Yongzhao Du

Spatial carrier phase-shifting algorithm based on principal component analysis method

A non-iterative spatial phase-shifting algorithm based on principal component analysis (PCA) is proposed to directly extract the phase from only a single spatial carrier interferogram. Firstly, we compose a set of phase-shifted fringe patterns from the original spatial carrier interferogram shifting by one pixel their starting position. Secondly, two uncorrelated quadrature signals that correspond to the first and second principal components are extracted from the phase-shifted interferograms by the PCA algorithm. Then, the modulating phase is calculated from the arctangent function of the two quadrature signals. Meanwhile, the main factors that may influence the performance of the proposed method are analyzed and discussed, such as the level of random noise, the carrier-frequency values and the angle of carrier-frequency of fringe pattern. Numerical simulations and experiments are given to demonstrate the performance of the proposed method and the results show that the proposed method is fast, effectively and accurate. The proposed method can be used to on-line detection fields of dynamic or moving objects.

Circular common-path point diffraction interferometer

A simple and compact point-diffraction interferometer with circular common-path geometry configuration is developed. The interferometer is constructed by a beam-splitter, two reflection mirrors, and a telescope system composed by two lenses. The signal and reference waves travel along the same path. Furthermore, an opaque mask containing a reference pinhole and a test object holder or test window is positioned in the common focal plane of the telescope system. The object wave is divided into two beams that take opposite paths along the interferometer. The reference wave is filtered by the reference pinhole, while the signal wave is transmitted through the object holder. The reference and signal waves are combined again in the beam-splitter and their interference is imaged in the CCD. The new design is compact, vibration insensitive, and suitable for the measurement of moving objects or dynamic processes.

Application of Wavelet Digital Filter in the Radial Shearing Interferometry

For the problem of spectrum aliasing of radial shearing interference fringes, a new technique for removing the background components and high frequency components of interference fringes based on discrete wavelet transform (DWT) is established. This image pre-filtering stage not only enables the FFT method to demodulate interference fringes with larger bandwidths but also reduces speckle noise significantly. When the wavefront is complex, the reconstruction RMS error is better than /25 by FFT method, however, by using the new method suggested here it is better than /40. Comparison analysis showed that the new method has strong capabilities to anti-noise and anti-aliasing of spectrum, reduces the frequency domain filter design requirements and improves the accuracy and stability of the wavefront detection.