Time dynamics of burst-train filamentation assisted femtosecond laser machining in glasses

TLDR

The authors used a resonator to generate 38.5 MHz femtosecond pulse bursts, released into controlled profiles by a Pockels cell, to drive filamentation‑assisted machining of high‑aspect‑ratio holes in transparent glass while recording time‑resolved side‑view images from 2 ns to 400 ms to study hole formation and plume dynamics. Transient photoluminescence and plume emissions show heat accumulation, filament formation, and plume shielding during burst‑train machining, and the short pulse interval reduces shock‑induced microcracks relative to single‑pulse processing.

Abstract

Bursts of femtosecond laser pulses with a repetition rate of f = 38.5MHz were created using a purpose-built optical resonator. Single Ti:Sapphire laser pulses, trapped inside a resonator and released into controllable burst profiles by computer generated trigger delays to a fast Pockels cell switch, drove filamentation-assisted laser machining of high aspect ratio holes deep into transparent glasses. The time dynamics of the hole formation and ablation plume physics on 2-ns to 400-ms time scales were examined in time-resolved side-view images recorded with an intensified-CCD camera during the laser machining process. Transient effects of photoluminescence and ablation plume emissions confirm the build-up of heat accumulation effects during the burst train, the formation of laser-generated filaments and plume-shielding effects inside the deeply etched vias. The small time interval between the pulses in the present burst train enabled a more gentle modification in the laser interaction volume that mitigated shock-induced microcracks compared with single pulses.