Time-resolved dynamics of ultrafast Bessel and Gaussian beam propagation and energy deposition in transparent materials
Résumé
Propagation of high intense ultrafast laser pulses inside transparent materials has a strong influence in microfabrication quality and accuracy in the field of 3D laser-material processing. Concepts of tight focusing or non-diffractive propagation carry in consequence a strong potential. Knowledge of the propagation of Gauss and Bessel beams at the focus where the laser-material interaction regime can sustain for either short or higher propagation distances becomes essential. We study the material interaction with ultrafast Bessel and Gaussian beams at different energy and focusing conditions and their impact in the various photoinscription regimes, i.e. formation of isotropic type-I refractive index structures or non-isotropic nanoscale modulated type II structures. To understand the formation mechanisms of these different interaction regimes, we propose probing the ultrafast dynamics of these structures using time-resolved microscopy and spectral imaging in fused silica. Single and multi pulse measurements around the damage threshold can give information about the relaxation mechanisms leading to permanent refractive index changes accompanied by structure characteristic defect markers. Also we figure out key mechanisms in excitation and relaxation dynamics associated with Gaussian and Bessel beam propagation.