Collisional effects on molecular dynamics in electronic-resonance-enhanced CARS

Abstract

The role of collisional decay on the evolution of molecular coherence and excited-state population in an electronic-resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) configuration is studied. A four-level model scheme is proposed and a density-matrix equation is derived to determine the system evolution. It is shown that even for significantly large collisional decays, a suitable (rather strong) probe-laser intensity prevents significant depletion of the excited-state population and enhances the ground-state coherence. A physical understanding is developed for the reported insensitivity [Roy et al. Appl. Phys. Lett. 2006, 89, 104105] of the ERE-CARS signal to the rate of collisional decay at the excited electronic level.

Keywords:

• coherent anti-Stokes Raman scattering
• collision
• electronic quenching
• molecular coherence
• molecular dynamics

Acknowledgements

We are extremely thankful to Dr T.B. Settersten for many interesting discussions on various incoherent processes in NO and for providing us crucial parameters to validate our proposed model for NO. Funding for this research was provided by the Air Force Office of Scientific Research under Contract No. FA9550-07-C-0036 (Dr Julian Tishkoff, Program Manager) and by the US Department of Energy, Division of Chemical Sciences, Geosciences, and Biosciences, under Grant No. DE-FG02-03ER15391.