Large Cavity Long Wavelength Tuning Interference Test Technology Research

With the development of science and technology, the aperture of optical system in modern times is becoming larger and larger. As a testing instrument of optical parts with large diameter, the wave length-tuned interferometer plays a crucial role. In addition, because some components need to be tested in Brewster angle, wavelength-tuned interferometer with long cavity is required. However, with large cavity length, some problems appear such as lack of wavelength resolution, residual vibration, etc. These problems bring phase-shifting error, which affects the accuracy and precision of the testing result. In this dissertation, a research has been made in order to resolve these problems.For the problem of insufficient wavelength resolution, low noise stabilized voltage supply with high precision has been made, and the wavelength resolution has been improved.Due to the large cavity length, the interferometer is more sensitive to the residual vibration. For this problem, a general method for reducing the influence of vibrations in phase-shifting interferometry has been researched to correct the surface phase map through a spectral analysis of a "phase-error pattern," a plot of the interference intensity versus the measured phase, for each phase-shifted image. The method is computationally fast, and is applicable to any phase-shifting algorithm. Over a 10×reduction in vibrationally induced surface distortion is achieved.At the same time, an advanced random phase-shifting algorithm to extract phase distributions from randomly phase-shifted interferograms has been researched to resolve the phase-shifting error problem. The algorithm is based on a least-square iterative procedure, but it copes with the limitation of the existing iterative algorithms by separating a frame-to-frame iteration from a pixel-to-pixel iteration. The algorithm provides stable convergence and accurate phase extraction with as few as three interferograms, even when the phase shifts are completely random. The algorithm is simple, fast, and fully automatic, and it effectively resolves the phase-shifting error problem.