the Additive Manufacturing machine. Therefore an additional effort is necessary for the machining process, but also for pre- and post-processing of the components. For example, positioning in a CNC milling machine has to be done. It is not feasible to fabricate complete systems consisting of multiple components in a single manufacturing operation. Especially optical systems require high surface qualities. The surfaces usually have to be milled or polished. In order to install the optical system afterwards, an enormous adjustment and assembly effort is needed. This can be bypassed, when both optics and mechanics are manufactured during the same process. However, integrating subtractive post-processing should be avoided as it may cause contaminants that cannot be removed from the system. Transformative processes like laser polishing do barely cause contaminants and are more suited for parallel processing. In this work the integration of a laser polishing system is evaluated, which can be used to reduce surface roughness. The requirements for the light source, manufacturing accuracy, etc. are clarified and concepts, how the integration can be implemented are developed. In addition, possibilities for processing additional materials to manufacture optical systems in one machine are discussed.

Laser Powder Beam Fusion (LPBF)processes use laser beams to selectively melt powder layers and build three dimensional parts layer by layer. Usually, the beam has a Gaussian profile and the melt temperature peaks near the beam center. For typical conditions this temperature is well over the boiling point and drives intensive evaporation. Evaporation-driven recoil momentum can produce detrimental material spattering and keyhole porosity. Evaporation itself consumes a significant amount of energy thus degrading the process efficiency. It can therefore be beneficial to alter the beam shape so as to have the temperature distribution in the melt pool close to that of a flat top. We determined with a simple thermal model the beam shape providing a relatively flat temperature distribution . The optimal is found to be doughnut mode-like, skewed in the scan direction. We did high fidelity simulations of the melt pool produced by the optimized beam and evaluated the possible benefits, including the efficiency increase. We started the experiments with doughnut shape beam far from the optimal but also far from the Gaussian one. The experimental data will be compared with simulation results. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Today, high performance components rely on a controlled heat dissipation by copper layers, which can be applied by laser cladding with lasers in the near-infrared (NIR) wavelength. However, current cladding processes are restricted to copper alloys with reduced heat conduction in order to achieve a sufficient melting of the material. The challenge of pure copper is the high reflectivity in the NIR wavelength range and the variation of the heat dissipation during the melting of the copper material. This leads conventionally to an undefined energy coupling into the substrate and process instabilities, which can cause a variation in the melting depth and pores in the layers. With the application of a laser wavelength of 450nm, the laser absorption in pure copper is highly improved and similar to alloyed copper or even steel, which allows for a reproducible melting even of pure copper material. This processing opportunity is enabled for the first time with the development of a novel high power blue laser source with 1kW output power at 450 nm wavelength in continuous wave mode, which is applied for the cladding of pure copper powder. In this contribution we will demonstrate the performance of a high power blue laser cladding process of pure copper powder on steel and on copper substrate. The assessment of the resulting homogeneity and reproducibility of the resulting copper coatings give new perspectives for conventional applications such as heat pipes or heat dissipation layers but also for new applications such as pure copper components produced by additive manufacturing.

Here we present laser aided additive manufacturing of pure copper parts using ultrashort laser pulses. The process is based on the powder bed fusion of pure copper powder with grain sizes in the range of 5 μm – 15 μm. For processing, a fiber laser system delivering 500 fs pulses at a wavelengths of 515 nm was used. Robust 3D printed parts are generated featuring a high degree of resolution. The fabricated copper samples were characterized in terms of morphology, density distribution, thermal and electrical conductivity. The inner structure is revealed by x-ray computed tomography measurements.

The feasibility of a novel powder synthesis route that is used in laser additive manufacturing (LAM) of oxide dispersion strengthened steels is demonstrated in this study [1]. The route consists of laser processing of colloids [2] and subsequent electrophoretic deposition [3] and leads to powder composites, which are characterized by a homogenous distribution of oxide nanoparticles on the surface of micrometer-sized stainless steel particles. The powder composites are successfully processed by the two LAM processes of LMD and SLM, leading to bulk specimens with low porosities and homogenous distribution of nanoscale dispersoids. Compression tests at elevated temperatures demonstrate the superior performance of reinforced material compared to raw stainless steel specimens. References: [1] C. Doñate-Buendía, F. Frömel, M. B. Wilms, R. Streubel, J. Tenkamp, T. Hupfeld, M. Nachev, E. Gökce, A. Weisheit, S. Barcikowski, F. Walther, J. H. Schleifenbaum, B. Gökce, Materials & Design 154, 360 (2018). [2] D. Zhang, B. Gökce and S. Barcikowski, Chem. Rev., 117, 3990, (2017). [3] R. Streubel, M. B. Wilms, C. Doñate-Buendía, A. Weisheit, S. Barcikowski, J. H. Schleifenbaum, B. Gökce Jpn. Journal of Applied Physics 57, 040310 (2018).

Laser based additive manufacturing is a key technology for sustainable mobility and power engineering. It has undergone a dynamic development in recent years regarding process stabilization, reliability and standardization. However, in the current state laser based additive manufacturing still requires extensive R and D work in process understanding and investigation of material properties as well as developing new materials and advance the process possibilities. To overcome restrictions of commercially available AM machines with regard to necessary powder quantity and adaptable equipment such as sensors and e.g. heating devices two individual laser process chambers (LPCs), manual and partly automated, have been established. In addition to the low powder quantities needed to produce samples for process and material development the LPCs also offer the possibility to manufacture two materials in alternating layers to combine physical properties. A manual LPC is used to produce small scale samples from lab scale adjusted WC-Co powder types to further develop the material class for AM and to deepen understanding of phase formation. WC-12Co with additives is successfully manufactured to a high density and phase formation is investigated. The manual LPC is also used to proof the concept of layered AM structures from a combination of Fe and FeAl for magnetic applications. A further developed and automated version of the manual LPC is then used to produce larger layered samples for further analysis.

Additive Manufacturing (AM) processes as Laser Metal Deposition (LMD) addresses various benefits such as the build-up of complex shaped parts, the possibility of functional integration, reduced lead times or the use of difficult machinable materials compared to conventional manufacturing possibilities. Beside mentioned advantages, the use of more than one material in a component strongly increases the field of applications. Similar to structures in nature, multi-material arrangements can be realized by (I) sharp intersections from one material to the other (e. g. in the case of a thin corrosion protection), (II) graded structures enabling smoother material transitions (e. g. dissimilar materials joined together without defects), (III) composite structures with enclosed particles in a matrix material as well as by (IV) in-situ alloying of different material compositions. Due to varying material properties (e.g. thermo-physical, mechanical, optical), the combination of materials often requires a detailed investigation of occurring process phenomena and well-chosen modifications of the process regimes. Within this paper, (a) the right material feeding as well as powder interaction between various materials in Laser Metal Deposition, (b) the suitable selection of laser wavelengths for different materials, (c) process window adjustments by means of additional sensor equipment, (d) limitations of material combinations as well as (e) results and material characterization of multi-material parts are discussed. Phenomena are discussed by means of exemplary industrial applications, e.g. from the jet engine or medical business.

Wire-based additive manufacturing (WBAM) has been a promising alternative compared to the more established metal printing technologies such as powder bed fusion or laser powder deposition, especially in the large structure buildup, due to the benefits such as high deposition rate, low cost of material, and high material usage efficiency. Wire-based additive manufacturing can be categorized by heat sources: electron beam, laser, arc, etc. Here we will mainly study laser hot-wire direct metal deposition (LHW-DMD) to build a part used in the space industry. Also, Gas metal arc welding (GMAW) and hybrid laser GMAW (HLGMAW) will be explored. In comparison of the three different fabrication technologies, advantages and disadvantages will discussed.

Laser additive manufacturing with metals is gaining more and more attention, and represents a large market in industrial applications, specifically for the aerospace sector in the future. The increasing diversity of applications requires the continuous development of specific process implementations: For high metal deposition rates, developments have focused on arc technologies (Wire Arc Additive Manufacturing, WAAM), based on conventional welding techniques. For high definition 3D parts, the development of laser technologies allowed the implementation of layer-based metal solidification on powder beds known as Selective Laser Melting (SLM). These two processes have specific characteristics, such as high deposition rate with low accuracy for WAAM and low deposition rate with high accuracy for SLM. In this paper, we will present the interest of wire-based deposition technologies with lasers, often referred to as laser metals deposition by wire (LMD-W). This new approach presents the best compromise between high deposition rates and good accuracy which corresponds to the need of the aerospace industry to build “cubic meter sized” parts. It meets the requests in terms of mechanical resistance and process duration. The first tests of the present study are carried out on aluminum alloy. The results show a good aptitude of aluminum despite of a recognized difficulty to implement this alloy in additive manufacturing due to problems with process stability at the edge of the deposit, filling strategies, and many more. In the present paper we focus our developments on the deposition rate in order to realize large aeronautics components.

316L stainless steel plate was fabricated by spatter free selective laser melting (SLM). 316L stainless steel has excellent properties such as corrosion resistance and hardness. But it is difficult to form into complicated structures because of hard to work material. SLM can fabricate complicated shapes because it builds a 3D material layer-by-layer from a powder. Some issues, however, have yet to be resolved, including dimensional accuracy, surface finishes, processing time, and mechanical properties such as surface roughness and hardness. There is some problems that spatter is generated by metal powder scattering on when the laser is irradiated to the powder. Due to the spatter, the input energy to the powder bed becomes insufficient because the laser is absorbed the spatter particle. Therefore it is required the technology to suppress the amount of spatter for SLM process. In this study, in order to clarify the mechanism of the spatter free process, the 316L stainless steel was fabricated by SLM and observed the behavior of powder during the laser irradiation by high speed video camera. As the results, it was revealed that the amount of spatter was depended on the input energy of laser. At the laser fluence of 20 kJ/cm² , the amount of spatter was minimized, and surface roughness on the fabricated sample was improved to 3.5 μm from 30μm.

Additive manufacturing applications, in areas such as aerospace and medicine, are limited due to the lack of process stability and quality management. In particular, geometrical inaccuracies and the presence of mechanical defects hinder repeatability of the process¹. A great disadvantage of AM is that verifying the quality of AM produced parts are mainly done after part fabrication which does not allow the operator to act upon defects observed during the actual build. To break into industries with very high quality standards, an important issue to be addressed is in-situ quality control during a build^{2, 3}. If defects on a new powder layer can be detected before laser melting occurs, a new layer may be suitably recoated or the process can be paused for user controlled rectification. The work which will be presented here is focused on image based process monitoring of a powder bed additive manufacturing system using a shadow casting method. As a proof of principle, a few main defects during recoating will be identified and analyzed to establish the severity and possible impact of the defects on metal powder consolidation. Preliminary results of defects identified before and after material consolidation will be shown. For this, a software package is in development to automatically detect defects. This is aimed towards developing a system which in the future will contribute to quality assurance.

Advances in printed electronics have allowed for the proliferation of rapid prototyping systems in many labs and corporations across the world. These technologies allow for on-demand electronics manufacturing in low volume situations with turnaround times less than 1/5th of conventional electronics fabrication. Additionally, new processes and structures can be tested without requiring retooling, allowing for cheaper process experimentation. Various places in a conventional electronics workflow where these capabilities can be integrated to great effect will be proposed, including model verification, prototype production and special material integration. Furthermore, the possibility of moving towards a software style “agile” workflow for hardware devices will be examined, with the goal of providing a framework for integrating printed electronics techniques in electronics fabrication.

Additive Manufacturing (AM) of low-profile 2.5D glass structures is demonstrated using a fiber-fed laser-heated process. In this process, glass single mode optical fibers with diameters 90-125 μm are fed into the intersection of a workpiece and CO₂ laser beam. The workpiece is positioned by a four-axis CNC stage. Issues unique to the process are discussed, including the thermal breakdown of the glass and index inhomogeneity. Scanning electron microscopy reveals that the core/cladding structure of the fiber remains intact during printing and can be used to guide light for photonic applications.

The use of cellulose as a platform for flexible electronics has appeared as an interesting approach for the development of new technologies, given its unique properties. Usually, printed paper-based electronics have been carried out by standard printing methods such as, for example, screen and inkjet printing. However, since some materials of interest are insoluble, the use of such approaches is limited to soluble materials. This is the case of poly(p-phenylene vinylene) (PPV), a material that presents attractive electrical, photo-luminescent and electro-luminescent properties. In this work we demonstrate the use of femtosecond laser induced forward transfer to produce high-resolution patterns of the conductive polymer PPV onto bacterial cellulose substrate, aiming at obtaining a new approach for the development of cellulose-based structure for flexible electronics. With such approach one were able to transfer PPV, with line resolution of about 10 µm and without materials degradation. Furthermore, to increase the electrical conductivity the samples were subsequently doped being then exploited in the fabrication of functional devices. These results open new avenues in the fabrication of paper-based devices, by combining high resolution and new classes of patterning materials.

Multiphoton absorption polymerization (MAP) is a consolidated technique which allows the fabrication of three-dimensional devices, with high resolution, specific functionalities and nanometric features. In general, to fabricate these devices, different methodologies have been employed, frequently based on complex and expensive experiments. However, no formal investigation has been performed to evaluate how the sample composition can influence the final structure size, without compromising the integrity of fabricated device. Therefore, in this work, using a simple approach, we investigate if the relative proportion of the sample constituents used in MAP can affect the final structure features. Here, we used two three-acrylate monomers, tris(2-hydroxyethyl)isocyanurate triacrylate and ethoxylated(6) trimethylolpropane triacrylate, combined in different proportions with an acylphosphine oxide photoinitiator, known as ethyl-2,4,6-trimethylbenzoylphenylphosphinate. The first monomer provides mechanical stability for the structure and the other reduces the degree of shrinkage upon polymerization. Polymeric structures are fabricated using a Ti:sapphire mode-locked laser oscillator, centered at 780 nm. The laser beam is focused into the sample through a microscope objective (NA=0.85). A pair of galvanometric mirrors and a translational stage allow the laser scanning in all the resin volume, producing three-dimensional structures. Using these acrylate monomers in equal proportion and a typical photoinitiator concentration (3 wt%), we produce structures with feature size on the order of 850 nm. When we change these monomer proportions and increase the photoinitiator concentration, we are able to produce structures at least 30% smaller. This simple approach here demonstrated can be combined with other methods, allowing the device fabrication with nanometric features.

3D laser lithography is a powerful technology to manufacture free-form micro- and nano-optical components. However, practical applications of these components are limited due to lack of knowledge of their optical resilience to intense femtosecond laser radiation, especially in the case of complex-shaped 3D structures. In this report, 3D woodpile structures were fabricated using 3D laser lithography in order to evaluate their laser-induced damage threshold (LIDT). For that S-on-1 testing method was performed on fabricated polymeric nanolatices showing their resilience to femtosecond radiation in the fluence range from tens to hundreds mJ/cm². Furthermore, numerical modeling and experimental investigation were employed to deduce if the chosen geometry provided any photonic properties that could yield a change in the LIDT.

we use a nanosecond laser pulses to create shock waves on material surface. using those shock waves, we are able to generate any three dimensional template with high fidelity. Currently, we use this technique to create shape memory effect on shape memory alloys and other materials. This is a fast environmental friendly and low cost technique.

Due to its flexibility, laser can be used for a wide variety of applications. Applications that are suitable for laser material processing include polishing, hardening, cleaning structuring, soldering and 3D printing (SLM). However, treating of complex freeform surfaces is challenging in terms of track planning. As manual track planning is not economically viable, there is a demand for software solutions for track planning with respect to time-based processes. This paper deals with the development of a software solution for automated track planning with respect to time-based processes. In addition, the introduced software includes postprocessors for fully automated G-Code, Rapid and Kuka Robot Language (KRL) generation. To demonstrate the feasibility and advantage of a time-based offline track planning of robot guided laser application, an additively manufactured freeform surface was laser polished. An application example represents the robot guided laser polishing of a complex 3D freeform surface. Investigations revealed a relative roughness reduction ~92 % of X2CrNiMo17-12-2 steel (1.4404).

Laser scanners have emerged as powerful instrument for high-precision 3D geometry measurement and high-resolution reverse engineering in combination with 3D printers etc. However, such attractive laser scanners have failed to address to fading phenomenon, which was a critical issue of laser scanning systems. Although extensive research has been carried out on the fading issue, no single study exists which effectively coped with such an impairment inherent in 3D geometry measurement using laser scanners. In this article, we propose a 3D laser scanner having a tunable high-speed polarization scrambling scheme and cope with the fading phenomenon. To our knowledge, this is the first report of versatile removal of the fading phenomenon inherent in laser scanning systems

In order to clarify the influence of light absorption characteristics and thermal conductivity of the substrate in forming a pure copper layer using multi-laser cladding system, a pure copper layer was formed on two type substrates. Two lasers were combined at a focal point to set a spot diameter of 507 μm. At the same time, pure copper powder having an average particle size of 34 μm was supplied from a center nozzle. The powder melted and solidified to form a pure copper layer on the substrate surface. The copper coated samples were cut with a micro-cutter, and cross section was observed with the microscope to investigate layer thickness, penetration depth and material organization. As a result, it was confirmed that the copper layer became larger as the laser input energy increased. And compared with the substrates of stainless steel and copper alloy, it was found that the input energy of copper alloy substrate required about 3 times more energy than that of stainless steel substrate. Therefore, it was revealed that the laser input energy depended on the thermal conductivity of the substrate.

Selective laser melting (SLM), a recently developed additive manufacturing method, is capable of directly fabricating three dimensional models from a CAD data, which a laser beam is irradiated on the powder to melt and solidify on a powder bed. In SLM, although a fiber laser with the wavelength of near infrared ray (IR) is employed, it is difficult for pure copper to fabricate a complex shape because of its low light absorption rate to copper. Therefore, we have developed an SLM system using a blue diode laser with absorption rate about 6 times that of IR laser and demonstrated for it possible to fabricate pure copper. In this study, we fabricated pure copper by using the developed blue semiconductor laser of 450 nm wavelength and near infrared semiconductor laser of 915 nm wavelength, respectively, and the effect of laser wavelength in SLM was clarified. Furthermore, in order to optimize the densification of the pure copper material of the sample fabricated by the SLM system, the input energy such as the laser scanning speed and the hatching distance were varied. As a result, the correlation between the energy density of the laser and the relative density of the prepared sample was clarified.

We demonstrate a new precise TOF detection-based surface profilometry technique by utilizing FLOM-PD’s sub-fs resolution electro-optic sampling between an optical pulse train and a microwave signal. The imaging can be realized by scanning the sample’s position laterally, as a scanning LIDAR system does. Using this technique, three samples of different step heights are successfully imaged. Our method achieves high precision of 4.2 nm repeatability and large maximum detectable range of 9.1 mm NAR, and accordingly, dynamic range is larger than 120 dB.