Studies On Diffraction Effciency Of Diffractive Optical Elements In Infrared Wavelengths And Machining Error

Diffraction efficiency is an important characteristic of the diffractive optical elements.The diffraction efficiency effects directly on optical properties and application of DOEs in refractive/diffractive hybrid optical system. This paper studies mainly the effect of air gap size on diffraction efficiency for double-layer diffractive optical element(MLDOEs), and gives an example that analyzes the applications of MLDOEs in infrared optical system.First of all,in this paper,based on the scalar diffraction theory and the phase grating grating equation,as the basis theory of diffraction efficiency of diffractive optical.The relationship between the wavelength and diffraction efficiency about the single-layer diffractive optical element,harmonic diffractive optical element,multi-layer diffraction optical element in the infrared wave band is analyzed. Through the analysis of diffraction efficiency with oblique incidence of single-layer diffractive optical elements and double-layer diffractive optical elements,the influence of diffraction efficiency with different incident angle in the infaraed wavelengths is discussed. At the same time,through analysis of Debye-Waller formula, the influence of surface roughness of difffraction optical element and diffraction effciency is discussed.The second, based on the rmodel of relationship between diffraction efficiency and tilt error errors for MLDOEs, the relationship between diffraction efficiency and assembly errors is disscussed. Besides,through the analysis of periodic width error about double-layer diffractive optical element,the mathematica model of the relationship between air gap and diffraction efficiency is established, the influence of diffraction efficiency of double-layer diffractive optical elements and air gap in different period and different incidence angle is discussed.At last,infrared imaging system including MLDOEs is designed by selecting ZnS and ZnSe as the base material. Based on the bandwidth integral average diffraction efficiency theory, the impact of air gap size of double-layer diffractive optical elements on the performance of MLDOEs is validated further.