Research On Surface Detection Technology Based On Incoherent Digital Holography

Ordinary photography records the amplitude(intensity)information of the light field and can only obtain a two-dimensional image of the object.The holography uses the principle of interference to record the amplitude and phase information of the light field to obtain the three-dimensional image of the object.Another advantage of holography is the ability to image phase objects,especially weakly absorbing or transparent biological samples.As a common light source that is ubiquitous and easy to obtain in life,incoherent light can effectively avoid problems such as parasitic interference and speckle noise in coherent light imaging.Incoherent digital holography is a promising three-dimensional optical imaging technology and is expected to be promoted to wider application fields.It uses a broadband light source as the illumination light source,photoelectric sensing elements(CCD or CMOS)replace the dry plate to record the hologram,and simulates the optical diffraction process on the computer.Among them,Fresnel incoherent correlation holography(FINCH)divides the light wave from the same point on the surface of the object into two beams by loading a phase mask on the spatial light modulator(SLM)and uses the self-coherence of the two beams to realize the recording of point source holograms.The linear superposition of all point source holograms constitutes the incoherent hologram of the object,which is recorded by CCD.FINCH technology has significant advantages in imaging resolution.Some studies have shown that FINCH-based fluorescence microscopy imaging technology can achieve resolution imaging beyond the Rayleigh diffraction limit from both theoretical and experimental aspects.In addition,the combination of helical phase modulation technology and FINCH technology can realize edge-enhanced imaging under incoherent illumination,obtain edge information of objects,and effectively describe the shape and detailed features of objects.Therefore,as an optical measurement method,FINCH technology has the advantages of noncontact,non-destructive,independent of the coherent light source,high lateral resolution,no scanning,easy to match with existing mature optical systems,etc.It has a very broad application prospect in the surface detection of tiny scratches.This paper mainly studies the imaging characteristics of FINCH system and its application in the field of surface detection.The specific content includes the following three parts:1.Theoretical analysis of the basic imaging principle of FINCH technology.By starting from an ideal point light source to analyze,the point spread function of the FINCH recording system is derived based on wave optics theory,and the imaging analysis of the USAF1951 resolution plate is carried out.The interferences of coaxial zero-order image and conjugate image are removed by using the averaging method and phase-shifting method,and the optimal reproduction distance is determined by combining with the angular spectral diffraction reconstruction.In addition,two denoising methods are introduced to improve the imaging quality.2.The factors affecting the spatial resolution of the lenticular FINCH system are systematically studied.It is found that the effective aperture of the FINCH imaging system is affected by the parameters of the image detector and the actual aperture of the point spread function.Simultaneously,unstained living biological cells and tiny scratches are imaged by combining FINCH with a microscope system.3.Research the basic principle of object edge-enhanced imaging realized by combining helical phase modulation technology and FINCH technology.For the FINCH system based on the phase modulation of the multi-mode Laguerre-Gaussian beam,the effect of radial quantum number and angular quantum number on edge extraction and detection is studied.The helical phase modulation of integer-order and fractional-order angular quantum numbers are introduced into the angular spectrum diffraction reconstruction process to achieve the effect of object edge extraction and enhancement.