Research On Imaging Technology Of Large Depth Of Field Baised On Nondiffracting Beams

An optical imaging system with large depth of field has features of greater imaging space, without requiring mechanical focusing and displaying 3-D objects. Therefore, it has been an active research topic to extend the depth-of-field of optical imaging systems. The non-diffracting beam has the characteristics of focal segment, so it can be used to extend the depth-of-field of an imaging system.The main research and innovations are as follows:The diffracting patterns produced by the axicon in different light illuminating are analyzed, and the mathematical models of these patterns are theoretically established. Based on the diffraction pattern of the axicon in monochromatic parallel light illumination, the diffraction patterns of the axicon illuminated by converging and diverging waves produced by an axis point are derived. Moreover, the diffraction patterns of the aixcon illuminated by quasi-monochromatic light and polychromatic light are presented based on their spectrum characteristics.The interference pattern of two non-diffracting beams is analyzed. Two non-diffracting beams are gene rated when an axicon is illuminated by two coherent beams, which are produced by two pinholes illuminated by a monochromatic wave. Based on the non-diffracting property of an axicon in oblique illumination, the interference field is the linear superposition of each non-diffracting field of non-diffracting beam, namely the interference intensity is the sum of the two zero-order Bessel functions. The locus of inte rfe rence f ringes is analyzed to be hyperbola according to the formula of dark fringe.Three common large depth of field imaging systems are designed and produced. The axcion can produce a non-diffracting beam, and it is used to extend depth of field of optical imaging system, and the theorem of this method is analyzed in this paper. According to the different applications, three optical systems with large depth of field 1:1 imaging system, microscopic imaging system and telescopic imaging system are designed.The form and characteristics of the point spread function (PSF) of the designed imaging systems are derived based on the 1:1 imaging system. The changing rule of the point spread function centre spot is analyzed, and the rule gives the reason of the changing of the images quality, and provides a theoretical basis for image restoration. The imaging system is analyzed theoretically from OTF (optical transfer function), resolution, contrast and depth of field.Four tranditional image restoration methods: wiener filtering, constrained least squares filtering, Lucy-Richardson algorithm and blind deconvolution are introduced, and the experimental results used these four methods are compared. A multiple images superposition algorism is introduced based on the properties of the pictures imaged by the designed optical system. Since the PSF except the center spot spreads out on the full image, which makes the contrast be lower, and makes the details of image immerse in large noise. In order to improve the contrast and definition of the image, this effective algorism is presented.Imaging experiments were steped to use the designed three imaging systems to image with the objects of letter, pattern and space continuous object. Experimental results show that these three imaging systems, designed based on the non-diffracting beam, have larger depth of field than ordinary optical systems. Therefore, the performed experiments validate the effect and feasibility of non-diffracting beam for imaging with extending depth of field.