High precision wavelength measurement system based on FP cavity and saturation absorption peaks

Alkali-metal atomic vapor cells are widely used in the precision measurement of magnetic field and inertial rotation. The performance of the atomic sensors is closely related to the partial and total pressures of the mixed gases in atomic vapor cells. The exact composition and quantity of the gas mixture inside the vapor cells can be deduced from the optical absorption spectra, while a high precision wavelength measurement is required. We build a homemade high precision wavelength measurement system which is based on the scanning Fabry-Perot cavity and the saturation absorption peaks. As the laser current is scanning, the interference pattern and the transmission light intensity are recorded synchronously. After scanning, the stride length of all sample points is sequentially calculated from their interference patterns by a dedicated computer program. Patterns of several cycles are averaged to suppress the white noise and improve the precision. Compared with the commercial wavelength meter, which usually has an accuracy of about 50 MHz, our wavelength measurement system can achieve a higher precision below 10 MHz.