Ultrafast heating of silicon-on-sapphire by femtosecond optical pulses.

We monitor the refractive index n + ik of an optically thin silicon layer following femtosecond photo-excitation below the threshold fluence E(TH) for melting in order to measure the rate of lattice temperature rise. We find that most of the heating is delayed with respect to the photo excitation, but becomes faster as E(TH) is approached. A model based on delayed Auger heating is presented.