Research On Phase Shift Digital Holographic Microscopy

Digital holographic microscope is the application of digital holography technology in the field of microscopy.Hologram formed by interference of CCD recorded with object beam with the height information of the measured object and reference beam.The three-dimensional shape reproduction of the object is realized by reconstructing the light intensity and phase information of the object by using an algorithm in the computer.Digital holographic microscopes have their own advantages over other microscopes.Traditional optical microscopes can only record the light intensity information of an object.Therefore,only two-dimensional information of the object can be obtained.Although electron microscopes have high resolution and high magnification,but the cost is very expensive,and the volume is very large and heavy.Polarizing microscopes are only suitable for birefringent samples.Atomic force microscopy is very easy to damage the surface of the sample because it is a contact measurement,and the AFM probe is also easily broken.Therefore,digital holographic microscopy can be applied to biological cell detection,MEMS device surface measurement,gas density and so on.Digital holography can be divided into off-axis holography and coaxial(Phase-shift)holography from the angle of two beams.We use coaxial phase-shift holography to achieve three-dimensional reconstruction of digital holographic microscopy.Compared with off-axis digital holography,the phase-shifted digital holography eliminates the limitation of the angle between the object beam and the reference beam,reduces the adjustment difficulty and accuracy requirements of the experimental device,and increases the efficiency of the CCD.In addition.synchronous phase shift digital holography enables real-time measurement.In the experimental recording method.this paper discusses the piezoelectric ceramic driving method and the polarization phase shift method.After obtaining the digital hologram,the hologram is preprocessed to reduce noise interference.The hologram is digitally reconstructed by a reconstruction algorithm.After the reconstructed phase map is obtained,it is filtered to further improve the image quality.Then.unwrapping the phase and the phase distortion is compensated to obtain the true phase.The true shape information of the sample is restored by calculating the height.The traditional optical path was improved on the experimental device.and a set of holographic recording devices was designed and manufactured.The system was calibrated using the USAF1951 standard resolution board.The experiment proves that the system can realize the three-dimensional reconstruction of the surface of the micro-nano sample with good precision.