THEORY OF FEMTOSECOND ELLIPSOMETRY IN GE AT 1.5 EV

Intense photoexcitation of a semiconductor using femtosecond laser pul ses affects its optical properties. We consider the transient photoind uced changes Delta epsilon to the dielectric function epsilon of bulk Ge after excitation with 100-fs laser pulses at 1.5 eV creating a carr ier density of 4 x 10(18) cm(-3) due to three mechanisms: (i) diffusio n of carriers from the surface into the bulk, (ii) relaxation of carri ers in momentum space, and (iii) many-body effects, including band gap renormalization, collisional broadening, screening of the excitonic C oulomb enhancement, and band filling. (C) 1998 Elsevier Science S.A.