Study On 3D Height Of Objects Based On Dual Wavelength Digital Holography

Digital holographic is a novel three-dimensional imaging technique that combine the traditional optical holography and computer technology. With the fast development of the computer science and high resolution image sensor, digital holography has been gaining wider and wider attention. It has the properties of non-contact, non-destructive, high resolution and fast processing, and can been widely used in contour measurement, stress testing, observation of biological-cell imaging, micro-circuit detection and other fields.The paper elaborates the basic principles of digital holography, including the recording and reconstruction. We discuss three algorithms for diffraction propagation, namely, the Fresnel transform method, the Huygens convolution method, and the angular spectrum method (ASM). Comparing to the other two algorithms, ASM does not have any distance limitations and is easy for filtering noise, so it is best suited for the topography measurement of microstructure objects. Besides, we also present the theory of the three-dimensional topography measurement for microstructure objects.We systematically analyze the theory of dual-wavelength optical phase unwrapping and simulate the slope structure to show the feasibility of the technology. Besides, we study the principle of self-referencing Lloyd’s mirror interferometer and propose a digital holographic microscope optical system employing dual-Lloyd’s mirrors. With this system, the traditional dual-wavelength digital holographic microscope optical system has been simplified and the stability of the system has been enhanced, which makes it easier for measurement. Through three-dimensional shape detection of silicon oxide spheres, we demonstrate the accuracy and feasibility of the system.Further, we study the principle of lateral shearing interferometer and propose a dual-wavelength digital holographic microscope optical system based upon. Using the feature of lateral shearing interferometer, the system was simplified and applied to the three-dimensional height detection of the silicon oxide spheres. Experimentally, we demonstrate the accuracy and feasibility of the system.