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MANUFACTURING with short pulse lasers
BURST MACHINING OF BANDGAP MATERIALS- SEMICONDUCTORS Materials featuring a bandgap such as semiconductors and dielectrics have longer thermal diffusion times and are thus extremely well-suited for taking advantage of burst-mode processing which is based on beneficial and controlled heat accumulation. For bandgap materials, bursts should typically contain several tens or hundreds of sub-pulses.
The burst-mode constitutes a very interesting and promising approach for in-bulk modifications with femtosecond pulses in semiconductors. These materials are characterized by a very high non-linear index that prevents localized energy deposition at the focal point. Thus, distributing the energy over many sub-pulses constituting a burst is a suitable strategy for overcoming the limitations observed with repetitive ultra-short single pulses. The group of David Grojo in Marseille recently carried out pioneering work based on THz-bursts for semiconductor processing, for example on Gallium Arsenide, where bursts formed by an array of subsequent birefringent crystals of different lengths were used [ 3 ]. Figure 3 shows luminescence microscopy images for single pulses and bursts with increasing number of sub-pulses( pulse duration and pulse spacing are 180 fs). Image S corresponds to the longest pulse train containing 64 sub-pulses and shows intense and very localized luminescence confirming successful and localized energy deposition with this approach.
BURST MACHINING OF BANDGAP MATERIALS- DIELECTRICS For dielectrics, longer inter-pulse delays between the sub-pulses can be very efficient as the heat diffusion time scales are much longer than in semiconductors. MHz-bursts have been investigated for glass processing for more than two decades, in early times since 1999, with
Figure 2. Example of efficient laser milling.( a) Optical image of laser milled coat of arms of Lithuania in a copper plate.( b),( c) SEM images of laser-milled surface illustrating high quality layer-by-layer removal. Reproduced under the terms of a Creative Commons Attribution 4.0 International License,( https:// creativecommons. org / licenses / by / 4.0 /( accessed on 04 March 2026)) [ 2 ]. Copyright 2019, the authors, published by Springer Nature.
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