Sub-megahertz laser stabilization by harnessing orthogonality between the acousto-optic modulator dither and atomic spectroscopy

A sub-MHz frequency stability of the laser is crucial in the quantum-atom experiment where precise atomic transition is required for control and manipulation of atom like in the atom quantum computing. In this work, we have built the frequency stabilization system for the lasers used in our cold Rubidium atom experiment in the magneto-optical trap (MOT) and the optical tweezers. We utilized a Rubidium vapour glass cell as a frequency reference, which provides atomically absolute reference point with low complexity setup. By mean of the absorption of the laser beam by the Rubidium vapour, the saturated absorption spectroscopy (SAS) experiment was setup to produce the D2 line spectra. The acousto-optic modulator (AOM) was used to sinusoidally dither the laser frequency and consequently the resonance peaks in the spectra. Detailing in this work, the AOM sinusoidal dithering and the dithered SAS signal had orthogonality and were processed together to produce the error signal used to stabilize the laser frequency to the resonant peak. This frequency stabilization system achieved the frequency standard deviation below 0.80 MHz over up to 8 min 00 period. The system also allowed for stabilized frequency tunability over a range of 55 - 60 MHz about the target resonance peak. This performance is significant for stabilizing the lasers in the MOT experiment and related quantum-atom research.