One-thousandth-level laser power stabilization based on optical feedback from a well-designed high-split-ratio and nonpolarized beam splitter.

Laser power stabilization plays a significant role in atomic and molecular physics, quantum precision measurement, and optical sensing and measurement. In the classical method of using a feedback control loop to stabilize the laser power, the beam splitter is the conjunction element to connect the feedback beam inside the loop and the output beam outside the loop. The stability of its split ratio will directly affect the result of power stabilization, especially in demand of high split ratios for high-efficiency output. For the compatibility of a high split ratio and high stability in a power-stabilized system, we designed and manufactured a high-split-ratio nonpolarized plate beam splitter, whose split ratio was insensitive to variations of beam intensity, polarization, and ambient temperature. Based on the optical feedback of the designed beam splitter, the light intensity was closed-loop controlled by an acousto-optic modulator; finally, the power outside the loop was stabilized as well. The output power was stabilized at 537 mW and a 6 h long-term test was performed. The relative stability of laser power outside the loop in terms of root mean square and peak to peak was 2.72×10-4 and 1.60×10-3, respectively. The relative Allan standard deviation reached 2.78×10-5 at an average time of 200 s. These results will greatly benefit many practical fields that require laser power stabilization with high split ratios and one-thousandth-level stability.