A digital control for the Ultra-Stable Laser system

We describe a digital control for the ultra-stable laser system. The digital automatic precision control consists of PDH locking loop and cavity temperature loop. The cavity temperature after temperature closed-loop control has been stabled around 293.65 K, and the standard deviation of temperature fluctuation is 0.13 mK based on 22 hours data. Frequency instability of the ultra-stable system is measured 2.66 × 10^-15@1 s after all the loop are locked, while the contribution of PDH photodetector and error signal generation circuit to frequency instability is around 7.1 × 10^-17 @1 s.