| As the length scale and the original reference of laser interferometry,the accuracy of laser wavelength?frequency?determines the highest relative measurement accuracy of interferometry system.Therefore,the study of laser frequency stabilization has been a hot issue in the field of precision and ultraprecision laser interferometer measurement.Especially in recent years,under the promotion of the rapid ultra-precision processing industry development such as MEMS manufacturing,microelectronics equipment,the next generation of laser interferometry technique and system integration will continuously direction to the wide range and ultra-precision.The relative measurement accuracy will be as high as 10-7 to 10-8,the frequency of the light source needs to improve the accuracy to 10-8 10-9,which lead the laser frequency stabilization technology into a new stage of development.Laser frequency stabilization of offset frequency locking method,as a new concept of laser frequency stabilization,is proposed in recent years.It organically combines the advantage of Iodine absorption spectrum whose optical frequency precision is Ultra-high.It is possible to be the ultra-high-precision laser frequency stabilization technology for the next generation of ultra-precision laser interferometer system.This paper,on the basis of the principle of offset frequency locking laser frequency stabilization which is deeply analyzed,aims at the problems which have influence to laser frequency stability in offset frequency locking frequency stabilization system,such as there is a greater frequency modulation of offset frequency signal,the thermal inertia of controlled object is too large to control,and the debugging control algorithm is complicated,I design and implement offset frequency signal detection unit,frequency stabilization digital controller and the corresponding frequency stabilization control algorithm in offset frequency locking laser frequency stabilization system.The main research topics are as follows:Firstly,this paper analyses the principle of offset frequency locking of laser frequency stabilization system and initially establish the frequency stabilization error model.It pointed out that although in theory the frequency stability in the offset frequency locking frequency stabilization laser could be greatly improved,in the actual system the offset frequency detection error,the value of offset frequency locking error,and other factors restrict the further improvement of laser frequency stability.Secondly,for the problems of the beat signal between iodine stabilized lasers and laser that need to be stabilized,such as the small amplitude,the large frequency range,the high-frequency noise,I design and implement detection and conditioning circuit for the beat signal with a high-gain and large bandwidth,Realize the beat signal high-precision extract and the effective amplification,and use the reduced frequency divider method convert it to the low frequency signal.Thirdly,for the problems of the beat signal,which are brought by the output frequency modulation of the Iodine frequency stabilization laser,such as sideband interference with various frequency components,the detection error of offset frequency value,proposing the methods of sideband frequency suppression and offset frequency value detection based on the techniques of Long threshold synchronous digital frequency measurement design and implement the corresponding module of high accuracy digital frequency measurement,complete the exact acquisition of offset frequency value with the effective suppression for the sideband frequency of modulated signal.Fourthly,a high accuracy digital controller,which is transplanted with ?C/OS real-time operating system and integrated with multi-task controller,is designed to fit the need of frequency stabilization system.The temperature of laser tube can be sampled with high accuracy.The state of laser can be identified effectively.The control volume can be exported and adjusted by power amplifier.The interface for control algorithm is also well tested.Finally,based on the characteristics of each unit,this paper established the thermal model of frequency stabilization system.Aiming at the large thermal inertia and delay of the laser being controlled,step response identification is used to get model coefficients,which are the proportional gain coefficient,thermal inertia coefficient and delay coefficient.A frequency stabilizing control algorithm is designed,which is based on the Smith-PI control algorithm.Based on the offset frequency locking signal measurement unit,digital controller and frequency stabilizing control algorithm,this paper established the laser frequency stabilizing system using offset frequency locking technology.According to the experiment result,the offset frequency achieves locking state after about 30 min preheating time.The error of offset frequency locking is less than ±500kHz.The relative frequency stabilization accuracy can get 10-9... |
PDF Full Text Request