Excitation of the electronic subsystem of silicon by femtosecond laser irradiation

We have studied processes initiated in the bulk of singlecrystal silicon by local excitation of its electronic subsystem with femtosecond IR laser pulses ({lambda} = 1.2 {mu}m, {tau}{sub FWHM} = 250 fs). IR femtosecond interferometry has been used for the first time to measure the refractive index of the irradiated zone. Using the interference images obtained in our experiments, we have reconstructed the dynamics of the electron - hole plasma generated near the axis of a focused laser beam. Experimental data have been compared to relevant numerical simulation results obtained in a simple, two-photon absorption model. (interaction of laser radiation with matter)