Study On The Key Techniques Of Digital Micro-Holography

In this dissertation, digital micro-holography for the reconstruction of three dimensional profiles of the small or micro phase objects and its key techniques are studied.Based on digital micro-holography, several kinds of digital off-line micro-holographic systems are built and one kind of grating phase-shifting digital in-line micro-holographic system is presented to realize the reconstruction of three dimensional phase information of the tested phase objects including phase grating and living cell. In order to get the right reconstruction information of the original micro-structure or the profile, we have paid attention to the research of digital micro-holography, and propose four novel techniques as follows:1.Estimation technique of optimal reconstruction distance d and titling factors k_x, k_y of the numerical reconstruction waveThe reconstruction distanced and the titling factors k_x, k_y of the numerical reconstruction wave are three important parameters to realize the right numerical reconstruction of digital hologram. Their aberrations will effect the right information reconstruction, specially the phase information reconstruction. The presented new estimation method of the optimal reconstruction distance based on the revised average grad method suppresses the effect of the lateral resolution changing with the reconstruction distance on the estimation of reconstruction distance to get the exact reconstruction distance. While we carry out the titling factor k_x, k_y computed automatically according to the frequency-shifting characteristic of Fourier transform.2.Aberration correction technique based on phase subtraction method at the reconstruction planeAll kinds of the existing methods for the aberration correction of the reconstructed numerically phase of digital hologram have the different merits and disadvantages. We put forward a new phase subtraction method at the reconstruction plane, in which two holograms are digitally recorded and numerically reconstructed, respectively, and their reconstruction phase distributions are subtracted to reduce the phase aberration unwanted to get the exact original phase information. It can reduces the phase aberration from the light source, optical components and background, and while ensure that the phase of the recorded objects won't be subtracted mistakenly if some of the distributions of its sub-terms are similar with the phase aberration. The proposed method shows especially its advantages in the profile reconstruction of living cells.3.Aberration correction technique for the quadratic phase of pre-magnified digital off-line micro-hologramFor pre-magnified digital micro-holography, the compensation of the quadratic phase produced by micro-objective is vital. Aiming to the disadvantages of the existing compensating methods we propose a new reconstruction method, in which firstly the quadratic phase is compensated at the back focal plane of micro-objective, and then get the original object wave-field by diffraction calculation. The proposed new method reveals some advantages, such as the additional optical parts does not be added, the parameter in numerical compensation process shows unique, and only single hologram is needed.4.Processing technique of grating phase-shifting digital in-line hologramIn traditional phase-shifting in-line holography, the recording of hologram needs two beams because the reference light source must be added. The reconstruction of digital in-line hologram by single beam based on point diffraction theory has the limitations that the tested objects must be high transparent and their sizes need be less than one of the recording medium. We provide the grating phase-shifting digital in-line holography with Digital Micro-mirror Device(DMD). By taking advantage of the reflection and diffraction characteristics of DMD, it integrates the sine amplitude grating phase-shifting technique and diffraction processing technique into digital holography to realize the numerical reconstruction of in-line hologram, and then to get the original wave-field. Further, combining with the beam splitting characteristic of DMD, the grating phase-shifting digital in-line holographic orthogonal reconstruction system can be built, which provide the better way and feasibility for the high precision profile or structure reconstruction.