Spot Arrays for Uniform Material Ablation with Ultrashort Pulsed Lasers

Abstract

Working with spot arrays for ultrashort pulsed laser materials processing provides a structured method of averaging to overcome speckle noise during phase-only beam shaping. The targeted pattern is divided into several arrays of spots where adjacent spots within the same pattern are separated far enough to not interfere with each other. We show that a pulse-by-pulse change of the individual spot arrays during material ablation is crucial to achieve a uniform surface of high quality. Furthermore, the amount of ablated material and thus the ablation efficiency increases by a factor of 2 when each laser pulse is shaped with another spot pattern. Since phase-only beam shaping devices are technically limited to frame rates around 30 Hz to 60 Hz, they strongly limit the switching time between independent spot patterns and thus decrease the overall efficiency. Therefore we develop an optical setup with a control system that provides a modulation frequency of almost 600 Hz with the prospect of achieving even higher values around 10 kHz with dedicated hardware and tuning.

Keywords: LCoS SLM, phase-only beam shaping, spot array, ultrashort pulsed laser materials processing