Theoretical And Experimental Study Of Conical Diffraction In KTP

The conical diffraction of biaxial crystal is a kind of singular optical phenomenon which forms a hollow cone in space.In order to apply the properties of conical diffraction in the fiber optic rotary joint,to deepen the understanding of conical diffraction and to promote the development of conical diffraction applications,this paper studies the theory and experiment of conical diffraction.The conical diffraction formula of the biaxial crystal with curved rear surface is proposed,and the incident angle of the conical diffraction is calculated when the front surface of the crystal is not perpendicular to the optical axis.This study reduces the requirements for the crystal surface shape and processing deviation,which may be helpful for the integration of the devices in the optical path of conical diffraction.Based on angular spectrum diffraction theory,conical diffraction formula for ABCD optical system is given,thus the conical diffraction pattern behind the crystal can be calculated,which expands the application range of conical diffraction.In order to study conical diffraction of incident beam with no analytical expression,and to improve the simulation efficiency,we proposes a new method for calculating the conical diffraction intensity based on the fast Fourier transform?FFT?,and derives the condition of width for the diffraction field in order to meet the sampling theorem,which promotes the development of the study of conical diffraction with complex incident beam and rapid calculation of the conical diffraction.The major achievements in this dissertation are as follows:1.The angle of intersection between the incident beam to the optical axis of the crystal versus the conical diffraction pattern is studied,and a scheme of the angle measurement based on the conical diffraction is presented.The conical diffraction formula of a crystal with curved surface is given.A conical diffraction experiment is carried out on crystal with a spherical surface.The incident angle of conical diffraction is calculated,when crystal is not cut perpendicular to an optical axis.2.We propose a conical diffraction formula contains an image lens,and the conical diffraction pattern behind the image lens is experimentally studied.The dirived the conical diffraction formula is extended to the optical system described by ABCD matrix.And to verify the accuracy of the formula the experiment of conical diffraction across a couple of lenses is carried out.3.A calculation method of conical diffraction based on fast Fourier transform is put forward,and the sampling conditions of transfer function of conical diffraction is deduced.The effects of sampling in spatial domain and truncation in frequency domain are also discussed.Moreover,we simulated the conical diffraction of incident beam passing through different sizes of square aperture,and found different phenomenon from that of Gauss beam under?₀<1.The experiment of conical diffraction with a beam though a square aperture has been carried out,which shows agreement with calculation and verifies the reliability of our method.