We used laser ablation to fabricate a sub-wavelength structure anti-reflection coating (SWS-ARC) on a 5-cm-diameter alumina lens. With a design aspect ratio height/pitch of 2.5, the SWS-ARC gives a calculated average reflectance of 1.3% between 110 and 290 GHz. Sub-wavelength structure shape measurements conducted on both sides of the lens give 303 mu m pitch and total height between 750 and 790 mu m, matching or exceeding the aspect ratio design values. Millimeter-wave transmittance measurements in a band between 140 and 260 GHz show the increase in transmittance expected with the anti-reflection coating when compared with finite element analysis electromagnetic simulations. To our knowledge, this is the first demonstration of SWS-ARC on an alumina lens, opening the path for implementing the technique for larger diameter lenses.

Global issues such as climate change, environmental pollution, and conservation of resources require manufacturers of internal combustion engines (ICE) to achieve substantially reduced emissions of greenhouse gases and pollutants as well as increased engine efficiency and durability. Condition monitoring and predictive maintenance approaches for sliding bearings in ICEs are key tools for increasing engine durability and saving resources by exploiting more of the useful lifetime of a bearing while avoiding critical engine operation caused by bearing wear and failure. These approaches require appropriate measurement technology capable of acquiring informative parameters that reflect the current condition of the bearings while withstanding the high temperatures and mechanical loads encountered inside the engine and accommodating spatial constraints. This paper deals with research work related to advanced sensor technology that is highly integrated into sliding bearings so that information is obtained nearly directly from relevant areas such as the bearing running layer and the lubrication gap. An isolated, sputtered sensor layer with a thickness of a few micrometers is employed in combination with a laser structuring process to form the desired thin film sensor structure below the bearing running surface. While several measurement parameters and corresponding sensor types are conceivable, this paper focuses on temperature and strain measurements that rely on a change in the electrical resistance of the sensor layer material. Promising sensor layouts and positions targeted for use in condition monitoring applications in ICEs are elaborated in detail. Developments and challenges in implementing the sensor technology concept—in particular with regard to the process of manufacturing the sensor as well as the wire contacting—are outlined in depth. The paper concludes by presenting measurement results obtained with this sensor technology at lab scale as well as an outlook toward implementing the instrumented bearings in ICEs.

To develop a safe and sustainable infrastructure for future missions, In-Space Manufacturing must become state of the art. This paper will propose a novel handling mechanism for powder-based material suitable for the microgravitational environment. Ultrasonic levitation is a promising technology for gravity-independent material handling. The fundamental challenge lies in the trapping of powder-based materials. To assist the material deposition process and stabilize the material handling water is used as a carrier material. A multi-emitter single-axis ultrasonic levitator is employed to levitate PA 12 SLS-powder in a fixed state and initiate a laser melting process to bind the powder material. The spherical levitator uses 72 piezoelectric transducers by Murata, with a levitation radius of 37 mm, which can generate a levitation force of up to 0.15 mN. A 20 W 1064 nm fiber laser is employed to evaporate the water and bind 0.4 mu g PA 12 particles together. The experiments will be performed under earth and atmospheric conditions. This paper investigates the evaporation time of water inside a levitation field depending on the laser power. The properties and parameters of distinguished materials will be evaluated to determine the boundary conditions of the acoustic levitator. The data will be compared to a simplified analytical model and used to initiate a melting process with the SLS material.

A large range of laser-matter applications employ ultrashort pulses and high laser intensity. Such processes can lead to unrequired X-ray generation, which represents a hazardous radiation factor even for common laboratory research-grade laser systems. We present here an analysis of the radiation dose rate and X-ray spectrum emitted during ablation of a rotating copper cylinder with respect to several laser parameters. The results show that focused sub-picosecond pulses with intensity above 1013 W/cm2 can exceed the annual irradiation limit even in one hour, requiring appropriate shielding for the safety of the researchers.

Fabrication technologies for the semiconductor industry have enabled ever smaller electronic components but now face a fundamental limit in their assembly. As the components get smaller and smaller, the difficulty of assembly increases. At the same time, the number of components per circuit board area is growing, as is the case with LED displays. This in turn calls for an increasing assembly rate. The conventional pick-and-place method can handle approximately 25–30 thousand dies per hour but has increasing limitations when component dimensions are reduced below 150 μm edge length. Laser-induced forward transfer is used as a potential alternative for an assembly of semiconductor components. This technique allows to transfer semiconductor components with an edge length of less than 150 μm to a target substrate. The current process is contactless, damage-free, and has sufficient placement accuracy. If this process is combined with the property of high-pulse repetition rates, it is possible to significantly increase the assembly rate of semiconductor components compared to the current limitations. The aim of this study is to characterize the flight properties of silicon semiconductor components of various dimensions in a laser-driven transfer process using optical imaging methods. This method allows to analyze velocity, the direction of fall, and acceleration of falling components. The results can be used to analyze the transfer behavior of various component sizes and to make estimates of the stability of the transfer process.

In micro-material processing with ultrashort laser pulses (USP), the surface quality during drilling and thin film ablation varies with the scanning speed and the pulse repetition rate. However, while high pulse repetition rates tend to be desirable, local heat accumulation caused by increasing pulse overlap is counterproductive. Thus, the scanning speed must be scaled with the pulse repetition rate, preferably by supplementing the already existing setup. In this work, we present a dynamic extension through the combination of an acousto-optical deflector (AOD) with a galvanometer scanner. This combines the best of two worlds: the dynamic beam deflection of the AOD and the large scanning field of the galvanometer scanner. The integrated AOD is able to deflect the laser beam pulse by pulse within its scanning field and to modulate the beam intensity simultaneously. The mechanical limitations and problems of the galvanometer scanner, such as vibrations and overshoots due to fast mirror rotations, can be specifically compensated by the high precision of the AOD. As a result, in addition to process time reduction, the surface and image quality improves significantly. In any case, the laser source needs synchronization with the AOD because the propagation of sound waves within the AOD crystal is slower than the laser pulse propagation through the medium. In the first step, a comparatively slow AOD based on tellurium dioxide with a transversal crystal alignment is used. The process time of a thin film ablation with 4 μJ at 1 MHz was reduced considerably by applying a USP laser system (Coherent Monaco).

Ablation of thin metal films with laser pulses having a pulse duration shorter than the electron-phonon relaxation time, so called ultrashort laser pulses, enables melt-free patterning of arbitrary geometries. Ablation with ultrashort laser pulses is an emerging process and is currently used in the field of microelectronics for the repair of photolithography masks and in the photovoltaic industry for patterning of indium tin oxide (ITO). Another current field of investigation is the patterning of thin film strain sensors. In order to achieve the desired ablation quality, a multipulse irradiation is often required. Currently, there is no “simple” model to predict line and more complex ablation geometries created by multipulse irradiation. Within this paper, an incubation threshold is introduced to enhance an existing incubation model, which is restricted to the prediction of point ablations. The resulting phenomenological model is experimentally verified on thin NiCr films using 10 ps laser pulses. The usability of the derived model is significantly higher than other existing models due to concentrating on the relevant criterion for patterning of electronic circuits: the removal threshold as well as an easy to handle procedure to determine the model parameters, which can be determined on a machining setup in industrial conditions.

Current trends of intelligent products and controlled processes show an increasing need for long-living sensors. Metal thin-film strain gauges are suitable for monitoring mechanical loads over the entire lifetime of a component. However, existing manufacturing methods can only pattern these gauges on flat components and in large quantities to ensure an economical process. To overcome these limitations, a patterning process based on ablation using picosecond laser pulses has been developed and is the subject of this paper. Starting with the analysis of the ablation behavior of the sensing and insulation film, a process window is derived. The sensing properties and the achievable reproducibility are characterized and a trimming process to improve the reproducibility of the patterning process is developed. The pattering process developed is an important prerequisite for the integration of thin-film strain sensors on 3-D surfaces for products such as bearings, or in products which are typically manufactured in small quantities, such as medical implants.

This paper concentrates on the characterisation of the ablation process of thin strain sensitive NiCr films deposited on Al2O3 substrates. The optical skin depth of NiCr (80/20) is identified. Removal experiments with single and multiple pulse point ablations are carried out on Al2O3 bulk substrates with different NiCr thicknesses. The experiments reveal the maximum NiCr film thickness for single pulse ablation. NiCr films with a higher thickness have to be processed in a multiple pulse processing strategy. Calculation of the beam radii using Liu plots revealed radii larger than the actual measured beam radius. The radius increase has been identified to consist of two parameters, one representing a special jitter of the experimental setup used, and a second thickness dependent parameter.

High-resolution laser patterning offers innovative methods for the manufacturing of three-dimensional interconnect devices. The process chain presented in this paper uses cost efficient metal thin-films sputtered on thermoplastic sheets and two-dimensional high speed laser-processing, whereas the three-dimensional shape of the end product is realized by deep drawing of the machined sheet. Due to the lower fracture strain of metals in comparison to thermoplastics extensive fragmentation of the deposited metal film occurs during deep drawing; therefore picosecond laser fine structuring is used to provide strain relief in the circuitry and to preserve the conductivity after the drawing process.

Radial and azimuthal polarizations have attracted new interest in the process development community due to improved beam propagation and absorption conditions in the ablation cavity. This paper presents our recent activities and results on polarization converted ultrashort laser pulses by use of segmented half-wave-plates for the generation of ripple structures with predetermined sub-patterns. The formation of ripples fabricated in metals, ceramics, and semiconductors is analyzed by the morphological investigation of the structures (spacing and orientation) as a function of the polarization state of the laser beam.