Study Of Optical Crystal Nonlinear Measuring Method Based On Digital Image Processing

Sheik-Bahae introduced single-beam Z-scan technique for measuring the nonlinear characteristics of crystal in 1989. Because this technique has simple device and high sensitivity, it has been widely applied to research the nonlinear characteristics of crystal. In recent years, Z-scan technique has been developed on this basis, improved the sensitivity of measurement, and expanded the measuring content.In this paper, we use digital image processing technology to innovate the Z-scan technique. This innovation is different from purely improving the experimental optical transmission line or experimental conditions in the past. In this paper, we particular introduced the ideas, methods and steps of the innovative experiment. We also introduced how to get the digital image of the experiment and how to process the digital image. We compared the new method with the traditional method to prove the correctness and effectiveness of new methods. At the same time, we design a testing system based on the new method, including how to obtain the digital image and digital image processing two parts. The data processing is automatic.We are using the power meter to measure the corresponding laser power in traditional Z-scan experiment. In this paper, we use a CCD camera to get a group of digital images with the crystal samples at the different Z-axis locations. We use digital image processing technology to reduce the image noise, improving image quality. Then, we use the relationship between the gray of the digital image and the light intensity of the spot, obtain the energy distribution of the spot in Z-scan experiment. We can extract the information from the digital images, such as the energy distribution of the spot. With this method, we can not only instead of the using of power meter, but also we can get more other information. With this method, we can achieve the original function of Z-scan experiment, greatly simplify the complexity of the experiment, and can get more information than before. The most advantage of this method is we can do Z-scan experiment without aperture. Using the digital images, we can select appropriate facular area instead of the aperture. So, we can do only one Z-scan experiment and get a group of digital images. Then we select different sizes of facular area on digital images instead of different holes, we could get more information. This method has a broad application prospects, a lot of physics experiments could use a similar method to improve it.At last, we set up the original Z-scan experimental platform and the innovative Z-scan experimental platform to do the experiment. We compared the results of the two methods. We discussed the error sources of the innovative method. The measurement results proved that our innovative method is successful.