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.
Highlights
Ultrashort laser pulses are used to modify many kinds of transparent materials where the advantages of high-intensity nonlinear absorption are most advantageous to drive controllable processing in otherwise highly robust materials
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
High-aspect ratio holes in diverse materials were created using various methods of laser processing: One method is the statically exposure with single femtosecond laser pulses focused at the front side [8] or the rear side of a glass sample which in the latter case was in contact with a liquid [9]
Summary
Ultrashort laser pulses are used to modify many kinds of transparent materials where the advantages of high-intensity nonlinear absorption are most advantageous to drive controllable processing in otherwise highly robust materials. Scanning methods have been investigated like longitudinally scanning along the beam propagation direction from the rear surface of silica glass [10] Another method for surface treatment is laser-induced back-side wet etching of fused silica which was realized using excimer laser radiation obtaining high quality etched surfaces with micropatterns [11]. Beside glass materials even metalloids like silicon wafers have been processed with a helical drilling method where smooth holes were fabricated with pulses of 10ps pulse duration [13]. In this case the processing time exceeds t = 100s for optimal drilling results
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