Research On The Key Technologies Of Digital Holographic Microscopic Measuring

The digital micro-holography is an important means to measure microstructure of samples, and it is a technology with characteristics of simpleness, non-contact, dynamic and so on. The development of the digital micro-holography is summarized. It is a novel holographic imaging technique, which integrates optical holography principle, computer technology and photoelectric technology. In digital holography, the hologram is directly recorded on a charge-coupled devices(CCD) camera rather than a traditional holographic plate and the optical reconstruction is replaced by computer numerical reconstruction. So the full process including recording, storage and reconstruction is entirely digital.In this paper, digital holography technology and its application for microscopy are discussed. Especially three dimensional profile measurement of tiny objects is well studied by theoretical analysis, experimental and simulation. The main contents are as follows:Basic theories of digital micro-holography are first described, then the process of recording and reconstruction of the digital holographic were introduced starting from scalar diffraction theory. After that, two most common methods:Fresnel approximation and angular spectrum algorithm of numerical reconstruction are discussed and compared, angular spectrum is more suitable for our task. In the process of experiment, the recording distance and the angle between object light and reference light which would affect the quality of hologram are considered and obtain their range. On the basic of theoretical studies, a digital micro-holography measurement system without pre-amplification was established, then tiny object such as MEMS micro devices was measured and its reproduction three-dimensional contour was obtained. Based on angular spectrum algorithm, the program of digital holography reconstruction was compiled with the help of MATLAB software in the part of simulation. Combined with spectral filtering method, the zero order term and twin image which seriously affect the quality of hologram were eliminated, then a desired reconstruction image was made, so as to achieve the purpose of measure. At last, the depth of focus of the digital holographic imaging system was discussed, and the depth of focus is deduced and analyzed from reconstructed image quality.