Phase Shift Extraction And Wave-front Reconstruction In Double Wavelength Phase-shifting Interferometry

Compared with traditional optical holography, digital holography avoids the inconvenienceof wet processing and the difficulty of repositioning for the original object image. Using moderndigital recording devices and computer image processing technology, the data and image can beoperated in many ways conveniently and accurately. It has been widely applied in many fieldssuch as scientific research, engineering technology and biomedicine. After phase-shifting methodwas introduced into the digital holography, it was called phase-shifting digital holography. Byusing phase-Shifting Interferometry, phase-shifting digital holography eliminated the zero orderterm and twin image existing in coaxial digital holography by simple calculation, solved theproblem caused by the off-axis requirements of digital holography and low resolution limit ofdigital recording medium, generalized the application of the technology, reduced the skillrequirement of the experiment setup and it’s adjustment, decreased the effects of errors, andautomatically removed the disturbance from the twin image and zero order item in traditionalholography.In research of phase-shifting digital holography algorithm, there are fixed steps algorithm,equivalent steps algorithm, and generalized phase-shifting algorithm. The fixed step algorithmneeds fixed phase shift value, the equivalent step algorithm requires that all the phase shift valuesare equal. For fixed and equivalent step algorithm, we need to calibration the phase shifter beforethe optical experiment and always the results will be affected by the precision of phase shift.Generalized phase shift algorithm can automatically extract phase shift values, remove thenecessity to calibrate the phase shifter before experiments, and eliminate the dependence on theprecision of phase shifter. So generalized phase shift algorithm has good prospects fordevelopment now. Among generalized phase shift algorithms, the two-step generalizedphase-shifting digital holography has many merits, including less number of interferograms and high precision. Introducing double wavelength or multiple wavelength algorithms in existingphase-shifting digital holography can expand the range of phase shift values and further promoteits application.This paper briefly introduces development and application of the digital holography andphase-shifting digital holography and expounds the basic principle of phase-shifting digitalholography, including principles, formulae, and algorithms for phase shifts extraction, wave-frontreconstruction, and automatically correction of wave-front reconstruction errors. To solve theproblems in phase shifts extraction and wave-front reconstruction for double wavelengthphase-shifting digital holography, the algorithms for phase shift extraction and wave-frontretrieval and the corresponding experiment setup designation with specific experiments areresearched. Based on the existing two-step generalized phase-shifting digital holographyalgorithms, two wavelength light sources are used to design new phase shifts extraction algorithm,where the extracted phase shift values can be doubled. A simple method is also suggested toautomatically correct the chromatic errors caused by crosstalk from different color images underthe requirement of sampling theorem. And more, the orthogonal light path to record reflectiveobjects and rectangular experiment light path for multi wavelength recording are designed. Theclear image of a Chinese coin is achieved by using the orthogonal light path experiment. In themulti wavelength experiments，red and green light sources and a resolution target are used toinvestigate the method here. The experiments results show that the two color images can befused together very well.