Study Of The Three-dimensional Surface Topography Measurement Based On Dual-wavelength Digital Holography

The surface topography measurement is more necessary with the fast development of ultra-precise and micro-fabrication technology recently.Vast of methods of surface topography measurement have been emerged.Digital holographic technology which is one of those methods has been widely used with advantage of high-precision,non-contact,and real-time measurement.Based on traditional digital holography,dual-wavelength digital which combines traditional digital holography with dual-wavelength technology has been proposed.And then,it is used to measure the surface topography.In the numerical reconstruction of traditional digital holography,the phase distribution is always wrapped due to the optical path difference(OPD)are longer than the wavelength.This phenomenon is called phase imaging ambiguity.In order to get the real phase,we need to eliminate the phase imaging ambiguity.Usually,the process is very complex,and it also brings in some errors.Thus,the measurement accuracy will be reduced,especially for objects with complex structures or large surface gradient.The dual-wavelength digital holography can directly obtain the real phase information without a complex unwrapping process by using the longer equivalent wavelength.The paper mainly focuses on the study of surface topography measurement using dual-wavelength digital holographic technique.The following work has been done.1.Based on the theory of digital holography,dual-wavelength digital holographic technique which is used to measure the surface topography is proposed and the advantages of the method also have been introduced.2.The process of surface reconstruction is simulated by building a mathematic model.The feasibility and effectiveness of dual-wavelength digital holography has been verified through the result of simulating.3.Then experimental system has been carried to harvest some holograms of transmission-type objects and reflective-type objects respectively.The result shows that dual-wavelength digital holography is reliable because the measurement data and standard values are consistent well.4.Finally,the wavelength drifts error has been analyzed in detail.