Phase and Frequency Coherent Multiple Pulse Spectroscopy: Applications to Collisional Dynamics

Abstract

Any two level system can be completely characterized once its resonance frequency w₀, Rabi frequency w₁, and relaxation times T₁ and T₂ are known. But two-level approximations break down in many real spectroscopic applications; for example, measurements of intermolecular interactions, energy transport, or collision rates usually require explicit consideration of many distinct coupled states. As a result, the information obtainable from absorption spectra or simple laser pulse sequences is often insufficient.We have been exploring the uses of laser pulse sequences with independently variable pulse phases, pulse frequencies, and pulse shapes to extract information from complex systems. In this paper we will consider only collisional effects in gases, and will show that dual frequency pump-probe experiments give for the first time an essentially complete description of the dynamics of translational energy redistribution from a non-equilibrium state.