The recent advancement of industrial-grade femtosecond laser systems with high harmonics modules expands the range of usable laser sources for direct laser ablation using UV laser pulses. It is well known that shorter pulse processing, due to characteristic pulse timescales smaller than the processing material’s atomic vibrations timescale, has reduced heat-affected zones (HAZ), which causes better ablation precision compared to the longer pulses. This leads to a lower surface roughness of an ablated region, and, most importantly, as the absorption remains linear, the roughness and ablation depth can be directly controlled. Another advantage of using UV instead of longer wavelengths is that there is a wide choice of materials to work with because many materials absorb UV. The choice of laser beam parameters and patterning algorithm is very important and optimal parameters varies with respect to a chosen material and applications. However, there are still some struggles to correctly predict the ablation depth and surface roughness required for the fabrication of diffractive optical elements, microfluidic chips, hydrophobic surfaces, and other devices.

In this study we present femtosecond pulsed laser [206 nm, 50 kHz, 210 fs] ablation results on BK7 glass, Sapphire and LiNbO3. We are using Yb:KGW laser system (PHAROS Light Conversion) with 5th harmonic generator, Aerotech ANT180 micro positioning system and calcium fluoride lenses for beam focusing. The experimental setup lets us fabricate good quality grooves with low heat affected zones without any post-processing. By optimizing laser fluence distribution we can choose a proper fabrication parameter set which lets us achieve surface roughness in the order of tens of nanometers.