Measurement System Design And Experimental Research With High Accuracy For Laser Beam Quality

With the wide applications of lasers in many fields, how to detect and evaluate the laser beam quality effectively has become a key issue in the field of laser applications. Since the diffraction limit factor M2 factor was adopted in the 90's, it has become an effective and commonly used method to measure the laser beam quality, and how to quickly and efficiently measure M2 factor has also become a hot spot for researchers.This paper designed a high-precision laser beam quality measurement system which is based on the CMOS camera. The system used the image processing method to obtain the beam deflection angles, and then controlled the mirror to change the beam propagation direction by the electric device automatically, which can complete the adjustment of the optical path, so as to realize the beam vertically incident to the photosurface of the camera. On the basis, the system can realize the measurement of the M2 factor automatically. To be more specific, it mainly includes:Firstly, studied the existing evaluation method of the beam quality. Around the laser beam M2 factor, this paper developed the overall scheme of the laser beam quality measurement. Based on gravity method and second order moment method, this paper designed the image processing methods of calculating the laser spot center and size. According to the requirements of optical path adjustment during the process of beam quality measurement, this paper designed the optical path adjustment method with high precision based on image processing.Secondly, designed and completed the software and hardware of the laser beam quality measurement system and completed the joint debugging. Software included system settings module, stepper motor control module, parameter calculation module and image preprocessing module, and hardware included the system optical path module, the single-chip computer control module, image acquisition module, precisely electric fine-tuning device and its driver module and positioning module.Thirdly, with the developed laser beam quality measurement system, this paper completed a series of experiment. The results showed that:(1) this system could efficiently complete the light path adjustment, and with the adjustment, the beam deviation angle is less than the set deflection threshold 0.05 °;(2) different focal length lens had little influence on beam quality measurement;(3) measured and compared different wavelength, the results of this system and commercial systems ware basically identical, but the repeated accuracy was higher, and repeated measurement deviation could reach below 1.0%.