Research On Calibration Technology Of Direct Measurement Device For Laser System Output Characteristics

With the rapid development of laser technology,laser has been widely used in various fields.In the application of laser system,laser beam quality has become one of the most important parameters to measure the performance of laser system.For the small aperture laser system,the beam quality measurement method has been relatively mature,and the Shaker-Hartmann wavefront measurement method is commonly used.But for the large aperture laser system,there is a lack of effective means to measure the beam quality directly at the outlet.In order to solve this problem,we plan to develop a measuring system based on the principle of Shaker-Hartmann wavefront sensor and with separated lens array as the core,which can directly measure the beam quality at the exit of large aperture laser system.But there is an important problem in this measuring system,that is,zero calibration.Therefore,it is of great value to study the calibration technology of large aperture beam quality measurement system.Aiming at the measuring system of large caliber especially meter caliber,a method of scanning calibration of large caliber measuring system with small calibrating light source is proposed.According to the arrangement of lens array in the measurement system,a light splitting method is designed to obtain three light beams by using a small aperture parallel beam through the glued cubic prism group,covering the horizontal and vertical directions,so as to obtain the whole calibration light source.The influence of error on wavefront restoration under different scanning modes is analyzed and one-way scanning mode is selected.Two different error modes of calibration light source are analyzed.Through simulation,the error of calibration light source parallelism is less than 5μrad when the error accumulates in the scanning process,and the error of calibration light source parallelism is less than 0.5μrad when the laboratory scale verification system has a diameter of 127mm,and the actual meter level measurement system has a diameter of 1.27m.When the error is corrected by feedback but not accumulated,the error tolerance is larger and the residual is the main influencing factor.The indexes of parallelism error less than 10μrad and parallelism residual less than 1μrad are proposed for 127mm aperture system and 1.27m aperture system,and verified by experiments.Finally,after the measurement system is developed,the full aperture scanning calibration is carried out to obtain the zero calibration data.The hardware and software of the scanning mechanism in the calibration system are designed to realize the requirement of high precision scanning calibration.The closed-loop displacement control system is composed of a stepper motor and a high-precision magnetic grid displacement sensor,and the PID control algorithm is combined to ensure the high positioning accuracy during scanning calibration.The parallelism error and residual error are calculated by self-verification experiment of the parallelism residual of calibration light source.The results show that the parallelism error can be controlled within 10μrad and the parallelism residual can be controlled within 1μrad during scanning movement,which verifies the feasibility of the scheme proposed in this paper.