High temporal resolution and calibration in pump–probe experiments characterizing femtosecond laser–dielectrics interaction

Abstract

In the aim of performing pump–probe experiments with a high temporal accuracy, the determination of the perfect temporal overlap of the two incoming pulses is crucial. When addressing laser–dielectrics interaction, this ‘time zero’ is often estimated from the dynamics of interest itself (e.g. when optical changes start). Here, we present an experimental approach to overcome this limitation, enabling in situ determination of the time zero independently from the observed dynamical process. We rely on an adapted frequency-resolved optical gating technique, which provides in addition the complete characterization of the probe pulse, measured directly in the focal plane of interaction. The designed set-up permits the observation of transient dynamics with a temporal sampling resolution smaller by a factor of eight compared to the pump pulse duration. For demonstration, we follow in time the change of transient optical properties at the surface of a fused silica sample irradiated by a single femtosecond pulse, during the pulse itself.