Filamentary Deposition of Laser Energy in Glasses with Bessel Beams

International audienceThe controlled laser energy deposition in dielectrics is a key technological issue for applications thatrequire drilling or structuring glass materials in the bulk. High angle Bessel beams delivered by a fem-tosecond laser have been used for extremely high aspect ratio nanochannels drilling and microstructuringin glass with a single laser shot [1,2]. Several types of filamentary damages were obtained with highangle Bessel beams and were reported to depend on laser pulse duration and energy [2]. I will addressthe question of optimal laser parameters for nonlinear absorption of laser energy in the bulk of dielectricmaterials, along the focal line of a Bessel beam.A semi-analytical model was developed for modeling the generation of a plasma column with fem-tosecond and picosecond laser pulses focused by a conical lens in dielectrics. The associated nonlinearabsorption of energy was calculated so as to highlight the influence of the pulse duration, laser pulseenergy and cone angle, on laser energy absorption. From a map of the density of nonlinear absorption oflaser energy in BK7 as a function of pulse duration and peak fluence, a specific pulse duration is shownto correspond to the highest nonlinear absorption at given pulse energy and cone angle. This durationcorresponds to a transition between two propagation regimes of the laser pulse featured by uniform ornon-uniform laser energy deposition in the Bessel zone. A uniform energy deposition is obtained in theabsence of pulse temporal dynamics.I will show that transmission measurements in BK7 are qualitatively well reproduced by the results ofthe semi-analytical model, which is also in agreement with numerical simulations of the nonlinear pulsepropagatio