Nonlinear parametric processes in gases under two-photon resonance and collisional relaxation

F. Horowitz, H.P. Grieneisen

Э. Г. Сапрыкин, Gennady I. Smirnov

The influence of isotropic depolarizing collisions on four-photon parametric processes is considered under resonance conditions. It is shown that, in particular, there is no parametric oscillation for J = 0→1 and 1→1 transitions between levels with total angular momenta J and waves with perpendicular linear polarizations if the line-up and orientation constants are equal. A study is made of the possibility of using resonance four-photon parametric processes in the determination of the relaxation constants of multipole moments of electron shells.

Н. Н. Рубцова, L. S. Vasilenko, Хворостов Евгений Борисович

Precise knowledge of collisional relaxation channels is in close relation with the research of both specific features of interaction potential and details of lineshape. When using nonlinear laser technique of spectral domain, it’s not so easy to distinguish between different channels of relaxation because of their integral contribution to the lineshape of rarefied gas. This report intends to demonstrate ability of coherent transient phenomena to overcome this difficulty. Comparative study of several photon echo modifications, performed in molecular gas SF6 has permitted to choose definite type of coherent transient phenomena, which is the most sensitive to peculiar channel of collisional relaxation. The data on relaxation rates of rotationally inelastic, elastic small angle scattering and depolarizing collisions in SF6 and its mixtures with buffer gases are examined.

Ye. V. Baklanov, Veniamin P. Chebotayev

M. S. Pindzola

Shaul Mukamel, A. Ben‐Reuven, Joshua Jortner

A theoretical study is presented of the effects of collisional perturbations on the time-resolved resonant and near-resonant photon scattering from a molecular system. The photon counting rate is formulated in terms of tetradic Green's functions in Liouville space. The collisional and radiative damping effects are handled by an effective-Liouvillian formalism. The formal expressions are disentangled by invoking a series of successive approximations, assuming short correlation times of the thermal bath, neglecting relaxation processes in the ground electronic state, considering rotational relaxation as providing the dominant damping mechanism in the excited electronic manifold, specializing to weak electromagnetic fields, neglecting some off-resonance processes and disregarding collision-induced radiative processes. The photon counting rate is expressed as a triple convolution of the photon counting rate for the free molecule with the Doppler Gaussian profile and with a Lorentz profile. The latter incorporates purely collisional effects due to intrastate cross relaxations and proper ${T}_{2}$ processes. The theory accounts well for the recent experimental data of Williams, Rousseau, and Dworetsky on collisionally perturbed ${\mathrm{I}}_{2}$ molecules.