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Stuttgart, Germany

Zhang D.,University of Duisburg - Essen | Gokce B.,University of Duisburg - Essen | Sommer S.,Dausinger + Giesen GmbH | Streubel R.,University of Duisburg - Essen | Barcikowski S.,University of Duisburg - Essen
Applied Surface Science | Year: 2016

In this paper, we perform liquid-assisted picosecond laser cutting of 150 μm thin germanium wafers from the rear side. By investigating the cutting efficiency (the ability to allow an one-line cut-through) and quality (characterized by groove morphologies on both sides), the pros and cons of this technique under different conditions are clarified. Specifically, with laser fluence fixed, repetition rate and scanning speed are varied to show quality and efficiency control by means of laser parameter modulation. It is found that low repetition rate ablation in liquid gives rise to a better cut quality on the front side than high repetition rate ablation since it avoids dispersed nanoparticles redeposition resulting from a bubble collapse, unlike the case of 100 kHz which leads to large nanorings near the grooves resulting from a strong interaction of bubbles and the case of 50 kHz which leads to random cutting due to the interaction of the former pulse induced cavitation bubble and the subsequent laser pulse. Furthermore, ethanol is mixed with pure distilled water to assess the liquid's impact on the cutting efficiency and cutting quality. The results show that increasing the ethanol fraction decreases the ablation efficiency but simultaneously, greatly improves the cutting quality. The improvement of cut quality as ethanol ratio increases may be attributed to less laser beam interference by a lower density of bubbles which adhere near the cut kerf during ablation. A higher density of bubbles generated from ethanol vaporization during laser ablation in liquid will cause stronger bubble shielding effect toward the laser beam propagation and therefore result in less laser energy available for the cut, which is the main reason for the decrease of cut efficiency in water-ethanol mixtures. Our findings give an insight into under which condition the rear-side laser cutting of thin solar cells should be performed: high repetition, pure distilled water and high laser power are favorable for high-speed rough cutting but the cut kerf suffers from strong side effects of ripples, nanoredeposition occurrence, while low laser power at low repetition rate (10 kHz), mixed solution (1 wt% ethanol in water) and moderate scanning speed (100 μm/s) are preferable for ultrafine high-quality debris-free cutting. The feasibility of high-quality cut is a good indication of using rear laser ablation in liquid to cut thinner wafers. More importantly, this technique spares any post cleaning steps to reduce the risk to the contamination or crack of the thin wafers. © 2016 Elsevier B.V. All rights reserved. Source

Schuhmann K.,ETH Zurich | Larionov M.,Dausinger + Giesen GmbH
Optics InfoBase Conference Papers | Year: 2013

A frequency-doubled single-frequency disk laser demonstrates 30 W output at an efficiency of 30 % using a VBG with 4 % loss in a coupled cavity, reducing its thermal load and loss. © OSA 2013. Source

Borchers B.,Coherent GmbH | Schafer C.,Coherent GmbH | Fries C.,Photonik Zentrum Kaiserslautern E.V. | Larionov M.,Dausinger + Giesen GmbH | Knappe R.,Coherent GmbH
Advanced Solid State Lasers, ASSL 2015 | Year: 2015

We present a novel two-crystal approach rendering polarization rotation mode-locking via cascaded χ2-nonlinearities applicable to broadband lasers sources. This technique is demonstrated at a thin disk oscillator reaching >40W average power and <500fs pulse duration. © OSA 2015. Source

Abt F.,FGSW Forschungsgesellschaft fur Strahlwerkzeuge gGmbH | Blug A.,Fraunhofer Institute for Physical Measurement Techniques | Nicolosi L.,Iee Institute Fuer Grundlagen Der Elektrotechnik U Elektronik | Dausinger F.,Dausinger + Giesen GmbH | And 3 more authors.
Journal of Laser Micro Nanoengineering | Year: 2011

Camera based in-process control for laser welding enables flexible image processing which allows the adaption of the system to different processes and quality features. A closed loop control system with a Cellular Neural Network Camera was implemented into a laser welding machine. The system is surveying the contour of the full penetration hole with a frame rate of over 10 kHz for both, acquisition and evaluation of area images. As a result the system reaches and holds the full penetration state automatically. This paper shows the latest experimental results including the extension to direction independent weldings. Source

Dausinger + Giesen GmbH | Entity website

An example for D+G special purpose laser systems is our VaryDisk laser system. The VaryDisk is a fully functional laser system designed for laboratory investigations and/or industrial use ...

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