This PDF file contains the front matter associated with SPIE Proceedings Volume 11271 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

The use of two-photon absorption (TPA) for polymerization, also known as 3D Lithography, Direct Laser Writing, or High-Precision 3D Printing is gaining increasing attraction in industrial fabrication of micro- and nanostructures. Mainly due to its vast freedom in design and high-resolution capabilities, TPA enables the fabrication of designs which are not feasible or far too complicated to be achieved with conventional fabrication methods. TPA is a scanning technology and fabrication in 3D requires axial overwritings. High industrial throughput fabrication can be achieved by intelligent fabrication strategies combined with an excellent material basis. Further boosting the throughput can be achieved by multispot exposure strategies. In this paper, massive parallelization is demonstrated which was realized by using a beam splitting diffractive optical element (DOE). Simultaneous fabrication using commercially available acrylate-based hybrid resin with 121 parallel focal spots arranged as 11 x 11 array is reported. Structures fabricated by a single laser beam and by 121 parallel beams are compared to each other with regard to shape and polymerization threshold. It was found that polymerization is strongly increased when parallel beams are used, especially for the central beams. As a result, polymerization threshold is lower in the center of the 11 x 11 array compared to the edges of the array. Furthermore, structures at the center of the 11 x 11 array are bigger compared to structures at the edges of the array when assigning equal intensity to all diffracted beams. These results are attributed to diffusion of photo initiators, quenchers, and radicals.

In this work, two optical microfabrication methods are combined in a single system to enable automated fabrication of ordered three-dimensional microgranular crystals. The holographic optical tweezers approach offers precise and simultaneous handling of numerous microparticles, while two-photon polymerization enables selective joining of microparticles in desired crystal arrangements. Microgranular crystals exhibit unique nonlinear dynamic behaviors and have applications such as photonic crystals, acoustic lenses, and in shock absorbing materials. This novel fabrication approach holds potential to enable the next generation of hierarchical architectured metamaterials that cannot be fabricated with existing techniques.

We are presenting a model for a quantitative description of the polymerization process in 3D-laser microfabrication. With aim to assist in estimating the necessary power threshold to obtain certain feature size, particularly the line characteristics, depending on the laser power and writing speed. The focal distribution as well as the photoresist is taken into account. We do not try to gain any chemical insight into the processes involved, and restrict us to a quantitative study of a multi-photon process. Machine learning is used to classify the input SEM images providing a look-up table as a custom field for optimized parameter selection.

Laser Induced Forward Transfer (LIFT) is a digital, non-contact printing technology of solid metals as well as viscous inks and pastes. It is highly promising for various printed electronics applications, also when high-resolution is required given its versatility in printable materials, controlled droplet volume down to <100 fL and accurate positioning down to <~5μm. Moreover, since typically no post-processing is required, deposition on a wide range of sensitive substrates is made possible. We will demonstrate high speed and high-resolution LIFT printing of electrical circuitry relying on fast material supply in the form of metal coated foil and fast, random access, laser beam steering. Examples of printed porous material structures will be shown as a demonstration to the capacity to design and fabricate materials with specific thermal, electrical and mechanical properties.

2D materials such as graphene have great potential as the basis for novel optoelectronic devices. Typically, 2D materials are produced via chemical vapor deposition and therefore form continuous layers. Here Laser Induced Backwards Transfer (LIBT) is used to deposit pixels of 2D materials with precisely controlled size, shape and position. In LIBT, part of the laser energy that is absorbed in the donor substrate becomes kinetic energy imparted to the 2D material, causing localised transfer of 2D material onto the receiver. The capability to deposit high-quality intact 2D materials, in well-defined microscale pixels will eliminate costly and time-consuming lithographic processing.

Many companies are new to additive manufacturing and want to take advantage of the benefits provided by metal 3D printing (lightweighting, component reduction, internal channels) in end-use applications. Oftentimes these applications have high-requirements and call for process validation, material traceability, inspection reporting, tracing heat treat cycles, specific quality certifications, and several other post-build processes. This presentation will help attendees understand how parts are built using direct metal laser sintering, how to design for the process, and the additional resources required for process validation, material traceability, and quality inspections. Whether the attendee is new to additive manufacturing or evaluating metal 3D printing technology for their production project, this presentation will help identify when the technology provides the most value and what to consider when used to manufacture highrequirement parts.

A 500°C preheating system is used in multi-laser fusion processes to overcome defect formation, and to successfully manufacture highly dense, crack-free, low distortion parts from 1.2343 hot working steel and aerospace grade Ti6Al4V ELI. With a three-laser opto-mechanical focusing and scanning system, we demonstrate high precision laser metal fusion over 300mm diameter fullfield overlapping scan fields at high productivity. Results of density, surface quality and material properties are presented. Control of oxygen level in parts and powder is demonstrated over multiple powder reuse cycles.

This paper describes the development of suitable process parameters to ensure a reproducible, defect-free production of pure copper specimen via Laser Powder Bed Fusion (LPBF) also called Selective Laser Melting (SLM). Therefore, a set of experiments was developed and evaluated in a Design of Experiment (DoE) which finally provide an indication about ideal process parameters for melting pure copper powder at a wavelength of 1064 nm. For the experiments Cu-ETP with a copper purity of more than 99.90 % was processed with a laser power of up to 500 W resulting in a maximum density of 99.82 % and an electrical conductivity of 56.88 MS/m. Besides the development of optimal parameter combinations of laser power, laser speed and hatching distance, focusing the laser beam to a spot diameter of about 35 μm with a fused silica f-theta lens and thus high energy intensities of about 416 kW/mm² resulted in best materials properties.

We present recent advances of pure copper, copper alloy and precious metal additive manufacturing with green, frequency doubled disk lasers achieved by the exploration of process parameters to specifically address the unique laser processing challenges of this class of high reflective, high conductive materials. Results are presented for the analysis of samples made from pure copper, and from the CuCr1Zr alloy. The material properties density, electrical conductivity, and sample properties as geometrical resolution and surface roughness are presented. Part performance in application is discussed.

Laser powder bed fusion processes are driven by scanned, focused laser beams. Along with selectively melting the metal powder, laser energy may be converted and transferred through physical mechanisms such as reflection from the metal surface, heat absorption into the substrate, vaporization, spatter, ejection of heated particles, and heating of the metal vapor/condensate plume that is generated by the laser-metal interaction. Reliable data on energy transfer can provide input for process modeling, as well as help to validate computational models. Additionally, some related process signatures can serve better process monitoring and optimization. Previous studies have shown that the proportion of the transfer mechanisms depend on laser power, spot size, and scan speed. In the current investigation, the energy conservation principle was used to validate our measurement of reflected energy, absorbed energy, and energy transfer by vaporization on bare plates of Nickel Alloy 625 (IN625). Reflected energy was measured using an optical integrating hemisphere, and heat absorbed into the substrate was measured by calorimetry. Transfer from vaporized mass loss was measured with a precision balance and used to establish an upper bound on energy transfer by mass transfer. In addition to measurement of total reflected energy, the reflected laser power was time-resolved at 50 kHz in the integrating hemisphere, which provided insight into the process dynamics of conduction, transition, and keyhole modes.

Laser assisted powder bed fusion of pure Aluminum and hypereutectic Al-Si using ultra-short laser pulses at different pulse lengths is presented. The experiments were carried out with a fiber laser system delivering pulses from 500 fs to 600 ps at a wavelength of 1030 nm and a repetition rate of 20 MHz. Time dependent reflectance measurements indicate that the absorption is increased towards shorter pulse durations. In comparison to longer pulses and cw radiation, powder bed fusion using ultra-short laser pulses lead to uniform structures at lower average powers yielding a homogeneous microstructure that exhibits optimized mechanical properties.

Current manufacturing techniques are limited in their ability to fabricate 3D multiscale multi-material structures. Few research groups have utilized the ability of ultrafast lasers to shape hydrogel materials into complex 3D structures. However, current laser based methods are limited by scalability, types of materials, and incompatible laser and materials processing requirements, thereby preventing its widespread use. In this work, we report the design and development of a Hybrid Laser Printing (HLP) technology, that combines the key advantages of additive stereolithography (quick on-demand continuous fabrication) and multiphoton polymerization/ablation processes (high-resolution and superior design flexibility). Using a series of proof-of-principle experiments, we show that HLP is capable of printing 3D multiscale multi-material structures using model biocompatible hydrogel materials that are highly difficult and/or extremely time consuming to fabricate using curruent technologies.

Nowadays the laser is a conventional tool in industrial manufacturing, for a wide spam of applications, from subtractive to additive, from cutting to welding. The main topic in production today is headlined with the word digitalization and Industry 4.0. In this context the laser is playing a dominant role, because it is possible to produce a part directly from a digital model by contactless processing. This unique feature allows for monitoring processes with smart devices, which is a key issue of Industry 4.0. Especially sensor technology is a leading part related to Smart Factory and predictive maintenance and even process control. Transforming machine elements into intelligent cyber physical systems involves the integration of smart sensors for condition and process monitoring. This contribution of Precitec to the SPIE LASE Conference will present some of the highlights in the area of laser metal deposition and 3D printing using innovative laser processing heads in combination with sensor strategies to fully monitor and even control the manufacturing process with the OCT sensor principle. Sensors based on OCT (optical coherence tomography)/ low coherence interferometry are different to all the other technologies because the measurement is not affected by the process emissions and thus open new horizons in laser materials processing. The use of this method in laser applications has risen in the last years. Since its first appearance in 2008 [1], application examples were shown for laser cutting [2], selective laser melting [3], laser micro machining [4], laser drilling [5] and laser welding [6]. For the latter, a huge potential is foreseen [7] [8].

A major challenge with productionizing Laser Blown Powder manufacturing processes is developing robust process control methods to verify material quality. Laser deposited structures are sensitive to the underlying substrate, including its chemistry, thermal properties, geometry, surface roughness, appearance, etc. It is therefore challenging in many applications to ensure that the deposited material produced on control samples is representative of that deposited on production hardware. Understanding the influence of the different substrate properties would enable more representative control samples to be designed and the effectiveness of the process control methods improved. A set of experiments were completed to compare the influence of two surface finishes (ground and grit-blasted) and two superalloys (cast single crystal CMSX-3 and annealed Inconel 718) on Laser Blown Powder structures. A single layer was deposited on small sample plates to investigate deposition geometry. In this study, laser power and travel speed are used to vary the heat input while powder feed rate is adjusted according to the travel speed to maintain a constant linear feed rate. This work highlights the role of key variables on the deposition geometry. It was found that the two materials show similar responses, even though they have different compositions and differing thermo-physical properties. In the range investigated the surface texture exhibits the greatest influence with large variation in deposit width and penetration. Surfaces whose appearance had been dulled through grit blasting absorb much more energy than ground surfaces due to a higher disposition for multiple scattering.

In this paper, we report our recent research progresses on the design, fabrication and characterization of photonic sensors for harsh environment applications, with the help of novel Integrated Additive and Subtractive Manufacturing (IASM) system. Glass 3D printing with direct laser melting process in this IASM system presents the dimension accuracy on the order of tens or hundreds of microns. The addition of laser micromachining allows the fabrication of structures with micron dimension accuracy, showing the unique advantage of IASM system in high dimensional accuracy compared with traditional 3D printing process. A number of photonic sensors and devices will be summarized and presented, including (1) 3D printed all-glass fiber-optic pressure sensor for high temperature applications, (2) Information integrated glass module fabricated by IASM and (3) IASM for microfluidic pressure sensor fabrication.

During the last decade, laser assisted additive manufacturing evolved to a serious alternative to traditional manufacturing methods. The greatest benefit lies in the realization of almost any desired geometry impossible to create with common molding or cutting processes. Due to the lack of linear absorption in the visible and near infrared, transparent dielectrics like glass are challenging materials for laser powder bed fusion (LPBF). Here, a comparative study on the additive manufacturing of pure fused silica glass parts is presented. For the fusion process, either a common CO2 laser system working at 10.6 μm or an ultrashort pulse (USP) fiber laser system at 1030 nm were applied. While the mid-infrared laser radiation from CO₂-lasers is absorbed linearly, ultrashort laser pulses benefit from their extremely high peak power leading to strong nonlinear absorption. In contrast to alternative approaches [1], there was no need for binding materials. For both systems, a comprehensive parameter study is presented, highlighting major differences like surface quality, resolution and processing time.

The increasing demand for novel fiber design has brought major challenges with the current fabrication methods. Additive manufacturing is an innovative fabrication process that has been attracting attention to the optical fiber community. 3D printed porous bodies from commercial silica powder were produced based on selective laser sintering (SLS). Complex structures such as antiresonant fiber (ARF), photonic crystal fiber (PCF) and multicore fiber (MCF) preforms were produced by this method. Additionally, a multi-material fiber with a silica cladding and a GeO₂-SiO₂ core was fabricated from a 3D printed preform. The optical and physical properties of the fabricated 3D printed structures were reported.

Laser-based drawing methods for rigid objects need precise alignment and often suffer from limitations with regard to the target posture. We propose a method of drawing for posture-free objects using photochromism. We utilize a camera-laser coaxial optical system, high-speed visual feedback, and active marking to mark dots for tracking onto the target surface while drawing the intended lines. The method enables simple calibration and drawing onto rotationally symmetric and planar objects, and ensures robustness to the object’s slight movements, thus leading to all-around drawing. The evaluation experiment confirmed that the proposed method has high drawing accuracy onto both static and rotating objects, as the drawing errors was within 1 mm on average, and can draw even onto a curved surface of a rotationally symmetric object.

Femtosecond (fs) lasers are well established in material processing. Both additive and subtractive processing can be realized with them. Modern amplified fs laser systems can be heavily tuned allowing to use single light source to realize all relevant processing regimes. In this work we exploit it in order to achieve hybrid additive-subtractive 3D micro- and nanomanufacturing. For fabrication we chose highly promising medical devices such as very precise flow meter cell membrane perforators based on microblades or spinning microneedles. We show that the capability of choosing processing regime and perform everything in one workstation simplifies design and fabrication process.

Freeform and microstructured features are generated by MultiPhoton Polymerization with an ultrafast laser, on tool-steel inserts, for microreplication of optical surfaces. The generation of optical surfaces has been studied by combining laser machining and multiphoton polymerization techniques. Resolution in the range of few microns, down to 300 nm lateral dimension, has been targeted on the optically enhanced surfaces. The microstructured surfaces have been further replicated by injection molding on polymer components of several cm². The fabrication accuracy and precision has been evaluated in terms of lateral and vertical resolution of the laser generated features, and the replicated ones. The technology aims to simplify the assembly routes for heterogeneously integrated optoelectronics through direct overmolding of the optics on the components (transceivers, LEDs or sensors), with drastic improvements in cost, productivity and performance.

We present our latest work into the modelling and laser fabrication of 3D auxetic metamaterials, and their evaluation as scaffolds for cell growth. Auxetic metamaterials are materials that display a negative Poisson’s ratio; when stretched, they become thicker perpendicular to the applied force. Their properties are due to their architecture, rather than their chemical composition. Natural biological tissues display auxetic characteristics in organs such as skin, artery, tendon, and cancellous bone. To make these metamaterials scaffolds, we employ 3D multiphoton polymerisation, using a biocompatible tailor-made zirconium silicate. Finally, we investigate the suitability of these metamaterials as scaffolds for cell growth.

We introduce stimuli-responsive structures fabricated by 3D laser lithography. The key material is a responsive hydrogel. It is based on supramolecular host-guest chemistry, which allows reversible actuation under physiological conditions. Combined with other photoresists, multi-material scaffolds are used to directly study live cell behavior during spatially and temporally well-defined changes in the extracellular surrounding. Digital image correlation enables us to precisely track and analyze the behavior of a multitude of cells in a single experiment. With this versatile technique we will study the mechanoresponse of cells and the role of different proteins in the mechanotransduction.

Interactions between tumor cells and immune cells are sparsely explored in 3D models, although occasional studies with 3D cell culture technologies have confirmed that tumor architecture influences cancer cell-immune system interactions. The development of technologies enabling controlled analysis of tumor-immune system interactions especially in 3D is highly challenging. Two photon polymerization (2PP) as a method for fabrication of various microstructures suitable for preparation of 3D tumor models finds applications in this context. In the present study 2PP technology was used to fabricate polymeric microfibers in 3D microspace that mimic fibers of extracellular matrix. UV-curable polymer OrmoComp (Micro Resist Technology GmbH) was irradiated by Newport Spirit ultrafast amplified laser operating at 520 nm. The fibers were made with one side anchored to the substrate with the supporting structure, whereas the other side was freely movable in space. The shape and curliness of fibers were adjusted by alternating parameters of fabrication, namely energy intensities and speed of fabrication. Before exposing fabricated fibers to live cells, microstructures were processed with KOH based treatment to enhance adhesion of cancer cells. Arrangement of the cancer cells in the network of polymeric fibers was visualized by confocal scanning microscopy. Cancer cells were able to proliferate and form spatial cellular clusters among polymeric fibers after several days of cultivation. At the same time they were available to immune cells that could be supplemented to the culture at any time. The results of the present study document feasibility to use 2PP technology to develop in vitro 3D models suitable for studies of tumor-immune cell interactions.

We developed several blue diode lasers and applied laser metal deposition one of the additive manufacturing technologies. This system has two laser modules, a focusing head, a powder feeder and a XYZ stage. Fiber couple direct diode laser module was guided to focusing head by optical fiber, which core diameter is 400 μm. In case pure copper layer formation with blue diode laser, the laser output power is 80 W, a scanning speed is 10 mm/s. A powder feed rate was varied from 14 to 80 mg/s. The stage was moved to the X direction. And In case pure copper rod formation with blue diode laser, the laser output power is 80 W and a scanning speed is 4 mm/s. A powder feed rate was varied from 14 to 80 mg/s. The stage was moved to the Z direction. Layer thickness was linearly increased to 40ms in all powder feed rate and the layer formation rate was gradually decreased over 40ms. An average slope Δspeed = 4 mm/s at 40 ms is obtained. From this, it is considered that pure copper rod can be formed by pulling upward at 4 mm/s. Based on the results obtained from copper layer, pure copper was stacked upward (direction Z) to form a pure copper wire. The result as expected was obtained by raising the speed at 4 mm/s. And since a thin molten pool was formed only in a limited area, it was observed that the molten pool was piled up without melting. It was confirmed that the flying powder adhered without melting. And thereafter, it was melted to form a rod. It was confirmed that there were no pore in pure copper rod.

Wearable strain sensors are attracting great attention owing to their remarkable applications in physiologicalmonitoring and motion-sensing. However, there are two limitations for the fabrication of wearable strain sensors because additional material synthesis process and additional adhesive material are necessary. In this presentation, we introduce the method for the fabrication of wearable and attachable strain sensors without additional process and material. By controlling laser parameters, we successfully fabricated wearable and attachable sensors consisting of silver nanowires and polymer having diverse mechanical and adhesive properties. Our work helps guide fabricating nanowire-based resistive wearable strain sensors using the laser- based 3D printing.

A multi-beam type laser metal deposition (LMD) system equipped with two blue diode lasers (B-LMD) was developed to form a three-dimensional object production of a pure copper rod. Beams output from the two blue diode lasers are combined at the focal point, and pure copper powder is supplied there, the processing head is moved in the vertical direction to continuously melt and solidify the pure copper. A 100 mm long pure copper rod was formed in 25 seconds with multibeam LMD system using two 100 W-class blue diode lasers. The long side of the formed pure copper rod was 780 μm and the short side was 600 μm, which was larger than the spot at the focal point. Observation with a high-speed video camera showed that the pure copper rod was formed with a thin molten layer at a position 300 µm away from the focal point ( Z = 300 μm). When the laser profile at Z = 300 μm and the cross section of the pure copper rod were overlapped, the size of the pure copper rod coincided with the laser irradiation.