High-Resolution Saturation Spectroscopy of the Sodium<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>D</mml:mi></mml:math>Lines with a Pulsed Tunable Dye Laser

The sodium $D$ resonance lines have been studied in saturated absorption with a repetitively pulsed tunable dye laser. The hyperfine splitting of the $3^{2}S_{\frac{1}{2}}$ and $3^{2}P_{\frac{1}{2}}$ states of ${\mathrm{Na}}^{23}$ is resolved. Measurements with a delayed probe reveal a remanent hole burning in the velocity distributions of the two ground-state levels, caused by a velocity-selective optical pumping cycle. A time-resolved observation of the collisional-velocity thermalization in the presence of Ar buffer gas is reported.