Second Harmonic and Hyper-Rayleigh Generation of (111) silicon wafer

Ultrafast time-resolved THz-induced SHG, also named hyper-Rayleigh generation, is performed at the surface of a (111) silicon wafer upon its excitation by a 50 fs IR optical pulse. The evolution of the SHG spectrum is recorded delaying in time the optical pulse with respect to the THz pulse. Upon excitation, we record a broad Stokes and anti-Stokes bands centered around the Si lattice phonon at ~610 cm
^-1
. The spectral evolution of the SHG signal versus the delay between optical and THz pulses makes it possible to evidence the interference between volume and surface contributions as well as the ultrafast evolution of the hyper-Rayleigh susceptibility upon hot carrier generation.