In-Line Phase-Shifting Digital Holography

In digital holography, the off-axis setup can't make effective use of the pixels of a CCD camera because of the necessity for carrier fringe. And the size of the reconstructed image is also limited by the presence of zero-order and conjugate image in off-axis digital holography. In contrast, an in-line setup is free from such limitations and can realize accurate characterization of micro-scale objects. And the interactive influence of the coaxial diffraction wave components during reconstruction can be eliminated completely by phase-shifting method. This in-line phase-shifting digital holography has been applied to three dimensional microscopy, non-contact measurement, pattern recognition and surface contouring. This paper is concentrated on theoretical, simulating and experimental studies on the in-line phase-shifting digital holography. The whole paper is divided into four chapters.Chapter 1: The history and development of digital holography are reviewed, and the main applications are summarized. In addition, the main contents of the thesis are explained, and our research results in the field are given.Chapter 2: At first, the fundamental theory of in-line digital holography is given in detail. Second, some algorithms of elimination of the conjugate image and the zero-order image are introduced and summarized. At the end of this chapter, the experimental setup of in-line phase-shifting digital holography is described. Chapter3: Digital holographic recording and numerically reconstructing process is interpreted as a coherent optical imaging system. A mathematical model based on Fourier optics is developed to analyze the digital recording mechanism and properties of the in-line phase-shifting digital holographic system in comparison with those of the commonly used off-axis arrangement. Theoretical analysis demonstrate that in-line configuration is advantageous inenhancing the system performance. And the point spread function (PSF) of inline phase-shifting digital holography is calculated. Based on the PSF, some basic characters including reconstructed image lateral resolution and the size limit of the recorded object in the in-line phase-shifting digital holography are theoretically discussed. It is pointed out that the image resolution is in proportion to the size of the CCD chip and in inverse proportion to the recording distance. And it is also showed that the maximum size of the reconstructed image is determined by the size of a pixel and the recording distance. The influence of the fill factor of the CCD pixels on the PSF is simulated and the result show that the larger the fill factor of the CCD pixels is the wider the half width of the PSF is. Finally, an experimental result of in-line phase-shifting lensless Fourier transform holography is given.Chapter 4: The influence of different phase-shifting angle of reference wave in recording, of the phase-shifting error and of the quantization error on the quality of the reconstructed image is investigated respectively in two-step phase-shifting inline digital holography. And an effective method of eliminating the phase-shifting error is presented, in which the summation of the intensity bit errors of the reconstructed image is taken as an evaluation function for an iterative algorithm to find the exact phase-shifting value. The feasibility of this method is demonstrated by computer simulation. Then the optimal choice of the phase-shifting values of reference wave is done by computer simulation. The simulation results show that the reconstructed image noise is weak when the phase is in a certain range. At last, by numerical simulation to the effect of the quantization, it is found that the quantization noise is so low that it may be omitted when the signal is quantized more than 8 bit.