SCALING OF 4-PHOTON ABSORPTION IN INAS

By monitoring the nonlinear absorption of picosecond laser pulses as a function of lattice temperature, we identify four-photon absorption i n bulk InAs. Optical bandgap scaling of this process is consistent wit h a calculation obtained from fourth-order perturbation theory for all owed-allowed-allowed-forbidden transitions. A model of nonlinear absor ption based on laser-induced impact ionization disagrees with the expe rimental results. (C) 1997 Optical Society of America.