Dye laser frequency locking to the hyperfine structure (3S1/2, F=2−3P1/2, F=2) of sodium D1 line by using polarization spectroscopy

The frequency of a single-mode dye laser is locked to a hyperfine structure of the sodium D1 line without modulating the laser frequency. The frequency locking method uses the error signal from a dispersion curve generated from the polarization spectroscopic output. The servo loop provides a frequency fluctuation less than ±0.3 MHz for more than 30 min.