Research On The Digital Holography 3D Surface Profiling Measurement

Digital holography detection is an important method for laser nondestructive testing technology, which uses digital way to realize its record, storage and reconstruction process. In the domain of nondestructive testing such as contour measurement, micro-circuit detection, stress testing, observation of biological cells, deformation and vibration measurement, the features and advantages of digital holography detection can be fully displayed, therefore, it has a broad prospect.With the development of mechanical micro-processing skill, microelectronics technique, biotechnology, information technology and material science, nondestructive and whole-field measurement for micro object surface is needed in many fields of science and technology. Optics measuring technique is a widely applied method for 3D surface profiling, and there are some common methods:computer vision, phase measurement profilometry (PMP), triangulation and Fourier transform profilometry (FTP) and so on. But optics surface profilometry only can be suitable for object with continual surface. Moreover, low-correlation interferometry and wavelength scanning interferometry only also can be applied to stepped surface and diffuse reflected surface. Thus these methods don't suit for small and complex 3D surface profiling (like MEMS devices).3D surface measurement with real-time non-contact, large depth, high resolution and long work distance can be realized using digital holography detection, combination of interferometry and computer 3D imaging, in which micro feature can be easily embedded, so it is suitable for 3D surface profiling of small object. Therefore, digital holography 3D surface profiling is adopted to realize 3D contour measurement for small object in the paper. Moreover, detection formulae for optical rough objects are derived based on statistic optics and scalar diffraction theory and the detection principle of the tilt of object illumination is briefly discussed.To improve the quality of reconstructed image, it is important to eliminate zero-order and conjugate image, thus the elimination methods are also discussed. Additionally, to be convenient to detect objects with different sizes using digital holography, in general, the object wave is transformed by optical systems with different magnifications and then reached CCD. So the problem of diffraction calculation in which the optic wave passing through an optical system is involved in the reconstruction. Based on the coherent imaging theory, two methods using classical difffraction integral to reconstruct object plane optic wave field are also discussed for realizing wavefront reconstruction after the object light passed through an optical system and then reached CCD.