Digital controlled analog servo with auto-lock for atomic, molecular, and optical experiments.

High-performance servo systems play a crucial role in Pound-Drever-Hall (PDH) locking for ultra-stable lasers. Meanwhile, the timing sequence of cold atom experiments demands greater functionality and flexibility. To address this, we have developed a digital control high-performance analog servo based on field programmable gate arrays (FPGA), which combines the low noise and high bandwidth characteristics of traditional analog servo systems with the advanced capabilities of FPGAs, featuring an input noise of 4.9 μV. The FPGA-implemented automatic locking feature enables the PDH control loop to maintain its lock for prolonged periods in unattended environments. In addition, the dynamic hold functionality permits real-time synchronization with the timing of atomic experiments. We also conduct a detailed analysis of the digital noise introduced by the FPGA within the analog channel and propose a method to mitigate its impact by disabling the FPGA clock.