Research On Digital Control System In Laser Frequency Stabilization

Laser frequency stabilization technology is a technology aimed at reducing laser frequency fluctuations.In the fields of metrology,atomic and molecular physics,and quantum optics,a stable laser frequency is crucial for accurate measurements.Since the1970 s,laser frequency stabilization technology has been extensively researched and applied.Among them,the PDH frequency stabilization technology is one of the most important methods.PDH frequency stabilization technology utilizes a Fabry-Perot cavity as a reference for comparing the laser frequency,thereby achieving precise frequency stabilization.In the locking process of PDH frequency stabilization experiments,analog control has disadvantages such as difficult parameter adjustment,information distortion during transmission,and limited flexibility.Digital control,on the other hand,offers greater flexibility and information robustness compared to analog control.Due to its superior performance and ease of implementation,digital control has become the preferred method in most modern optical experiments.Therefore,this paper focuses on studying an FPGA-based digital control system to enhance stability and operational flexibility in the locking process.This system can be applied to cuttingedge technologies such as precise quantum sensing and quantum state preparation.Furthermore,the development of laser frequency stabilization technology contributes to the advancement of various scientific and technological fields.This thesis will primarily focus on the following topics:1.We first conducted experiments on digital locking technology using Red-Pitaya and introduced the PDH frequency stabilization technique.However,during the PDH frequency stabilization experiments with Red-Pitaya,it was discovered that the limited output voltage range of ±1V resulted in frequent loss of lock,rendering it unable to meet the experimental requirements.To compensate for the limitations of Red-Pitaya,we decided to design alternative digital control systems for laser frequency stabilization experiments.Subsequently,we developed a digital controller for laser frequency stabilization systems based on NI’s PXI-7852 R board.The hardware and software components of the PXI-7852 R board and the fundamental principles of the controller are described.We then presented two methods for measuring system response and outlined the steps for lock-in and optimization of PID parameters using the PXI-7852 R board-based digital control system.The PXI-7852 R board offers an economical,efficient,and flexible solution for laser frequency stabilization.2.During the experiment,it was found that the control loop of the pattern cleaner introduced a significant amount of noise in the audio frequency range.By analyzing the main sources of noise through experiments,a feedback control theoretical model was established.Based on the Nyquist stability criterion and in combination with the critical gain margin method,an optimal parameter tuning of the control loop was achieved by implementing a digital control system based on the PXI-7852 R board.This resulted in a 30 d B increase in the gain magnitude of the feedback control loop,effectively suppressing the audio noise introduced by the pattern cleaner control loop.This provides a fundamental means of analysis for the application of the pattern cleaner in precision measurements.