Analysis And Experimental Research Of The Digital Holographic Microscopy

Digital holographic microscopy is one of applications of digital holography. Its progress follows with the progress made in digital holography technique. The idea of digital holography was first proposed by Goodman and Laurence in 1960s. But this technique was not feasible during that period because of restriction of computer technology and numerical recording materials. With emergence of high quality CCD and development of computer technology, digital holography stepped into a period with rapid progress in late 1990s. At present, digital holography is widely used in various microscopic domains such as biological cell observation, microcircuit inspection, granularity analyses and so on.Based on the theoretic analysis and experimental research, this paper deals with many primary problems of digital holography:(l) the theory of recording and reconstruction; (2) the separation condition of reconstructed images in off-axis digital holography setup; (3) the properties of recording and reconstructing in lensless Fourier digital holography. Meanwhile, the requirements of spatial resolution of recording medium about three kinds of holographic recording setups are compared. How to improve the resolution and the quality of reconstruction is the kernel of the whole paper. The methods to complete the microscopic measurements with digital holography are proposed after considering the current condition of my laboratory. The corresponding experimental results show: the resolution of our recording setup approaches μ m, which is close to the international coequal level. In this paper, the main innovative ideas are as following:1. By using the theories of Fresnel diffraction and holography, theoretical analysis and experiment of the recording and reconstructing of premagnification and phase-shifting in-line lensless Fourier digital holography are illuminated. The results show: the separation problem of three reconstructed images in reconstructing plane can be solved effectively with phase-shifting technique. Microscopic object can be magnified conveniently by lens in premagnification technique. And lensless Fourier holography can not only reduce the samplingrequirement in recording but also record higher frequency information of object than other methods. Thus, integrating the three techniques into the digital holography is an effective method to improve the resolution in the current condition where the resolution of digital holography is restricted by the performance of CCD. Meanwhile, the results will provide important references to achieve reconstruction with high quality in digital holographic microscopy.2. The numerical correction technique is proposed. It uses chirp function as correction factor to correct the blurred images introduced by imprecise mechanical adjustment. Its results show that through changing the three correction parameters in x, y and z directions, the quality of the reconstructed image is improved greatly.3. Utilizing both the numerical correction technique and premagnificationt technology, digital holography can be used in cell observation (including living cell) successfully. Its results show: the profile of cells in reconstruction plane is clear, the quality of reconstructed images is good and the resolution of reconstruction is high. It is testified that there is huge potential of the metrological applications using digital holography in micromeasurements.