Laser frequency stabilization using HCN gas cell

Laser frequency fluctuations are one of the limiting factors for many laser-involved precision measurements such as interferometry. Laser frequency locks with the Pound-Drever-Hall (PDH) method use typically an optical cavity as a reference, which are very sensitive to environmental noises. In contrast, spectroscopy methods using atom or molecular transitions and phase modulation spectroscopy behave better in the long term. A well-sealed fiber-based Hydrogen Cyanide (HCN) gas cell that is very compact and light-weighted is chosen. And We investigate laser frequency stabilization using the absorption line of an HCN gas cell instead of a cavity to provide better frequency stability in the low-frequency regime. In our lab, a fiber-coupled HCN gas cell laser frequency lock was built and thermally stabilized to provide better long-term stability. It is designed to work with our heterodyne interferometer around 1550 nm wavelength. The HCN gas cell locking setup using phase modulation (PM) spectroscopy shows less than 0.5 MHz frequency drift over 12 hours measurement and stability levels of 1 kHz/^√Hz for frequencies above 0.2 Hz.