Approach for high precision ultrashort pulsed laser deep ablation for the generation of macroscopic freeform 2.5D structures in fused silica

We report on deep laser ablation of fused silica using ultrashort pulses at a high pulse frequency rate of 1000 kHz, enabling highly precise and fast generation of 2.5D structures, such as, e.g., optical elements and microfluidic elements. Depending on the specific demands of such applications in terms of surface roughness and geometrical features, initially the applied fluence is finely chosen in conjunction with the scan velocity and a fine refocusing to ablate defined layer heights even across larger ablation depths. Specifically, our approach allows a consistent layer-wise ablation of 1 µm down to at least 1900 µm with an error of below 0.5 % with respect to the targeted depth. In addition, angles between 0.2 ∘ and 67.5 ∘ can be precisely realized with a superior mean angle error of below 0.1 ∘ . To exemplify the potential of this sophisticated approach, we generate an Alvarez-like freeform lens structure with high geometrical accuracy.