Study On The Wavefront Coding Technique And Its Application In Measuring Crack Width

How to extend the depth of field is one of hot topics in the field of applied optics. In traditional optical systems, the usual approach to extend the depth of field is to reduce the relative aperture, but this will decrease luminous flux and resolution of the optical system, and finally have an effect on details of the image. Wavefront coding(WFC) is a novel technique emerging in the 1990s, and it is an intergraded imaging technology combining optical imaging and digital signal processing together. By placing a special-purpose optical phase mask in the exit puiple to encode the wavefront of the optical system , the immediate image of WFC system is invariant to the defocus distance. However, the clear sharp image can be restored by digital processing. The novel technique is an innovation of the present imaging technology. The technique is not only extending the depth of focus but also decreasing the cost and increasing the allowable error of the system. Base on studay about the WFC technique, the WFC system with the cubic phase plate is designed to measure the crack width and the preliminary experiment has been carried out.Some researches in this dissertation have been carried out as the following:The relationship between the spot diagram characteristics of WFC em with the cubic phase plate and the optical system parameters are analyzed, and asymptotic expressions are given to describe these characteristics. By doing this, it is helpful to understand the design and essence of the WFC system.Based on the optical design software ZEMAX, the measuring system for crack width with the cubic phase plate has been designed and immediate images are restored. The assembly allowable errors of the measuring system are also analyzed.The measuring system for crack width with the cubic phase plate is constructed and many experiments are carried out. And then immediate images are restored.