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 photoexcitation below the threshold fluence Eₜₕ 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 photoexcitation, but becomes faster as Eₜₕ is approached. A model based on delayed Auger heating is presented.