A DETAILED EXAMINATION OF STIMULATED PUMP-PROBE MEASUREMENTS OF VIBRATIONAL POPULATION RELAXATION

We have developed and demonstrated a pump-probe laser spectroscopic sc heme to measure ground state vibrational population relaxation. There are two significant advantages to this technique over alternative meas urement methods. The first is that the detection sensitivity of the pu mp-probe method is limited by the shot noise present on the probe lase r and the second is that, because of the manner in which the ground st ate vibration(s) are populated, it is possible to interrogate T-1 proc esses for degenerate donor-acceptor conditions. We detail in this arti cle the form of the experimental stimulated signal, the effect of the detection scheme used, and the consequences of spontaneous (Boltzmann) population of ground state vibrations. A central conclusion of this w ork is that, even for small signal limit pump-probe experiments, absor ption, stimulated emission, and spontaneous emission all play importan t roles in collectively determining the form of the experimental signa l. (C) 1996 American Institute of Physics.