Study On Digital Holographic Detection And Its Control System

Digital holographic detection is an important method of the laser nondestructive testing technology. It uses digital way to realize the record, storage and reproduce. In the domain of the nondestructive testing such as contour measurement, micro-circuit detection, micro particle detection, stress testing, observation of biological cells, deformation and vibration measurement, recording moving objects state and nondestructive testing component defects, digital holographic detection technology can give full play to their characteristics and advantages, which has a broad prospect.Real-time, highly efficient are essential features of the digital holographic detection. With the rapid development and popularization of the computer, CCD, digital image processing and automatic control technologies, digital holographic detection technology is also developing toward intellectualized and automated measurement. In view of the development trend of the digital holographic detection system, a set of automatic digital holographic testing control system has been designed in the thesis, which is applicable to the common digital holographic detection. This system can improve the efficiency of the research and development as well as shorten the cycle of the research and development. At the same time, it is helpful to debugging the system. Furthermore, the system will reduce costs and improve reliability, and it will bring a lot of convenience in engineering practice.Digital holographic detection system needs to control many areas. It is very difficult to make these parts united and coordinated. In this paper, three sub-control systems of the digital holographic detection have been designed and corresponding hardware and software modules have also been exploited. Moreover, all of designed sub-control systems can work conformably. It realized the phase-shift system based on the liquid crystal spatial light modulator. Since there are many encoding modes displaved on the LCD in the phase-shift system, we discussed the choices of the common encoding methods and verified the feasibility of using LCD as the phase-shift device. The CCD control software is developed by VC++, which can implement digital acquisition system automatically. An electronic control of the SCM and the stepper motor has also been developed, and design and use methods of hardwares and softwares have been described. The electric-control turntable system is realized by controlling the stepper motor speed, stepping angle and rotation direction.According to the developed digital holographic detection control system, a three-dimensional profile detection system with reflected mini-object has been established. The system uses liquid crystal spatial light modulator to introduce phase-shift in the reference light and rotates the illuminating object light to realize the surface measurement of the three-dimensional object. The sensitivity of the detection system is determined by the initial incidence angle and the small tilt angle of the illuminating object light. The three-dimensional profile information can be obtained by the phase-change before and after rotating object light directly. As for reflection measurement system, the result will inevitably be impacted by speckle noise. Using phase-shift introduced in reference light, data compression and smoothing filter processing methods can restrain noise to gain a better three-dimensional shape test results.Based on the optical zoom system, a real-time stress field detection system of the transparent materials in the process of loading has been constructed. The system will use optical zoom system to image the detected objects on the CCD, and then interfere with the reference light to form a hologram. A filter is used to filter the spectrum of the hologram images at different moments, and isolate the spectrum of object light. Through the inverse Fourier Transform, the images of light intensity can be obtained to detect real-time digital holographic, namely the stripe image with deformation information. The entire dynamic evolution process of the transparent material damage can be observed by the stripe image. When the stripe images are quantitatively analyzed, the stress field of the transparent material in the process of loading has been real-time detected.The digital holographic control system developed in this paper can also be used for other related optical systems. The digital lithography system based on DMD is a good example. Firstly, the three-dimensional mode of the tiny device to be processed can be designed by 3ds max or OpenGL. Then the section of the three-dimensional model will be displayed on DMD in sequence. And then a beam of parallel light will illuminate the DMD as certain angle. The order+1 light reflected by the DMD will act on the recording material through the optical zoom system. Using computer to precisely control the location of the electric-control lift table and the display time of sections on DMD, we will achieve the tiny devices lithography processing.In summary, a set of automatic digital holographic detection control system will promote the development of digital holographic detection and its control system. Furthermore, this system will lay certain foundation for the market of the digital holographic detection system.