Research On Focal Length Measurement Technology Of Large Aperture Telephoto Spherical Lens Based On Reflective Fresnel Band Hologram

Large aperture long-focal slow lenses are key components of high-power laser facility,which are used to collimate and filter laser beam,transmit energy.Focal length testing is the hot spot of optical measurement.A theoretical approach for focal length measurement has been established with the characteristics of convex reflecting mirrors of binary diffractive optical elements.Moreover,based on the wavefront measurement,it’s also determined to construct a design policy for the focal length measurement and a design thought of low cost and high precision in association with the actual needs of high-power laser facility.Besides,the theoretical calculation method of the equivalent curvature radius and the zone radius of the FZP has presented by means of studying the basic theory of Fresnel diffraction with a focus on the theoretic model of the compensated null interferometry long-focus measurement method centering on FZP.On this basis,the impact of key parameters of grating design,such as duty ratio,and etch depth on fringes interpretation has been analyzed to present related recommended values for related parameters with Cat’s eye fringes as the criterion of null interferometry.Meanwhile,the null method of focal length measurement has been implemented by achieving the design of anaberration of the measuring optical path via the ray tracing approach and the simulation with the Zemax software.With the above theoretical work,the overall structure of the focal length measurement system for the FZP method can be constructed with the presentation of design schemes,commissioning and measuring methods as well as equipment selection of sub-modules of the system in accordance with the system design policy and thought.At last,sources of measurement errors and the effect of focal length measurement have been analyzed in terms of the mathematical model of the focal length measurement and structural characteristics of the system.In this dissertation,the whole measure system is constructed.Three large aperture slow lenses whose focal length are 12000 mm,13500mm and 312500 mm are tested in compared testing.The result shows that the reproducibility of this measure system is better than 0.03%,as well as other advanced long focal length measurements.