Experimental Study On Digital Holography Of Rough Surface Micro - Morphology

The surface of photoelectric device and precision machinery parts are rough surface with certain shape and morphology. Surface topography is one of important factors determining the mechanical, thermal and electrical properties of combination surface, and the testing and measuring problems of rough surface micro morphology, is the basic problem of researching contact mechanics, thermal and electrical properties. Digital holography can quantitatively obtain the measured surface micro topography information, has the advantages of non-contact, high precision, high efficiency, which provides a new approach for precision metering detection of structure and the device surface, the main work is as follows:(1) Based on fresnel diffraction integral, the principle of the record and reconstruction process of digital holography is analyzed, and three kinds of standard reconstruction algorithm are discussed. To establishing the mathematical model for recording and reconstructing hologram, used S-FFT and convolution algorithm to simulate the generation and reconstruction process for off-axis digital hologram.(2) In order to obtain high quality digital hologram, the influence of structural parameters of CCD, such as the size of the pixel, sensitive area and sampling interval is analyzed. According to sampling theorem and spectrum separation requirements, the set conditions of the optical path parameters in off-axis digital holography for rough surface are given. The phase unwrap algorithm is researched, and the good reconstructed distance in digital holography is determined.(3) The facts that influence the quality of reconstructed image are discussed. The methods include average eliminate, spectrum filtering, image plane filtering are researched. For speckle noise, the median filtering algorithm, Lee filtering algorithm, Kuan filtering algorithm are introduced to filter this noise. The results show that Kuan filtering algorithm was better in rough surface digital hologram.(4) Using reflective off-axis digital holography to measure the roughness of metal surface. The relationship between reflective micro surface morphology and reconstruction phase is derived, and surface topography was obtained quantitatively, receiving the roughness value after data processing. Applying this system to measure roughness of 1.60 and 0.8 standard planning sample block, it’s rough value is 1.62μm,0.79μm respectively, the roughness of 1.6 standard shaping sample block, it’s rough value is 1.66μm. Relative error are 1.25%,-1.25%,1.66%. The experimental results show that, the advantage of digital holographic technology in metal surface is high precision, and the measurement device is simple, the measured object is not affected by the way of processing etc.(5) The off-axis digital holographic transmission system is designed and built. The measurement principle for transmission object using digital holography is reduced. Applying this system to measure the three-dimensional morphology of the Len and then its profile 3D is obtained.