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Journal of the Optical Society of America B

Improvement in the Sagnac-loop laser frequency stabilization

Taro Hasegawa

Published Dec 2, 2024• 1 citation
Publisher

Abstract

The laser frequency stability locked to the D 2 transition of 85 Rb at 780 nm using a Doppler-free Sagnac-loop stabilization scheme has been improved. In a previous work [ J. Opt. Soc. Am. B 40 , 667 ( 2023 ) JOBPDE 0740-3224 10.1364/JOSAB.482223 ], changes in birefringence at the absorption cell windows, influenced by the cell temperature, and in the rubidium vapor, affected by magnetic field fluctuations, significantly influenced the laser frequency stability. By aligning the polarization, the short-term stability (<10s) of the locked laser frequency was improved; however, the long-term stability remained unaffected. We attribute this long-term stability to temperature-induced changes in the optical path length of the wave plates. By removing the wave plates from the setup, the long-term stability has been successfully improved.

DOI
10.1364/josab.542410

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The laser frequency stability locked to the D 2 transition of 85 Rb at 780 nm using a Doppler-free Sagnac-loop stabilization scheme has been improved. In a previous work [ J. Opt. Soc. Am. B 40 , 667 ( 2023 ) JOBPDE 0740-3224 10.1364/JOSAB.482223 ], changes in birefringence at the absorption cell windows, influenced by the cell temperature, and in the rubidium vapor, affected by magnetic field fluctuations, significantly influenced the laser frequency stability. By aligning the polarization, the short-term stability (<10s) of the locked laser frequency was improved; however, the long-term stability remained unaffected. We attribute this long-term stability to temperature-induced changes in the optical path length of the wave plates. By removing the wave plates from the setup, the long-term stability has been successfully improved.
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A novel frequency stabilization method for external cavity diode lasers by using an all-pass polarization-split Sagnac loop is proposed. This scheme uses a quarter waveplate to convert the incident beam to a circularly polarized beam, and a polarization beam splitter for the input and output of the Sagnac loop. The two beams with perpendicular polarizations counter-propagate in the loop and experience different absorption of the Rb cell; therefore, the Sagnac loop output beam is converted into elliptical polarization. The dispersion phase shift induced by Rb saturation absorption can be obtained by balanced polarization-divided detection of the Sagnac loop output beam. The experimental results showed the feasibility and merits of the new method. This scheme is simple, robust, low-cost, and has potential applications in atomic physics experiments.