Simulation of Light-Matter Interaction and Two-Photon Absorption Induced Charge Deposition by Ultrashort Optical Pulses in Silicon

Nonlinear beam propagation software is used to calculate quantitatively the two-photon absorption (TPA)-induced charge-density profiles generated in silicon by focused femtosecond laser pulses under conditions that are experimentally relevant for single-event effects studies. The described approach permits simulation and prediction of the impact of various optical nonlinearities on the beam propagation through, and generation of free carriers in silicon for F/#s approaching one. It is found that, even at moderate incident laser pulse energies, the nonlinear-optical processes of nonlinear refraction, free-carrier absorption, and free-carrier refraction all contribute, and must be considered in describing the TPA-induced charge generation in silicon. Free-carrier refraction is found to play the dominant role in distorting the charge density profile at larger pulse energies. The simulation results are validated with experimentally measured beam sizes for different focusing conditions.