在冷原子干涉仪的研究中, 常采用三个拉曼光脉冲实现对原子束的相干操控(分束、反射和合束)。拉曼激光的功率抖动会引起Rabi频率的变化, 从而带来严重的干涉相移噪声。这些噪声对用于高精度转动加速度测量的冷原子干涉仪来说是不可忽略的系统噪声, 因此实现拉曼激光的功率稳定对于实现高精度原子干涉是至关重要的。采用声光调制器(AOM)作为执行器, 设计了一套用于稳定激光功率的数字控制系统。在对AOM进行系统辨识和控制器仿真设计的基础上, 利用Labview程序实现了激光功率稳定的PID控制。测试结果表明, 在测量时间为1 h情况下, 激光功率的不稳定度由系统闭环前的1.67%降低到了系统闭环后的0.19%, 极大地提高了干涉信号的稳定性, 同时也降低了系统噪声。

Three Raman pulses are usually adopted to make cold atomic beams to split, reflect and recombine when doing cold atom interferomertry experiments. The stability of Raman laser power is as important as frequency, because it causes the Rabi ratio to change with it. When the Rabi ratio changes, the final phase difference between the two separated atom beams changes as well. It is a great disturbance for interferomertry signal stability and also the signal to noise ratio. The effect is more than acceptable when it comes to atom interferometer used as high precision acceleration measurements. Keeping laser power stable can improve phase noise a great deal. Thus a digital control system was designed for higher laser power stability using an acousto-optical modulator(AOM) as a controller, and the feedbacks from the AOM were applied to compensate the power variation outside the cavity of a laser. After realizing the identification with the AOM and a simulation model for it based on the identification results, an PID controller was programmed in the Labview language. Experimental results show that the the laser power instability can be reduced from 0.19% to 1.67% with the method under the measurement time of 1 h. And it works really well for the cold atom interferometer system.