High-resolution stimulated Raman spectroscopy from collisionally populated staes after optical pumping- Acetylene isotopomers

Abstract

We demonstrate a variation of a sequential pump-probe, double resonance stimulated Raman technique in which the optical pumping of population is combined with the naturally occurring process of vibration-to-vibration (V-V) collisional energy transfer. A fraction of the vibrational population initially promoted by the pump stage to the v2=1 excited state of 12C2H2 and 12C2D2, ends up reaching other excited states for which the collisional energy transfer is energetically favourable. After this, the probe (spectroscopy) stage is used to register high resolution spectra of transitions departing from these states. The technique, schematically depicted in Figure 1, requires the optimization of sample pressures and pump-probe delays in order to maximize the amount of population transferred to the excited states one wishes to observe while minimizing the impact of competing processes (molecular diffusion or V-T energy transfer) and still maintain the relatively low pressures necessary to obtain high resolution spectra.