Diffusion processes and atomic collisions of Na-He and Na-Ar systems have been studied by measurement of the time development of population gratings (Laser-Induced Population Grating; LIPG) induced in atomic levels by two intersecting resonant laser pulses and monitored through the Bragg diffraction of a probe laser beam. The diffusion process in the systems was observed through the decay of the LIPGs in the sodium ground-state (32S 1 2) sublevels. The pressure dependence of the diffusion constants were measured. The values showed rough agreement with the previously reported values which had been measured indirectly by the optical-pumping method. The gaussian process model and a simple collision kernel model were considered for the diffusion process. It was also found that with increasing buffer-gas pressure, the population gratings in the excited state 3 2P 1 2 were transferred to 3 2P 1 2, which was interpreted as an effect of fine-structure state-changing collisions.
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