A RELIABLE PUMP-PROBE, BROAD-BAND SPECTROMETER FOR SUBPICOSECOND TRANSIENT ABSORPTION

A pump-and-probe spectrometer is described that employs a pump pulse at 308 nm, with up to 1.4 mJ in 250 fs, and a continuum probe pulse in the spectral range 360-750 nm, of 80-fs pulse duration. The corresponding laser system is based on a colliding-pulse-mode dye laser operating at 616 nm, and a fs dye laser amplifier pumped by a XeCl* excimer laser. The amplifier has been designed specifically for pump-and-probe experiments, by multiplexing with horizontally and vertically polarized pulses for the pump and probe beam, respectively. Near-diffraction-limited output beams are achieved using a novel, capillary prismatic dye amplifier cell. The reliability of the apparatus is demonstrated by examining the photodissociation of bis-(p-aminophenyl) disulfide. The absorption band of the resulting p-aminophenyl-thiyl radicals shows a biexponential frequency shift in the course of several ps. This behavior is correlated with that of dielectric relaxation of the solvent.