Femtosecond laser micromachining of dielectrics using double pulse Gauss-Bessel beams
Résumé
Direct laser writing is a very useful technique to process dielectrics for many applications, like micro-fluidics, photo-electronics or glass cutting for consumer electronics. Material processing requires accurate control on energy deposition profiles inside the transparent material, which strongly depends on irradiation conditions. Gauss-Bessel beams have been successfully used for ultra-high aspect ratio processing because of the enhanced stability of these beams in comparison with the unstable and complex filamentation regime of Gaussian beams. In this work, we temporally split the input 100 fs laser pulse in two equal pulses with a variable delay. We compare single and double pulse illumination as a function of delay on the drilling of high aspect ratio nanochannels in borosilicate glass. Our main result is that, with equal energy, splitting the pulse allows increasing the channel width and enables channel drilling for conditions when only index modification was created. The results strongly depend on the sub-nanosecond delay (ie at delays below the standard burst mode of lasers). We report measurements of energy absorption and interpret our results in terms of confinement of the energy deposition. Our results raise novel fundamental questions on laser-matter interaction and we anticipate a wide impact on technological applications to laser processing of transparent materials.