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).

Date Published: 2 March 2020
PDF: 6 pages
Proc. SPIE 11268, Laser-based Micro- and Nanoprocessing XIV, 112681G (2 March 2020); doi: 10.1117/12.2546162

Published in SPIE Proceedings Vol. 11268:
Laser-based Micro- and Nanoprocessing XIV
Udo Klotzbach; Akira Watanabe; Rainer Kling, Editor(s)