DETECTION AND INTERPRETATION OF COLLISIONAL TRANSFER AND ROTATIONAL ANISOTROPY FINGERPRINTS IN RESONANT FOUR-WAVE MIXING SPECTRA

Abstract

Coherent responses produced by resonant four-wave mixing (RFWM) in a weakly absorbing medium carry valuable information on the intrinsic properties and dynamics of the quantum states involved. Here, two aspects of RFWM applications are highlighted. \ First, the Two-Color (TC) version of RFWM was found to be a unique spectroscopic tool to directly trace collisional state-to-state transfer in isotropic gaseous media, both in the frequency% , 271 (1997).} and time, 3911 \ (2007).} domains. Second, the RFWM techniques appeared to be very useful for studies of the rotational anisotropy, 6314 (1997).}. Here we report new experimental one-color RFWM spectra of the OH radicals produced by laser photolysis of H$_{2}$O$_{2}$ at 266 nm. Polarization dependence and Doppler line structure of the spectra show clear evidence of the pronounced anisotropy of angular momentum (\textbf{j}) and velocity (% \textbf{v}) distributions as well as on the \textbf{j-v} correlation. The obtained results directly point to the pronounced OH helicity (i.e. \textbf{j% }$\parallel $\textbf{v}) which yet remained beyound the reach of purely optical means. For all mentioned cases, the line-shape theory, 010701 (2000).} is an optimal tool to derive compact expressions for the RFWM signals. The work was supported by the Swiss Federal Office of Energy, the Swiss National Science Foundation (200020\_124542/1), and by the Russian Foundation for Basic Research, grants 11-02-01296 and 11-03-00448.