Laser-induced nonequilibrium electron distribution in metals on a femtosecond time scale

A nonequilibrium distribution function for electrons in metals excited by u ltrashort laser pulses and its relaxation dynamics is analyzed. This distri bution function is based on a kinetic differential equation for the nonequi librium population of excited electrons. The deviation of the distribution function from the equilibrium one can be monitored by femtosecond broadband pump-probe spectroscopy. Transient changes of the dielectric function Delt a epsilon and the relaxation of nonequilibrium charge carriers in a thin go ld film are discussed for different excitation energies (h) over bar omega( pump) that corresponds to intra- or interband excitation or to photoemissio n of the excited electrons.