INTERFERENCE EFFECTS IN PUMP-PROBE SPECTROSCOPY OF THIN-FILMS

A method of obtaining the complex change in dielectric constant DELTAe psilon from values of the photoinduced change in reflection DELTAR/R a nd transmission DELTAT/T measured via pump-probe spectroscopy is prese nted. By solving Maxwell's equations perturbatively in the small DELTA epsilon limit, we show that the nonuniformity of the pump absorption p rofile must be taken into account in order to obtain an accurate measu rement of DELTAepsilon. A method for removing artifacts due to thin-fi lm interference fringes is also presented. The results are applied to picosecond photomodulation studies of amorphous hydrogenated semicondu ctor films.