Yizhuo Zhang

Comparison and verification of numerical reconstruction methods in digital holography

The expressions for the reconstructed field from the sample of the diffracted wave, which is produced by illuminating an object, are found by use of different diffraction integrals in the digital holography. The numerical reconstruction methods that truncate and sample this field are compared in overlapping quality, accuracy, pixel resolution, computation window, and speed. The fast Fourier transform (FFT)-based direct integration method for the Fresnel integral and the modified FFT-based direct integration method for the Rayleigh-Sommerfeld integral have similar overlapping quality and can flexibly control pixel resolution and computation window size. Meanwhile, the FFT-based angular spectrum method is superior to the FFT-based convolution method in accuracy and speed. The experimental results are presented to verify these consequences.

Measurement of temperature field in the region near to the radiator by using digital holography

A simple method for measurement of temperature field in the region near to the metal plate of the radiator is demonstrated by using digital holography in the Lensless Fourier transform configuration (LFT). The temperature is measured within the boundary layer of the convective flow field. The deviation of the temperature produced by this method, from that obtained by the thermocouple is rather small. It has shown that the method is reasonable and efficient.

Improvement of reconstruction algorithms in digital holography

Improved reconstruction algorithms based on the cyclical convolution are proposed. Comparing with traditional ones, the reconstruction pixel resolution and pixel quatity is fully controlled which is awfully required in real-time inspection of digital holography.

An improved reconstruction algorithm by direct discretization in digital holography

Digital holography combines the advantages of the optical holography and the digital image processing as a method for recording and reconstructing amplitude and phase of a wave field. Traditional reconstruction algorithms can only obtain image with the fixed pixel size. By directly discretizing the Reyleigh-Sommerfeld (RS) integral formula, a new reconstruction algorithm is proposed. Experiment result shows that the reconstruction pixel size and pixel number can be controlled with the proposed algorithm.