Influence Of Image Sensor's Nonlinear Response Characterization On Measurement Of Laser Beam Quality

Laser detection,laser communications,laser machining and other related fields of the domestic test instrument market provide more rigid demands: comprehensive,rapid and accurate evaluation on the performance of laser beam parameters.However,owing to the shortcoming of the nonlinear response characteristics of the image sensor,and it brings certain effects on the measurement of laser beam quality,and thus analyzing the influence of the nonlinear characteristics on laser beam quality,can effectively evaluate laser beam quality,improve the measuring accuracy of laser beam quality and lay the foundation in various fields of laser application.To begin with,the parameter description,beam quality assessment indicator and beam quality measuring principle of laser beam are studied in the paper.Due to the internal nonlinear optoelectronic response and noises factor of the image sensor,the main works of the paper are as follows: for one thing,in order to better reduce the noise effects of the image sensor and background noises,the spot image is carried on the process of denoising algorithm in the paper,making it possible to suppress the noise effectively.For another thing,the improved calibration method of the image sensor is proposed on the foundation of photoelectric response,and thus solving the existing problems where traditional calibration methods have the problems such as complicated experiments,limited sampling,narrowing the linear range and low utilization of gray value and so on.The method mentioned in the paper can improve the utilization of the grayscale of the image sensor,and can realize the work of fast,real-time and online linear grayscale calibration.Finally,selecting CCD photoelectric detector as the measuring element in the experiment,by setting up a laser beam quality measurement system experiment platform based on CCD,the experiment has verified the existence of the nonlinear response characteristic of the CCD.At the same time,the photoelectric response linear range of three different types of CCD can be obtained by statistical methods.On this basis,the influence of laser beam width,far field beam divergence as well as beam quality factor M2 is analyzed under four different wavelengths before and after calibration.The result of experiment and data shows that the nonlinear characteristics of the CCD can lead to the measurement of larger laser beam width and far-field divergence angle and laser beam quality factor M2,and it breeds some influence for the measurement of laser beam quality.By using the optoelectronic response character's calibration result of the CCD to make nonlinear gray level restoration on images,the laser beam quality factor M2 can be measured more accurately and the relative error can be decreased by 2.36% compared with the measuring result by the international standard laser beam profiler.The method mentioned in the paper can effectively increase the measuring accuracy of the laser beam quality factor M2 and it has great application values on evaluating the laser beam quality.