Investigation of Nonthermal Population Distributions with Femtosecond Optical Pulses

Abstract

Advances in femtosecond optical pulse techniques have provided a unique opportunity to excite and probe nonthermal population distributions in semiconductors and complex molecular systems. In this talk we will review the current state of high resolution femtosecond and high repetition rate optical pulse techniques and application to the dynamics of nonthermal excitations. Using nigh resolution time resolved absorption spectra we have been able to observe the time evolution of a nearly monoenergetic population of carriers in a semiconductor, excited with a short optical pulse, to a carrier distribution in which a temperature can be defined. In GaAs this process is observed to take place within 150 femtoseconds following excitation. In addition we will discuss measurements of spectral hole burning in a large molecule resulting from excitation of a nonequilibrium distribution of molecules excited by a femtosecond optical pulse.