Influence of working parameters on multi-shot femtosecond laser surface ablation of lithium niobate

Abstract

• The incubation effect was observed during multi-shot fs-laser pulses at different pulse repetition rates and was modelled using a power law. • The single pulse ablation threshold F th , 1 and the asymptotic ablation threshold F th , ∞ were evaluated and were found consistent with values reported in existing literature. • The impact of laser operational variables on the surface roughness and milled depth of fs-laser micromilled zones on LiNbO 3 substrates was investigated. • A trade-off between control over the obtained depth and the surface finish of the process was found. This paper presents an experimental investigation on the ultrashort pulsed laser ablation of 128 ° Y-cut Lithium Niobate (LiNbO 3 ) using multi-shot fs-laser pulses at different pulse repetition frequencies (1, 10 and 100 k H z ). The ablation threshold fluence was observed to rapidly decrease as the number N of incident laser pulses increased, regardless of the repetition frequency. This behavior, compatible with the incubation effect, was accurately modeled by a power law. The calculated single pulse ablation threshold F th , 1 = 1.98 ± 0.15 J / c m 2 is consistent with values reported in existing literature. The incubation coefficient S ∗ appears to be independent of the repetition frequencies. In contrast, the asymptotic ablation threshold F th , ∞ decreased as the repetition frequency was increased. The study delves deeper into the impact of laser operational variables, including pulse energy, repetition frequency, total pulse count, and scanning speed, on the surface roughness and milled depth of fs-laser micromilled zones on LiNbO 3 substrates. A discernible trade-off between achieving control over the obtained depth and the surface finish of the process was identified, providing valuable insights for achieving precise control over fs-laser processing of LiNbO 3 surfaces.

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