Experimental research of CCD/LCD in holography

Abstract

Holography has been widely applied in industry measurement, especially in 3D non-contact testing. Combining a high resolution charge-coupled device (CCD) with a phase modulating liquid crystal display (LCD), holographic interferogram recording and display could be realized by digital holographic technique. Digital holographic technique has a great number of important and practical applications. In the conventional holography hologram was detected and reconstructed by the holography panchromatic plate, or the photoconductive thermoplastic film, or the BSO crystal and etc. But in the digital holography--the numerical version of the conventional holographic technique, hologram is digitally detected by CCD and then displayed on the computer monitor. By reconstruction, the hologram is writted into LCD, then illuminating the LCD with the reference wave, the tested object may be reconstructed optically. In this paper the application technique of CCD/LCD in holography is theoretically studied and the bottle techniques have been solved. According to the resolving power of the CCD and LCD, the angle between the two interfering waves should be less than 3° for recording the interference fringes with high spatial frequency. The simple and prospective optical architecture is perhaps Twyman-Green interferometer for easy to adjust the required small angle between reference and tested object waves, and also optical path deference for satisfying the requirement of spatial and temporal coherence. The disadvantages of CCD/LCD digital holographic technique is the small separation angle between zero-order and ±1-order diffraction. In order to separate ±1-order from zero-order diffraction, the minimum fringe spacing formed by the interference of object wave with reference wave should satisfy the sampling theorem. This decides a relationship between the size of object and the recording distance, which will be discussed in detail in the following text. And also discussion about the experimental research of LCD in digital holography would be included in our paper.