Laser ablation and structuring of transparent materials with ultrashort laser pulses

We have investigated the material processing of oxides and fluorides using ultrashort laser pulses and have demonstrated a strong improvement when compared to results using longer pulse widths in the nanosecond range. High laser fluences (well above the damage threshold) at 800 nm and 248 nm are used to generate channels with high aspect ratios. Careful beam alignment can eliminate any remaining stress-induced damage outside the channel. At intermediate fluences just above the front surface processing threshold we observe a low ablation rate. In this 'gentle etch' phase it is possible to generate well-defined, smooth pockets and periodic patterns or ripples. The ripples appear when the laser pulse width is shorter than the lifetime of the electrons excited into the conduction band. In the low fluence regime (below the surface damage threshold) the self-focusing of laser pulses in the ps and sub-ps range can be utilized to obtain microstructures inside and on the rear side of the transparent materials.