Direct detection of ultrafast thermal transients by use of a chirped, supercontinuum white-light pulse

An experimental technique is demonstrated that permits direct optical measu rement of ultrafast material transients during a single excitation-relaxati on cycle. Reflection of a linearly chirped, supercontinuum optical pulse fr om a gold film with changing surface temperature induced by an ultrafast pu mp pulse allows the thermal transients to be encoded onto the spectrum of t he probe pulse. Calibrating the chirp of the probe pulse and the wavelength sensitivity of the sample permits mapping of the measured transient into t he time domain. Measurements are completed over the course of 100 ps with s ubpicosecond time resolution. Results obtained with this technique are comp ared with similar measurements obtained with conventional pump-probe correl ation techniques. (C) 2001 Optical Society of America.