Abstract

The gain dynamics of photoexcited chromium-doped forsterite (Cr⁴⁺:Mg₂SiO₄) were measured by means of a pulsed excite-and-probe technique. The nonradiative relaxation time within the 3T2 vibronic state was determined by measuring the change in the induced gain of the probe pulse as a function of the pumpprobe delay. A 30 ps, 1.064 m pulse from a mode-locked Nd:YAG laser was split into two beams. The first beam provided the pump pulse to populate the 3T2 manifold. The other beam was focused in a calcite crystal to generate a 1.2 m probe pulse by means of stimulated Raman scattering. The transient gain was determined from the measured ratio of the transmitted probe intensity for unpumped and pumped cases as a function of the pumpprobe delay. The rise time (time for growth of the gain from 10% to 90%) was calculated to be 50 ps. A rate-equation analysis of population in the various states was used to extract a value for the vibrational relaxation time from the experimental data under the assumption of Gaussian pump and probe pulses. The best fit to the experimental data of gain as a function of time yields a value of 10 5 ps for the intra-3T2-state vibrational relaxation time.

© 1990 Optical Society of America