Intense photoexcitation of a semiconductor using femtosecond laser pulses affects its optical properties. We consider the transient photoinduced changes Delta epsilon to the dielectric function epsilon of bulk Ge after excitation with 100-fs laser pulses at 1.5 eV creating a carrier density of 4 x 10(18) cm(-3) due to three mechanisms : (i) diffusion of carriers from the surface into the bulk, (ii) relaxation of carriers in momentum space, and (iii) many-body effects, including band gap renormalization, collisional broadening, screening of the excitonic Coulomb enhancement, and band filling.