Digital Holographic Microscopy And Study On The Several Application Technologies

Digital holographic microscopy is a new kind of microscopy that combined with digital holography and microscopy. The electronic device such as CCD or CMOS are used to recording the digital hologram, then the amplitude and phase distribution of the object wave can be reconstructed by numerical simulation of the diffractive processDigital holographic microscopy is a method of "optical recording, numerical reconstruction" to recover complex amplitude of the object wave, it is a technology with characteristics of no destruct to the sample, high resolution, fast speed, etc. Because of these advantages, digital holographic microscopy has been widely used in vivo cellular observation, micro-optical components analysis, MEMS/MOEMS dynamic analysis, and many other fields. Otherwise, its application is limited by a certain field due to the low resolution of digital recording device, the recording system with low numberical aperture and speckle noise. This dissertation is concentrated on the research to enlarge the application and slove the problem that the interference fringes are formed in a limied region when using the low coherent light source in digital holographic micrscopy. The hardware control and data processing problems are also tackled with in the design and building the digital holographic microscopy system.Then main innovative works are included as follows:1. In order to measure the phase distribution of micro-optics element large that has large surface curvature in digital holographic microscopy, the method that uses the refractive index matching liquid to reduce the transmission frequency of object wave is proposed. It is very significant for measure the surface profile of micro-optics element that has the large curvature surface under the low numerical aperture of the system; then, this paper proposes a method that measures the average refractive index and surface profile of micro-optics element based on the dual wavelength digital holographic microscopy. The topography of micro-optics element can be measured when the refractive index distribution is unpredictable.2. The morphology of human red blood cells and mice fibroblast cells were observed in vivo by digital holographic microscopy. Experimental results have been proved that the digital holographic microscopy is a method that can observe the morphology of transparent or translucent biological cells. Experimens showed that the phase distribution of mice fibroblast at the early stage of the division have obvious change. When the division is completed, the phase distributions of the new cells are similar to the normal cells.3. A new recording method based on scanning the optical path difference is proposed in low coherent off-axis digital holographic micrscopy, due to the cohrenet length of the light source will limited the detected area of the object wave. The different areas of the detected plane are scanned by changing the optical path difference between the reference wave and object wave. Then, the phase distribution of each scanning area can be obtained by numerical reconstruction for each scanning area of digital hologram. At last, phase stitching technology is applied to stitch each scanning area to achieve the full field of the view of the object wave. Optical experiment is performed to demonstrate its validity.4. In the two step phase shiftting digital holographic microscopy, an iterative method to extract actual phase shift is proposed according to the resolution of reconstruction is determined wheather extraction actual phase shift. This method using an iterative algorithm to extract the actual phase shift in which the uniform of the reconstructed reference wave is taken as a judging condition.5. In order to achieve a long and real time observation for the biological cells, design and build a set of transmission type digital holographic microscopy system. The hardware control system and the data processing system are designed and completed, and then we the observate the mice fibroblasts by this system.The main content of thesis is included as follows:First of all, the paper discussed the basic principle of digital holographic microscopy, including recording and reconstruct method of digital hologram, phase extraction method. Secondly, this paper foucuses on the measurement method when the digital holographic microscopy is applicated in surface profile of micro-optical elements and cell observation in vivo.the theoretical and experimental research has been carried out. In order to measure the phase distribution of micro-optics element large that has large surface curvature in digital holographic microscopy, the method that uses the refractive index matching liquid to reduce the transmission frequency of object wave is proposed. It is very significant for measure the surface profile of micro-optics element that has the large curvature surface under the low numerical aperture of the system; then, this paper proposes a method that measures the average refractive index and surface profile of micro-optics element based on the dual wavelength digital holographic microscopy. The topography of micro-optics element can be measured when the refractive index distribution is unpredictable; finally, the morphology of human red blood cells and mice fibroblast cells were observed in vivo by digital holographic microscopy. The experimental results have been proved that the digital holographic microscopy is a method that can observe the morphology of transparent or translucent biological cells. Experimens showed that the phase distribution of mice fibroblast at the early stage of the division have obvious change. When the division is completed, the phase distributions of the new cells are similar to the normal cells.Due to the long coherent length of laser light, optical path length resolution in laser based digital holographic microscopy suffers from laser speckle noise and parasitic interferences caused by multiple reflections within the experiment setup. In order to solve these problems, low coherent digital holographic microscopy is carried out by the study of theory and experiment. In the low coherence off-axis digital holographic microscopy, the interference fringes are formed in a limited region due to the coherence length of light, resulting in a corresponding decrease of the detected area of object wavefront. A new recording method based on scanning optical path difference is proposed, the experimental results of the USAF1951demonstrate the validity of this method. However, the detected area of object wave is enlarged with the expense of measuring speed, and it is only applicable to static objects. In low coherence coaxial digital holographic microscopy, the detected area is not affected by the light source coherence length, but whether the actual phase shift can be exactly extraction will seriously affect the resolution. Therefore, an iterative method to extract actual phase shift in two-step phase-shifting digital holographic microscopy is proposed. Optical experiments are performed to demonstrate its validity by using a step type sample.Thirdly, a transmission type of digital holographic microscopy is builded and designed. The control software of the hardware system and data processing system is developmented. The experimental results of cell fusion are shown that the system can be applied to the field of observe the biological cells in quantitatively.Finally, summarized the existing research work, and puts forward the focus and problems to be solved in the future.