The Temperature Dependence of Homogeneous and Inhomogeneous Vibrational Linewidth Broadening Studies Using Coherent Picosecond Stokes Scattering

Abstract

The theoretical interpretation of vibrational dephasing experiments has been dependent on several simplifying assumptions [1]. One important assumption has been low depletion (≤5%) of the laser pump in the stimulated Raman excitation process. We have observed that, given exponential stimulated Stokes gain and pulse intensity fluctuations from passively mode-locked Nd:glass laser systems, maintaining stimulated Stokes conversions between 1–5% is a nearly impossible task. Figure 1 shows that immediately after the stimulated Raman scattering threshold is reached, the laser can be depleted ≥10% and depletion approaches ≈50% as the laser energy increases. Other studies measuring both laser and Stokes pulses after the Raman cell reveal coincident sharp thresholds for stimulated Stokes scattering and laser depletion [2]. Consequently, we believe that most vibrational dephasing experiments [3–6] have been performed in the high Stokes conversion regime.