PUMP PROBE SPECTROSCOPY BY ASYNCHRONOUS OPTICAL-SAMPLING

The authors report the first results from a new pump/probe technique called asynchronous optical sampling (ASOPS). The method employs a mode-locked, frequency-doubled Nd:YAG laser operating of a repetition rate of 81. 5970000 MHz as the pump laser, and a synchronously pumped dye laser (R6G) operating at a repetition rate of 81. 5870000 MHz as the probe laser system. The 10-kHz beat frequency produces a repetitive relative phase walk-out of the pump and probe pulses which replaces the optical delay line used in conventional instruments. Studies of rhodamine B in methanol demonstrate that the instrument response is proportional to pump power, probe power, and sample absorptance. The fluorescence lifetime of 4 multiplied by 10** minus **5 M rhodamine B is determined to be 2. 3 ns.