A Method on Laser Power Stabilization in Optical Detection Cesium Atomic Clock

Abstract

Laser detection avoid the limitation on cesium clocks’ lifespan due to electron multipliers. However, the laser inevitably induces light shift. By measuring the frequency shifts under various light powers, we study the light shift. The dependence of the light shift on the light power is 2 × 10⁻¹²/mW. The Allan deviation of the output power of the laser diode is 4.5 × 10⁻³ at 10⁵ s under free running. The temperature coefficient of the clock is 1 × 10⁻¹²/℃. For a high-performance cesium clock, the light shift is one of the main restricts to accuracy and long-term stability. In order to improve the clock’s long-term frequency stability, accuracy and temperature coefficient, we propose a method for laser power stabilization. This method uses a liquid crystal variable retarder to tune the polarization of the light, in order to feedback control the light power with respect to the photoelectric detector. We theoretically analyze the method, and find that the drift of light power mainly results from the temperature drift of electronic elements. The temperature drift is below 1 × 10⁻⁵/℃, manifesting the theoretical feasibility. We build an experimental system and measure the light power for 20 days. The stability of light power is 6 × 10⁻⁵ at 10 s, and 3 × 10⁻⁶ at 10⁵ s. Moreover, the temperature coefficient reduces to 2 × 10⁻¹³/℃ from 1 × 10⁻¹²/℃. Therefore, the method effectively improves the performance of the clock. Besides, it can be easily applied to other experiments that requires laser power stabilization.