Studies On Diffraction Efficiency Of Harmonic Diffractive Optical Elements

Taking the traditional optical lenses and diffractive optical elements into comparasion,diffractive optical elements(DOEs)have been widely used in the optical system due to the special imaging characterizes in diffractive-refractive hybrid imaging optical systems.The traditional single-layer diffractive optical elements(SLDOEs)have the special characterists of absolute negative dispersion as well as small abbe number,but when the incident wavelength of hybrid optical systems is not equal to the designed wavelength of DOEs,the diffraction efficiency value will be deduced,which can not achieve 100% any more.However,the multi-layer diffractive optical elements(MLDOEs)can satisfy the high diffraction efficiency over the broad waveband.However,the SLDOEs and MLDOEs cannot be able to meet the design requirements of multi-wavebands imaging optical systems design at the same time.In view of the above analysis of the traditional single-layer diffractive optical elements theory and processing technology,harmonic diffravtive optics have been put forward for the improvements of the design principle and processing technology,which can solve the disadvantages of traditional single-layer diffractive optical elements that cannot satisfy the shortcomings of multi-wavebands of imaging optical system design.By calculating the microstructure height value of the harmonic diffractive optical elements(HDOEs),the harmonic diffractive optics can achieve 100% diffraction efficiency at the separtely harmonic wavelengths.The harmonic diffractive optics have been analyzedand the key factors that can affect the diffraction efficiency of harmonic diffractive optical elements in diffractive-refractive optical systems have been studied including the overall diffraction efficiency,environmental temperature change and the influence of manufacturing errors.In the first part,the development,processing,detection and research theory of diffraction optics have been studied.In the second part,the imaging theory of harmonic diffraction optical element has been discussed,and the design of harmonic diffractive optical element has been completed by scalar diffraction theory.In the third part,diffration efficiency characterists of harmonic diffractive optical elements have been studied and calculated.According to the sclare diffraction theory,diffraction efficiency of harmonic diffractive optics used in imaging hybrid optical systems has been studied.At first,the multi-level phase gtarings have been studied,design principle and diffraction efficiency characterists of SLDOEs have been studied;then,according to the amalysis measures for SLOEs,the basical imaging principle and diffraction efficiency characterists for harmonic diffractive optical elements have been derived;and finally,the diffraction efficiency of harmonic diffractive optical elements used in visible,middle and long infrared wavebands imaging optical systems.Thses made great foundations for the following contents.Environment temperature changing is very common for optical systems design and usage.In the fourth part,based on the basical imaging principle of harmonic diffractive optical element,the effects on diffraction efficiency characterists can be qualitatively analyzed.The model for effects of environment temperature on micro-structure height of harmonic diffractive optical elements,the mathical expressions of diffraction efficiency and polychromatic integral diffraction efficiency caused by environment temperature have been derived.Then,when using harmonic diffractive optical elements in visible,middle-infrared and long-infrared wavebands have been calculated.The research results show that the wavelengths that can meet 100% diffraction efficiency drift towards in the direction of long wavelength with the environment with the increase of environment temperature and the harmonic wavelengths drift towards in the direction of short wavelength.The research method and results have importanct meanings in hybrid optical system optimal design and image quality evaluating with environment temperature change.Manufacturing error is inevitable in the processing of harmonic diffractive optical elements manufacturing.In the fifth part,the effects on diffraction efficiency characterists caused by surface roughness and manufacturing errors of harmonic diffractive optical elements have been studied systematically in this part.Firstly,the mathematical models of harmonic diffractive optical elements and suface roughness have been set up,and the corrsponding mathmatical have been derived.The effects on diffraction efficiency caused by surface roughness resulting from the knife of single point diamond turning in the middle-infrared waveband and long-infrared waveband wavelengths as well as the dual-band infrared harmonic diffractive optical elements has been analyzed.The results show that effect on diffraction efficiency by surface roughness is small.Then,the types of manufacturing errors have been analyzed by single point diamond turing,the model of manufacturing errors and microstructure height for HDOEs and been set up and the mathmatical expressions have been derived.According to the harmonic diffraction theory,an example of effects on diffraction efficiency for harmonic diffractive optical elements used in dual-infrared waveband has been studied.Finally,based on effects on polychromatic integral diffraction efficiency(PIDE)caused by manufacturing errors,the manufacturing errors tolerance have been adopted and analyzed.The reaearch results show that micro-structure height errors have great influence on diffraction efficiency on HDOEs.So,it should be controlled preciously during manufacturing.Results can be implemented to dual-infrared waveband harmonic diffractive optical elements processing and errors control in diffractive-refractive hybrid imaging optical systems imaging quality evaluation.In the sixth part,based on the diffraction efficiency characteristics and its special imaging characteristics of HDOEs,a dual-band infrared optical system is optimized and designed,and its diffraction efficiency,machinability and farbricating errors are systematically analyzed.After optimal design,the optical system achieves high imaging quality in the dual bands,simplifies the optical structure,and achieves chromatic aberration correction,laying a certain foundation for the development of dual-band and even multi-band optical systems.