Search

Micro milling is a common process for micro structuring component surfaces, e.g. for manufacturing material measures that are applied for the calibration of areal surface topography measuring instruments. In this study, the surface topography of material measures is investigated using various evaluation approaches (integral approach, correlation analysis, Fourier analysis). In doing so, confocal microscope and atomic force microscope measurements are used to compare cutting parameters for the appropriate micro milling process. For two milling tools it is shown that the surface topography depends primarily on the spindle speed and much less on the feed per tooth whereas differences between the milling tools are observed in the tendency to form substructures.

The trend towards hybrid materials consisting of metals and polymers is strongly driven by requirements such as weight reduction and improved functionality. A crucial step towards new hybrid materials is the advancement of joining technology. While metals and polymers are currently often joined using adhesives, this technology has major drawbacks such as long process cycle time, low robustness with regard to changes of the material composition, and are almost impossible to recycle, a point which is becoming increasingly important. A promising joining method is thermal direct joining of metals and thermoplastic polymers due to its fast cycle time, its robustness of the process and the absence of duroplastic adhesives. Direct joining requires surface treatment of the metallic joining partner prior to the thermal joining process to achieve a sufficiently high contact strength. It is known that laser-induced topologies on the metal surface are beneficial with regard to contact strength of the joints. Designing a joint based on laser structured metals requires a fundamental understanding of the interface interactions. The present paper focuses on the influence of surface enlargement on the joint strength. Laser pretreatment was utilized to generate surface structures with specific surface enlargement on the metallic joining partner. The pretreated metallic parts were subsequently joined with a thermoplastic polymer by injection molding. The joint strength was investigated in single lap shear tests. The key finding is that the contact strength increases almost linearly with the surface area within the tested parameter range, while the structure geometry parameters have only a minor influence. This may help as a design guideline for future adhesive-free hybrid material joining technologies.

To address the significant subsurface damage of a workpiece after grinding by a coarse-grained wheel, the research on nanosecond ultraviolet laser micro-structuring of a coarse-grained diamond-grinding wheel was carried out, and the influence of process parameters on the depth and width of the groove, the micro-structuring efficiency, and the qualification rate of micro-structured grains were explored. The results show that the single-pass laser circular cutting method cannot achieve the desired groove size even with an arbitrarily large number of scanning cycles. The multi-pass laser circular cutting method can effectively improve the micro-structuring efficiency, and the width and depth of the groove increased and decreased respectively with the increase of the pass spacing. The qualification rate of micro-structured grains was related to the groove spacing, the distribution of the grains on the surface of the grinding wheel, the grain diameter, and the groove width. Under the assumption that the grains were evenly distributed on the surface of the grinding wheel, the qualification rate first increased and then decreased with the increase of the groove spacing.

High precision multibeam processing is a useful approach to increase the productivity of high precision laser material processing by means of ultrashort pulsed (USP) laser radiation. In the field of micro- and nanostructuring multibeam ultrashort pulsed laser processing attracts increasing attention due to its ability to generate periodic pattern like filters within an economically reasonable time of up to 12.000 holes/sec. Thus, this technology has become relevant for applications in the filtration industry and biotech industry. The developed multibeamscanner (MBS) is capable of drilling holes with extremely small outlet diameters (< 1μm) into various materials with a customized arrangement and a density of more than 10.000 holes per mm². The aim is to investigate how the exit diameter of single-digit sized holes can be further reduced using the multibeamscanner and whether an increase in productivity is possible.

Textured metallic parts with multiple-scaled micro-structures have significant advantages for anti-counterfeit applications. For this purpose, the development of an automatized micromachining laser-platform is introduced, which is capable of handling different laser based fabrication methods including direct laser writing (DLW) and direct laser interference patterning (DLIP), using only one laser source (Nd:YAG laser, 1064 nm wavelength, 500 ps pulse duration). Using DLW, line, cross-like and rectangular structures with length scales from 50 to 150 µm were produced, while DLIP was used to produce line-like patterns structures, with 3.7 and 25 µm spatial periods. In addition, laser induced periodic surface structures (LIPSS) were also combined and thus obtaining hierarchical patterns with three different length scales in one process. Finally, additional samples were automatically structured to produce examples of definable security features at the touch of a button. The surface topography of the treated samples is analyzed using scanning electron microscopy, optical microscopy and white light interferometry methods.

Laser radiation is used, among others, for surface treatment of various materials. At the Institute of Optoelectronics, under the direction of the late Professor Jan Marczak, a number of works in the field of laser materials processing were performed. Among them special recognition deserves flagship work of Professor Jan Marczak: implementation in Poland laser cleaning method of artworks. Another big project involved the direct method of laser interference lithography. These two projects have already been widely discussed in many national and international scientific conferences. They will also be discussed at SLT2016. In addition to these two projects in the Laboratory of Lasers Applications many other works have been carried out, some of which will be separately presented at the SLT2016 Conference. These included laser decorating of ceramics and glass (three projects completed in cooperation with the Institute of Ceramics and Building Materials), interference structuring medical implants (together with the Warsaw University of Technology), testing the adhesion of thin layers (project implemented together with IFTR PAS), structuring layers of DLC for growing endothelial cells (together with IMMS PAS), engraving glass for microfluidic applications, metal marking, sapphire cutting and finally the production of microsieves for separating of blood cells.

A current challenge in laser processing is high precision micromachining of transparent materials, e.g. to manufacture microoptical elements. This can be achieved amongst others by using laser induced backside wet etching. Research has been done by several groups in the last years. Most of the published results were obtained by using UV excimer lasers. Our approach deals with the implementation of the technique for NIR laser sources. We investigated the effects of different pulse widths and repetition rates on laser induced back side wet etching for 1064 nm wavelength and for different absorbers.

This paper describes the laser micro structuring of forming tools for hot embossing. The laser micro structuring allows the manufacturing of the required structural sizes and structure forms as well as the machining of the applied tool materials which can not be manufactured with conventional processes like milling. Through the systematic investigation of the influences of single laser parameters it is possible to influence the processing of 2-D and 2 1 2 -D micro fluid geometries. For initial experimental investigations the high strength ceramic material silicon carbide is used.

Microstructuring of highly reflective metals was performed using high-power nanosecond- and picosecond-laser beam sources. This contribution mainly focuses on the ablation depth, achievable sidewall inclination angles and the ablation quality. Single- and multilayer structures with varying width and depth were generated to analyse the interdependency of the resulting ablation quality with the processing parameters and strategies used. As results, optimized strategies to generate different geometrical structures with specified qualities and processing times are proposed. In addition, an effect occurring at ps-multilayer ablation, which was up to now only described theoretically, will be presented.

The use of ultrashort laser pulses has been shown to be an attractive option for high quality micromachining. In these applications low energy laser pulses are tightly focused to achieve high light intensities. While this approach has been demonstrated to be successful, its application is challenged by the short Rayleigh range of a tightly focused laser beam. Precise positioning of material samples becomes crucial imposing extra requirements on sample flatness, tilt, and irregularities. To overcome some of these limitations an application of non-diffractive Bessel beams for laser material processing has been attempted recently. The non-diffractive focus of Bessel beams can have the depth of field significantly longer than the Rayleigh range of a Gaussian beam of a comparable diameter. With sub mJ laser pulse energy the light intensity along the line focus can reach and exceed the required threshold levels making laser Bessel beams suitable for material processing. Preliminary numerical simulations show that truncated by a micron size aperture Bessel beam still has the propagation depth sufficiently long to be suitable for volumetric micro structuring of non transparent media. The paper aims to demonstrate feasibility of ultrafast laser structuring of non transparent media using Bessel beam focusing geometry.

Fast parallel femtosecond laser surface micro-structuring is demonstrated using a spatial light modulator (SLM). The Gratings and Lenses algorithm, which is simple and computationally fast, is used to calculate computer generated holograms (CGHs) producing diffractive multiple beams for the parallel processing. The results show that the finite laser bandwidth can significantly alter the intensity distribution of diffracted beams at higher angles resulting in elongated hole shapes. In addition, by synchronisation of applied CGHs and the scanning system, true 3D micro-structures are created on Ti6Al4V.

Femtosecond lasers belong to the most exciting kind of lasers. They are used in science, medicine and industry where their light serves for example as optical probe for time-resolved studies, the analysis of biological material or the micro structuring of advanced material components.

This chapter is focused on laser ablation for micro-structuring. Basic properties of laser ablation are, firstly, introduced, which addresses the principles of the laser interactions with materials, absorption effects on ablation geometry, and thermal effects on ablation precision and geometry. These are followed by presenting process principles and techniques for laser ablation for micro-structuring, such as using mask technique and scribing technique, for which some application examples are given, including micro-structured replication tool for self-assembly and micro-fluidic channels.

Der Werkstoff Glas ist zunehmend ein interessanter Konstruktionswerkstoff fur die Mikrotechnik. Zur Mikrobearbeitung von fotostrukturierbaren Glasern wird die Eigenschaft Fotosensibilitat im UV-Bereich ausgenutzt. Als „fotosensibel” gilt ein Glas u. a. dann, wenn es unter Einfluss raumlich begrenzter energiereicher UV-Strahlung und anschliesender thermischer Behandlung nur in den belichteten Bereichen kristallisiert. Die Mikrostrukturierung erfolgt durch anschliesendes nasschemisches Atzen der kristallisierten Bereiche. Die Belichtung fotosensitiver Glaser mittels konventioneller Maskaligner ist gegenwartig Stand der Technik. Ein alternatives Verfahren dazu stellt die Belichtung mittels UV-Laserstrahlung dar. Es werden Zusammenhange zwischen Laserparametern und erzeugten Strukturgeometrien diskutiert. Influence of UV-laser parameters on geometrical structuring of photosensitive glass Glass becomes an increasingly important material in micro system technology. A photosensitive glass crystallisizes partially after UV-exposure and thermal treatment only in exposed areas. The micro structuring of the glass takes place during a wet chemical etch process. The exposure of photosensitive glass by means of Maskaligner is currently state of the art. An alternative method is the UV-laser exposure of photosensitive glass. It will be presented the influence of laser parameters on results of micro structuring prozess.

We report about the possibility to drive mass migration into an azo-based polymer by means of two-photon absorption. A symmetric donor-acceptor-donor structured Y-shape azo-chromophore is specifically synthesized to enhance two-photon absorption in the polymer. Features resulting from two-photon absorption in the near-infrared show sub-diffraction limit linear dimensions (250nm).

We have successfully fabricated in vitro femtosecond laser micro‐incisions inside cornea and—for the first time—inside sclera mildly pre‐cleared by a biocompatible and clinically safe (non‐toxic) natural agent (replacive refractive index‐matching 40%‐glucose solution in water), with the tissues taken as fresh cool cuts of human cadaver eyes, and reported on basic operational conditions of the micro‐surgical procedures.

The development of fs laser technology has enabled the internal modification of transparent solid materials, performed by focusing femtosecond (fs) pulses. Using internal modification and subsequent wet etching, micrometer-scale removal processing with arbitrary three-dimensional design was enabled. We applied this technique to transparent nonphotosensitive crystalline and glassy materials. This is a unique processing technique almost impossible by other techniques.The development of fs laser technology has enabled the internal modification of transparent solid materials, performed by focusing femtosecond (fs) pulses. Using internal modification and subsequent wet etching, micrometer-scale removal processing with arbitrary three-dimensional design was enabled. We applied this technique to transparent nonphotosensitive crystalline and glassy materials. This is a unique processing technique almost impossible by other techniques.

In this paper report that micro-grating structures are holographically encoded in SiO/sub 2/ thin films on Si by colliding a pair of pulses split from a single high peak power fs-laser pulse using a Ti:sapphire laser.

In recent years, broadband fiber interferometers have become very popular as basic instruments used in optical low-coherence reflectometry for diagnostics of fiber and integrated optics devices or in optical coherence tomography (OCT) for imaging applications in the biomedical field. The longitudinal resolution of such instruments is inversely proportional to the optical bandwidth of the light source. Broadband luminescence from transition-metal-ion doped materials can significantly improve the longitudinal resolution compared to superluminescent diodes, but the low brightness of its luminescence typically leads to a low dynamic range in OCT. Femtosecond lasers based on, e.g., Ti:sapphire have, therefore, been used as large-bandwidth high-brightness light sources, and subcellular imaging has been demonstrated in this way. Since current femtosecond light sources do not necessarily meet the requirements of compactness, ease of use, and low cost, a suitable light source for OCT is still not available. We have demonstrated the suitability of a superluminescent Ti:sapphire crystal as a light source in the wavelength region 700-1000 nm for OCT with ~2 µm axial resolution [1]. Single spatial mode, fiber coupled output powers of ~40 µW can be generated using a 5 W pump. Guiding of the fluorescence in planar-waveguide geometry can further increase the single-mode fluorescence output powers [2]. Ultimately, in a channel-waveguide geometry that we have successfully created in Ti:sapphire [3], the coupling efficiency of fluorescence emission into a single-mode fiber is expected to further increase to the mW level. The significantly improved sensitivity that will result at this fluorescence power may allow for rapid in vivo ultrahigh-resolution OCT with a simple broadband light source. [1]A. Kowalevicz et al., Opt. Express 10, 349 (2002) [2]M. Pollnau et al., Opt. Lett. 26, 283 (2001) [3]A. Crunteanu et al., Appl. Phys. B, accepted