Time-resolved investigations of laser-dielectric interaction mechanisms

Laser processing and machining of dielectrics is a growing field, involving increasingly complex laser temporal and spatial pulse shaping. Predicting and modeling the optimum pulse characteristic for a given application requires a detailed knowledge of all the elementary events involved during the interaction. To understand and observe these physical mechanisms in detail, we carry out different time resolved experiments: spectral interferometry, holography, reflectivity change and photoelectron spectroscopy. Thus, we can measure in real time the excitation density achieved in the solid and the following relaxation of excited carriers. Since many processes (non-linear excitation, impact ionization, modification of pulse shape and propagation) arise during the pump laser pulse itself, usual pump-probe experiments are not capable to distinguish and directly observe them. To encompass this difficulty, we used a flexible double pump scheme [1], allowing modulating the excitation density and controlling the carrier heating steps.