Chinese Optics Letters, Volume. 20, Issue 7, 070201(2022)

Automatic, long-term frequency-stabilized lasers with sub-hertz linewidth and 10−16 frequency instability

Author Affiliations
• State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
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We report two ultra-stable laser systems automatically frequency-stabilized to two high-finesse optical cavities. By employing analog-digital hybrid proportional integral derivative (PID) controllers, we keep the merits of wide servo bandwidth and servo accuracy by using analog circuits for the PID controller, and, at the same time, we realize automatic laser frequency locking by introducing digital logic into the PID controller. The lasers can be automatically frequency-stabilized to their reference cavities, and it can be relocked in 0.3 s when interruption happens, i.e., blocking and unblocking the laser light. These automatic frequency-stabilized lasers are measured to have a frequency instability of $6×10-16$ at 1 s averaging time and a most probable linewidth of 0.3 Hz. The laser systems were tested for continuous operation over 11 days. Such ultra-stable laser systems in long-term robust operation will be beneficial to the applications of optical atomic clocks and precision measurement based on frequency-stabilized lasers.

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1. Introduction

Lasers with high-frequency stability and narrow linewidth are indispensable tools in optical atomic clocks[1,2], gravitational wave detection[3], low noise optical/microwave synthesis[4,5], tests of fundamental physics, and precision measurement[6,7]. Such lasers are usually achieved by locking the laser frequency to the resonance of ultra-stable Fabry–Pérot cavities with the Pound–Drever–Hall (PDH) technique[8]. To realize the aforementioned applications, many labs around the world have constructed ultra-stable lasers with frequency instabilities at the $10−16$ level[2,914]. Some have constructed lasers with frequency instabilities of $10−17$, which are stabilized to cryogenic cavities[15,16] or optical cavities at room temperature with a length larger than 35 cm[17] for lower cavity thermal noise[18]. While methods for further improving laser frequency stability and laser linewidth are explored[19,20], there is growing interest in making such frequency-stabilized laser systems transportable[12,13,2124], automated, robust, and suitable for practical applications[25,26].

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Chengzhi Yan, Haosen Shi, Yuan Yao, Hongfu Yu, Yanyi Jiang, Longsheng Ma. Automatic, long-term frequency-stabilized lasers with sub-hertz linewidth and 10−16 frequency instability[J]. Chinese Optics Letters, 2022, 20(7): 070201

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Category: Atomic and Molecular Optics