Hyperfine structures of Na $D_1$ transition line are investigated by using Doppler free high resolution polarization and saturation spectroscopies, and are compared with theoretical result which are calculated by considering a only single cycle of velocity selective optical pumping in a four level system.
The frequency and power stabilization, and continuous frequency scanning have been carried out for the cw dye laser which has the single mode obtained by inserting three solid etalons (0.22, 1.66, and 10mm in thickness) inside laser cavity. Its frequency has been stabilized by modulating the length of the reference cavity. which is a confocal Fabry-Perot interferometer of 375MHz free spectral range. Its long term frequency drift and the short term frequency stability are measured to be 70MHz/min. and 20MHz/min., respectively. And, its output power has also been stabilized by the feedback of the dye laser output power to the $Ar^+$ laser power supply. A stabilized single frequency can be scanned continuously in the full range of 3GHz by synchronously controlling both the laser cavity length and the angle of the intracavity etalon by IBM personal computer.
Absorption coefficients of the hyperfine structures Na $D_1$ line have been investigated for the cases, in which the pump beam and the probe beam have various polarization states, by using the saturation spectroscopy and these results are compared with theoretical results. The method that the absorption coefficients for orthogonal components can be measured simultaneously is proposed in the nonlinear medium induced by circularly or linearly polarized pump beam, and is compared with the saturation spectrometer and the velocity selective optical pumping spectrometer. This system are applied to high contrast transmission spectroscopy. The experimental results of this system agree well with the result of the saturation spectroscopy.
By the polarization spectroscopy, circular and linaer anisotropy are measured in Na $D_1$ line and compared with the theoretical results in detail. The birefringence due to the stress of the cell window has given the similar signals obtained by the velocity selective optical pumping spectroscopy. By using the dispersive signal, the dye laser frequency is locked to a Na atomic transition line ($3S_\frac{1}{2}$ , F=2 - $3P_\frac{1}{2}$ , F=2), and its frequency stability is measured to be 350kHz/hour in this case.
