The depolarisation of the redistributed Na D1 and D2 line fluorescence caused by Na-Ar collisions after far-wing excitation was investigated. In the limit of zero Ar density the J=1/2 orientation and J=3/2 alignment reflect the distribution among Zeeman sublevels of Na 32PJ produced after absorption of a photon into one or several excited Na-Ar molecular states at small internuclear separation, followed by a mixing between these states during dissociation. Measurements of these quantities as functions of the detuning up to Delta omega J=50 cm-1 in the red wings are compared with quantum-mechanical coupled-channel (CC) calculations using realistic molecular potentials and thermal averaging, and with predictions from the factorisation approximation (FA) of the theory of redistribution. Fair agreement with CC calculations and FA predictions was obtained within the impact region, proving the validity of the factorisation assumption there. Outside this region the overall depolarisation is primarily due to reorientation of the Na 3P electronic angular momentum and is reproduced qualitatively by the CC calculations but not by the FA theory. Additional depolarisation connected with the fine-structure coupling was observed.

We have investigated experimentally and theoretically the spectral distribution and collisional depolarization of laser light near resonant to the Na transition 3 2S1/2~---,3 2P3/2 scattered from a Na/Ar mixture in a cell (nNa ~ 4.0 x 101 o cm 3, nAr ~ 1.0 X 1017 cm-3). In particular, at excitation intensity of ~3mW/mm 2 and bandwidth of <10MHz, intensity I F and linear polarization degree P~ of the D2-fluorescence component of the scattered spectrum have been measured as functions of the laser detuning A2 L from the D2-resonance within two regions: 1) I A 2LI < Doppler-width; 2) 20 > I A 2c[/A/l o > 1. Within the first region the influence of hyperfine splitting as well as pumping of the hyperfine and Zeeman sublevels of 3 2S1/2 was studied in detail. Using an overall, total collision cross section for depolarization of 3 2P3/2 state atoms, calculations on the basis of the theory of redistribution reproduce qualitatively, but in a consistent manner, the experimental functions lr(A 2i.) and Pp(A2L). The possibility to derive differential cross sections from Pv(A2L) is discussed.

Redistribution and depolarisation of light scattered by atoms undergoing collisions outside the impact region of the line profile has been studied experimentally and theoretically. In a cell experiment intensity and linear degree of polarisation of the fluorescence components 32S1/2 to or from 32P1/2,3/2 of Na atoms induced by collisions with Ar buffer gas atoms were measured as functions of the laser frequency omega L. The decrease of polarisation of the D2 component observed when omega L is shifted away from the D2 toward D1 resonance disagrees with calculations on the basis of the factorisation approximation of the theory of redistribution. Using Baylis (1975) potentials for the Na/Ar system, the effect is interpreted in terms of adiabatic coupling of the 32P3/2 electronic angular momentum to the collision axis during 'strong' collisions, giving rise to a greater than average depolarisation.

We have investigated experimentally and theoretically the change in the polarization state of polarized laser light scattered near a 2P3/2~2Sl/2 atomic resonance as function of the laser frequency. For a collision free Na vapor at number densities < 101~ 3 it is found experimentally, that the polarization degree changes from a small level at frequencies between hyperfine components of the 3 2P3/2*--,3 2S~/2 transition towards high values at separations large compared to the hyperfine splitting. By comparison with scattering theory it is shown, that this change is typical for the transition from resonant to nonresonant scattering in the presence of atomic hyperfine interaction.

The intensity and polarization state of the NaD