Photon Echo Polarization Measurements in SF6 and SiF4

W.M. Gutman, C. V. Heer

Robert J. Nordstrom, W.M. Gutman, C. V. Heer

J. Meckley, C. V. Heer

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

Collisional relaxation in SF6 gas and its mixtures with He and Xe is studied by photon echo and stimulated photon echo methods from the standpoint of the possibility of identifying the contributions of different types of collisions. The nonexponential nature of the kinetic curve of the photon echo is clearly observed for pure SF6, it is weaker in the mixture SF6+Xe, and it is virtually completely absent for high degrees of dilution of SF6 with helium. These features can be explained on the basis of estimates, made from experimental data, of the critical delay between the exciting pulses (for which the nonexponential behavior should be most strongly manifested). In pure SF6 it is possible to distinguish the contribution of the inelastic channel (rotational relaxation) and the contribution of weak collisions. To distinguish successfully the relaxation channels in mixtures with buffer gases a heavier buffer gas and a much better time resolution must be used. It is shown that data obtained on the orientation and alignment relaxation rates by the stimulated photon echo method can serve as an upper limit for the rates of inelastic processes which cannot be measured by the photon echo method. The combined use of photon echo and stimulated photon echo methods made it possible to obtain data on the cross sections for elastic and inelastic scattering of the collisional pairs SF6–SF6, SF6–Xe, and SF6–He.

William Gutman

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

The method of a stimulated photon echo with specially selected linear polarizations of pumping pulses of a coherent resonant radiation is applied to a research of depolarizing collisions in molecular gas SF6 and its mixtures with buffer gases He and Xe. For the first time in one experiment the rates of a collisional decay of three lowest moments of polarization (population, orientation and alignment) are defined in an ensemble of gas particles. These rates of a relaxation are measured as functions on longitudinal velocities of resonant particles. In the frames of an experimental accuracy any noticeable dependence on velocities of particles was not detected both for orientation and alignment neither in pure resonant gas SF6 nor in mixtures. This result confirms the standard theoretical approach to depolarizing collisions. In pure SF6 decay rates of orientation and alignment have proved lesser than relaxation rate constant due to velocity changing (elastic) collisions. It means, that only the part of elastic collisions participates in destruction of multipole polarization moments of resonant levels. In comparison with our previous work the evidence is obtained that the relaxation of multipole moments seems to be j-dependent one in a medium of molecular gas SF6.