Abstract

Femtosecond optical pulses are a valuable tool in elucidating the ultrafast transfer of light pulse energy to a crystalline lattice, such as in pulsed laser annealing of semiconductors. Previous femtosecond experiments on silicon have measured the changes in reflectivity at the surface of an optically thick sample.^1,2 In the present experiment, we obtain complete time-resolved information on the optical constants of silicon by measuring absorption in an optically thin layer of silicon. The optical absorption between the indirect and direct band gaps is a valuable monitor of the speed and magnitude of lattice temperature rise,³ since this absorption depends strongly on lattice temperature.⁴ In addition, we can determine for the first time the relative importance of nonlinear and linear absorption in femtosecond laser excitation of silicon.

© 1985 Optical Society of America