Design Of Microscope Objective With Deep Depth Of Field Based On The Wavefront Coding Theory

The microscope objective is one of the most important optical instrument, widelyused in every field to observe the micro-structure of the object’s inner. However, thereare two problems will greatly restricted to the microscope objective’s three-dimensionobservation ability. One is the contradiction between the high resolution and the deepdepth of field. The other is that the existences of the spherical aberration will seriouslydecreade the image quality. Wavefront coding as a new imaging technique can be usedto extend the depth of field of the incoherent imaging systems. With the characteristic ofmaking the system not sensitive to defocus, it can partly restrain the influence of theaberrations. Based on the feature of the wavefront coding system not sensitive todefocus, the analysis of the sensitivity to spherical aberration is deeply analysised.Therefore, the deep depth of field microscope objective is designed based on thewavefront coding theory. The main research contents are as follows:The theory of the microscope objectives and the characteristics of the wavefrontcoding system are analyzed, to be the foundation of the whole essay. According to themicroscope objective imaging theory, the imaging characteristics are analyzed. Pointedout that the depth of filed mainly affected the three-dimensional observation ability ofthe microscope objective, and the influence of the spherical aberration can not beignored. From the view of encoding and the decoding theory, the insensitive to defocusis analyzed, which laid the foundation of the deep depth of field microscope objectivedesign based on the wavefront coding.In the spatial domain, the sensitivities of wavefront coding to the sphericalaberrations are investigated. According to the relationship between wave aberration andray aberration, the ray aberrations of wavefront coding systems suffering from sphericalaberration and defocus are derived. Some analytical expressions for the upper and lowerboundary of ray aberrations are obtained by ray aberrations theory. With the propertiesof single-dimensional ray aberration and spot diagrams, the imaging characteristics ofwavefront coding systems suffering from primary spherical aberration and defocus areanalyzed.In the frequency domain, the sensitivities of wavefront coding to the sphericalaberrations are investigated. The expression of the OTF of the wavefront coding system suffering from spherical aberration is derived by the stationary phase method. The effectof the spherical aberration on the performance of the wavefront coding system isanylysed. The influence of variety parameters of phase mask on the the characteristicsof the wavefront coding system is anylysed. Compared with the insensitivity to defocus,the sensitivity of wavefront coding to the spherical aberration of the wavefront codingsystem is further analyzed. Besides, the characteristics of the wavefront codingsuffering from primary spherical aberration and defocus are analyzed in the spatialdomain, which verifies the validity of the conclusion obtained in the frequency domain.The deep depth of field microscope objective is designed based on the wavefrontcoding theory. The magnification and numerical aperture of microscope objective arerespectively100and1.1. The wavefront coding theory not only extends the depth offield, but also controls the influence of spherical aberration on the image characteristic.The design is an example to demonstrate that the wavefront coding adapts to improvethe microscope objective’s three-dimension observation ability.