Abstract

We report negative absorption saturation dropping observed in femtosecond pump-probe measurements for GaAs at 80 as well as 300 K. This probability arises from the band gap renormalization in the presence of photoexcited electron-hole plasma. Band gap renormalization together with band filling causes some difficulties in analysis of the carrier cooling dynamics from the pump-probe traces obtained with single wavelength laser pulses. Although the dynamics of band gap renormalization in GaAs has been studied by Shank et al.,¹ its effects on the femtosecond pump-probe measurements, however, have not been explored experimentally. On the other hand, the observed negative absorption saturation reflects the temporal evolution of the band gap renormalization. Experimental results show that band gap renormalization occurs within 1 ps after excitation in GaAs at low temperature. This is consistent with that observed in Ref. 1.

© 1990 Optical Society of America