Computerized Optical Processes For almost 30 years, the silver halide emulsion has been first choice as the recording medium for holography, speckle interferometry, speckle photography, moir´ and optical e filtering. Materials such as photoresist, photopolymers and thermoplastic film have also been in use. There are two main reasons for this success. In processes where diffraction is involved (as in holographic reconstruction), a transparency is needed. The other advantage of film is its superior resolution. Film has, however, one big disadvantage; it must undergo some kind of processing. | Optical Metrology. Kjell J. Gasvik Copyright 2002 John Wiley Sons Ltd. ISBN 0-470-84300-4 12 Computerized Optical Processes INTRODUCTION For almost 30 years the silver halide emulsion has been first choice as the recording medium for holography speckle interferometry speckle photography moire and optical filtering. Materials such as photoresist photopolymers and thermoplastic film have also been in use. There are two main reasons for this success. In processes where diffraction is involved as in holographic reconstruction a transparency is needed. The other advantage of film is its superior resolution. Film has however one big disadvantage it must undergo some kind of processing. This is time consuming and quite cumbersome especially in industrial applications. Electronic cameras vidicons were first used as a recording medium in holography at the beginning of the 1970s. In this technique called TV holography or ESPI electronic speckle pattern interferometry the interference fringe pattern is reconstructed electronically. At the beginning of the 1990s computerized reconstruction of the object wave was first demonstrated. This is however not a reconstruction in the ordinary sense but it has proven possible to calculate and display the reconstructed field in any plane by means of a computer. It must be remembered that the electronic camera target can never act as a diffracting element. The success of the CCD-camera computer combination has also prompted the development of speckle methods such as digital speckle photography DSP . The CCD camera has one additional disadvantage compared to silver halide films - its inferior resolution the size of a pixel element of a 1317 x 1035 pixel CCD camera target is i m. When used in DSP the size as of the speckles imaged onto the target must be greater than twice the pixel pitch p . 2p as 1 m kF where m is the camera lens magnification and F the aperture number see Equation . When applied to holography the .
