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Die Fertigung von mikrofluidischen Strukturen fur die Analyse von chemischen und biochemischen Probeneigenschaften im Rahmen eines optischen "Lab-on-a-Chip" erfordert Herstellungsmethoden, mit welchen reproduzierbare, qualitativ hochwertige Ergebnisse erzielt werden konnen. Im Rahmen der Erforschung dieser Komplettanalysesysteme (Micro Total Analysis Systems) ist es jedoch oftmals von Interesse, die einzelnen Teilfunktionen auf eigenen Plattformen zu testen und zu optimieren. In diesem Beitrag werden zwei Rapid Prototyping-Methoden vorgestellt, welche eine schnelle und prazise Fabrikation solcher Teilprototypen ermoglichen: Mikro-Stereolithographie und Femtosekunden-Laserablation. Auf der Grundlage von fluiddynamischen Finite-Elemente-Modell-Simulationen wird ein neuartiger optischer Mikrofluidik-Chipentwurf prasentiert und anhand von optischen Messungen charakterisiert.

We have demonstrated micromachining of bulk 3C silicon carbide (3C- SiC) wafers by employing 1028nm wavelength femtosecond laser pulses of energy less than 10 nJ directly from a femtosecond laser oscillator, thus eliminating the need for an amplified system and increasing the micromachining speed by more than four orders of magnitude.

Laser treatment of bone tissue has already been the subject of many studies to find substitutes for mechanical instruments that are nowadays used in implantology and orthopaedics. Mainly lasers with pulse durations in the μs region have been tested leaving surface features that are not always satisfactory. Therefore, in the present study laser osteotomy has been performed with a 330 fs Yb:glass laser, λ = 1040 nm, at a pulse repetition rate of 1 kHz. For bovine spongiosa, compacta, and cartilage, the ablation thresholds as well as the ablation rates for various pulse energies have been determined. Additionally, quadratic areas have been ablated in bone tissue. The remaining morphology has been analyzed via scanning electron microscopy. Laser ablation has also been performed with an Er, Cr:YSGG laser, λ = 2780 nm, PRR = 20 Hz, τ ∼ 50 μs. The results of USPL and Erbium laser ablation are compared.

We have investigated the ablation behaviour of single crystal SrTiO3 with focus on the influence of the pulse duration at a wavelength of 248 nm. The experiments were performed with KrF-excimer lasers with pulse durations of 34 ns and 500 fs, respectively. Femtosecond-ablation turns out to be more efficient by one order of magnitude and to eliminate the known problem of cracking of SrTiO3 during laser machining with longer pulses [1],[2]. In addition, the cavities ablated with femtosecond pulses display a smoother surface with no indication of melting and well-defined, sharp edges. These effects can be explained by the reduced thermal shock effect on the material by using ultrashort pulses.

We have performed a comparative study of UV laser ablation of SrTiO3 with nanosecond- and sub-picosecond sources, respectively. The experiments were performed with lasers at a wavelength of 248 nm and pulse durations of 34 ns and 500 fs. Femtosecond ablation turns out to be more efficient by one order of magnitude and eliminated the known problem of cracking of SrTiO3 during laser machining with longer pulses. In addition, the cavities ablated with femtosecond pulses display a smoother surface with no indication of melting and well-defined, sharp edges. These effects can be explained by the reduced thermal shock effect on the material by using ultrashort pulses.

We present ablation results of silicon obtained by simultaneous irradiation of the sample with the fundamental beam of a picosecond-neodymium-vanadate (Nd:VAN) laser (1064 nm, 10 ps pulse duration) and a small amount of second harmonic (SH) produced in a thin nonlinear crystal. In this fashion, the ablation yield could be increased by 70%. In addition, the ablation quality was improved in terms of surface smoothness. The underlying mechanism can be attributed to a ‘seeding’ of the target area with free carriers by the 532 nm radiation.

We demonstrate surface micromachining of bulk 3C silicon carbide (3C-SiC) wafers by employing tightly focused infrared femtosecond laser pulses of energy less than 10 nJ directly from a femtosecond laser oscillator, thus eliminating the need for an amplified system and increasing the micromachining speed by more than four orders of magnitude. In addition, we show that high aspect ratio through-tapered vias can be drilled in 400 µm thick wafers using an amplified femtosecond laser.

We report on recent results on selective ablation of TCO (SnO2, ZnO) and metallic layers as a possible process for structuring thin film solar cells. The multipulse ablation thresholds determined for substrate and various thin films show a parameter window where the films can be completely removed by a single scan without at the same time damaging the underlying material. By employing ultrashort pulsed lasers, nonthermal ablation at repetition rates up to the megahertz regime enables high quality structuring combined with process speeds meeting industrial demands.

In this paper we present the design, simulation and measurement results of a novel sensor system fabricated by femtosecond pulsed laser prototyping. To our knowledge this is the first time an entire optical microfluidic chip with sample flow control is manufactured in SU-8 by ultra short pulsed laser ablation. Almost free of any heat load to the material, it allows resist structuring with high resolution and good edge definition. The fluid dynamic analysis carried out in this work provides the design and measurement parameters for an integrated optical analysis system for particle detection. An enhancement of previously presented systems is obtained by a different side port design which improves the quality of the sample flow shape. Our design also allows measuring fluorescence and optical absorption via fiber coupled laser source and photo detectors.

Femtosecond laser pulses permit laser ablation almost free of any heat load to the material, which allows the structuring of various materials with high resolution and good edge definition. We present recent results on selective laser ablation of thick photoresists (AZ-Types) from dielectric substrates as a critical process step in MEMS (micro electromechanical systems) fabrication, capitalizing on the different ablation thresholds of the resist layer and the substrate material. The laser used was an ultrafast pulsed Yb:glass regenerative amplifier with a pulse duration of 300 fs.

In dental hard tissue ablation, ultra-short laser pulses have proven sufficiently their potential for material ablation with negligible collateral damage providing many advantages. The absence of microcracks and the possibility to avoid overheating of the pulp during dental cavity preparation may be among the most important issues, the latter opening up an avenue for potential painless treatment. Beside the evident short interaction time of laser radiation with the irradiated tissue, scanning of the ultra-short pulse trains turned out to be crucial for ablating cavities of required quality and shape. Additionally, such a technique allows to treat larger areas like the ones dentists are used to work with, i.e. ~ 1 mm O.In this paper, an overview of different scanning methods together with the algorithms used and an assessment of their applicability is presented. A variety of pulse durations from ~100 fs up to several ps has been used by numerous authors over the last approximately ten years. Having employed 330 fs pulses, we present the corresponding ablation thresholds for dental hard tissue (enamel, dentine; human and bovine), for a number of dental restoration materials, as well as for different types of bovine bone. Dental implants frequently have to be cleaned from plaque being deposited around their necks in areas where the gums have already retreated. A preliminary investigation is presented on the applicability of ultra-short pulses with mentioned duration for the gentle cleaning of titanium implants focusing on the preservation of the special plasma-sprayed biocompatible implant surface.

We report on recent results of laser ablation in semiconductors obtained by simultaneous irradiation of the sample with a superposition of the fundamental beam of a picosecond-Neodymium-Vanadate (Nd:VAN) laser (1064 nm, 10 ps pulse duration) and a small fraction of its second harmonic (SH) produced in a thin nonlinear crystal. In this fashion, the ablation yield could be increased by 70%. In addition, the ablation quality was improved in terms of surface smoothness. The underlying mechanism can be attributed to a 'seeding' of the target area with free carriers by the 532 nm radiation.