Optimizing energy absorption for ultrashort pulse laser ablation of fused silica

We investigate the ultrafast absorption of fused silica irradiated by a single 500 fs laser pulse in the context of micromachining applications. As the absorption of the laser energy is rapid (∼fs), the optical properties of the material evolve during the laser pulse, thereby yielding a feedback on the dynamics of absorption and consequently on the amount of energy that is absorbed. Through complete investigation of energy absorption, by combining “pump depletion” and “pump-probe” experiments in a wide range of incident fluences above the ablation threshold, we demonstrate the existence of an optimal fluence range, enabling to turn transiently the material into a state such that each photon is optimally utilized for ablation.