We report measurements of the degree of linear polarization of scattered light as a function of excitation frequency near the Doppler-broadened
NaD2 resonance line. For resonant excitation of the
D2 line, the hyperfine interaction strongly depolarizes the emitted light due to precession of the electronic angular momentum $\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}$ prior to spontaneous emission. However, as the laser frequency is tuned away from resonance, the polarization degree sharply rises to the level predicted using a simple
JMJ basis, i.e., neglecting any coupling of the electronic angular momentum $\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}$ with the nuclear spin $\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}$. Roughly speaking, there is a transition from
F selection rules ($\stackrel{\ensuremath{\rightarrow}}{\mathrm{F}}=\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}+\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}$) for resonant excitation to
J selection rules for off-resonant excitation. We present a rigorous calculation of the polarization degree with the use of multipole moments of the density matrix which agrees quantitatively with our data and also predicts complicated interference structure when Doppler broadening is negligible. We show that this structure may shift peaks observed in precision laser-spectroscopy experiments. For Doppler-broadened transitions we discuss a simplified approach (based on an approximation to the Voigt profile) which treats separately the contributions of resonant and off-resonant scattering.
A report is given of the first quantitative study of the spontaneous and stimulated electronic Raman scattering by a resonance doublet of the sodium atom excited resonantly at the D 1 and D 2 lines by a tunable dye laser. Theoretical and experimental analyses of the differential scattering cross section and polarization properties at the Stokes and anti-Stokes frequencies show that the observed scattering is due to a nearly resonant process involving the ground state 3 S 1/2 as the dominant intermediate state. The stimulated Stokes and anti-Stokes scattering lines, which are shifted from the D 1 and D 2 lines by an amount corresponding to the frequency separation between lowest-lying excited doublets 3 P 1/2 and 3 P 3/2 , are observed by exciting a sodium vapor cell with a passively mode-locked dye laser.
We investigated the near resonant scattering and collision induced fluorescence of sodium atoms with doublet excited states in a weak laser field. By changing the frequency of the incident light and measuring the integral intensities of the components of the scattered light, the near resonant excitation cross-section of each sublevel was obtained as functions of the frequency detuning. Their variations are qualitatively explained by the interaction potential between the sodium atom and various collisional perturbing species. We have measured the variation of the induced D1 and D2 fluorescence with laser power, density of sodium atoms and pressure of buffer gas. It is shown that the relation is linear. The experimental results are in agreement with the theory.
Sodium vapor, in the density range
1013 to 5 \ifmmode\times\else\texttimes\fi{}
1014 ${\mathrm{cm}}^{\ensuremath{-}3}$, was excited by a cw dye laser, tuned 20-150 GHz from either the
D1 or
D2 resonance line. We observed a three-peak scattered spectrum, consisting of the Rayleigh component at the laser frequency, and the two fluorescence components (direct and sensitized) at the atomic resonance-line frequencies. Corrections to the Rayleigh signals for anisotropy and polarization effects, and to the fluorescence signals for radiation trapping, were made in order to obtain the ratio of the sum of the total intensities of the two fluorescence components to that of the Rayleigh component. This ratio combined with a measurement of the line-wing absorption coefficient yields the sodium density and the
D-line self-broadening rate coefficients [${k}_{\mathrm{br}}=4.67\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$
cm3${\mathrm{s}}^{\ensuremath{-}1}$ (\ifmmode\pm\else\textpm\fi{}15%) for the
D2 line and ${k}_{\mathrm{br}}=3.07\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$
cm3${\mathrm{s}}^{\ensuremath{-}1}$ (\ifmmode\pm\else\textpm\fi{}15%) for the
D1 line]. Asymmetry in the self-broadened line wings due to fine-structure recoupling was observed. The measured intensity ratio of the
D lines, combined with pulsed measurements of the effective radiative decay rates in the presence of radiation trapping, yields the fine-structure collisional-mixing cross section [$\ensuremath{\sigma}(3{P}_{\frac{3}{2}}\ensuremath{\rightarrow}3{P}_{\frac{1}{2}})=172$
A˚2(\ifmmode\pm\else\textpm\fi{}18%)] at $T\ensuremath{\cong}300\ifmmode^\circ\else\textdegree\fi{}$ C. Our results are compared to other experiments and to theory.
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.