The total cross sections for inelastic collisions between sodium and inert gas atoms, leading to 3 2P1/2 ↔ 3 2P3/2 excitation transfer in sodium, have been determined in a series of sensitized fluorescence experiments with sodium – inert gas mixtures. The sodium vapor was maintained at a pressure of 5 × 10−7 mm Hg, at which there is no trapping of the resonance radiation, and the inert gas pressures ranged from 0 to 1 mm Hg. The cross sections Q1(3 2P1/2 → 3 2P3/2) and Q2(3 2P1/2 ← 3 2P3/2) are as follows: Na–He, 86.0 and 44.8 Å2; Na–Ne, 67.0 and 35.4 Å2; Na–Ar, 110 and 55.9 Å2; Na–Kr, 85.0 and 43.6 Å2; Na–Xe, 89.8 and 45.6 Å2. The ratios Q1/Q2 are in agreement with the value predicted from the principle of detailed balancing and the cross sections also agree, as to order of magnitude, with some theoretically predicted values.
Collision-enhanced Hanle resonances in the 3
2S1/2 electronic ground state of Na atoms have been studied in a phase-conjugate four-wave light-mixing geometry. Narrow resonances in zero magnetic field have been observed at very high inert-buffer-gas pressures, with a width of 21 mG, or less than 10 kHz, full width at half-maximum. The intensity and the width of these resonances has been studied as a function of buffer-gas pressure, of alkali-metal vapor pressure, of detuning from the
D1 and
D2 Na resonances, and of the intensity of the incident light beams. Saturation phenomena and power broadening are observed. The results are explained theoretically in terms of transversely pumped optical gratings. The equivalence of this description with collision-induced coherence gratings in the limit of low light intensities is demonstrated.