Design And Realization Of Variable Optical Path Length Multi-pass Cell System

Infrared laser gas absorption detection technology is widely used in many fields such as environment,safety,medical treatment,etc.This type of technology is often combined with Multi-pass Cell(MPC)to meet gas detection sensitivity requirements.However,different concentrations of gas have different requirements for detection sensitivity.To meet the requirements for different detection sensitivity,MPCs are often required to adjust the optical path.On the other hand,the variable optical path design of the MPC is of great value for studying the noise in the cell,exploring noise compensation methods,and further improving the gas detection performance.First of all,the thesis proposes an easy-to-implement variable optical path MPC design method based on the basic principle of the Herriott-type MPC.The expression of the optical path expressed by the distance between the mirrors is given,which makes the optical path controllable.By controlling the angle of incidence,the spots are arranged in a circle on the concave mirror,and a method of adjusting the distance between the mirrors and the position of the exit point is proposed to realize the continuous and controllable number of reflections(integer).Using TracePro to perform optical simulation on the model to verify the feasibility of the method.Then,according to the parameters,the three-dimensional structure design,processing and assembly debugging of the MPC are carried out.The mechanical design of the MPC is mainly designed around the variable distance between the two concave mirrors,while meeting the requirements of sealing,integration,miniaturization,combined with actual needs and processing accuracy,the principle of variable structure is explained,and the structure is assembled in the MPC.After completion,the actual light path was debugged to verify the practicability of the MPC.Finally,in order to realize the gas environment control in the variable cavity length MPC,an environment temperature and pressure control system was built.Through MATLAB analysis and comparison,select more suitable and stable control algorithms,design related peripheral circuits and expert PID control algorithms,and control the temperature in the gas cell more quickly and accurately.Experiments have shown that the control temperature can be stabilized at±0.025℃ of the set value.Designing and building pressure monitoring related equipment,extracting gas from the inside of the gas cell and testing the tightness,testing pressure monitoring device.The experiment proves that the gas circuit has good air tightness and can reach the set pressure value.