Study On Diffraction Characteristics And Absolute Compensation Mosaic Technique Of Echelle Grating

Echelle grating is the core dispersive optical element in the fields of astronomy,spectral analysis,lithography and optical communication because it works at large diffraction angle and high diffraction order and has the characteristics of high dispersion,high resolution and wide band blaze.According to the current grating engraving level,the echelle grating with the engraving width less than 500 mm is mainly made by mechanical engraving method with simple production process.The echelle grating with the engraving width greater than 500 mm is mainly made by mechanical mosaic method with low cost and low difficulty coefficient.The mechanical mosaic method is to adjust the position and attitude between the tiled gratings and adjust the phase of each grating to the incident light,so that the tiled grating can be used as a perfect grating under certain wavefront requirements.In recent years,with the development of astronomy,the aperture of telescope is becoming larger and larger,and the aperture of echelle grating required by astronomical high-resolution spectrometer is becoming larger and larger,and the mosaic of echelle grating is more and more concerned by scholars at home and abroad.At present,although foreign countries have the ability to tiling and copying the echelle gratings,the tiled echelle gratings can only be used in specific conditions,and can not be used as a perfect echelle grating.In China,it is still in the research and experimental stage,and it does not have the ability to mosaic large aperture echelle gratings.In view of this,this paper has carried out the research on the diffraction characteristics and absolute compensation mosaic technology of echelle grating,aiming at solving the problems of the design of the echelle grating with high diffraction efficiency,the separation and detection of the mosaic error of the echelle grating,the calculation of the mosaic error of the echelle grating,the calculation of the mosaic error tolerance of the echelle grating,and the design of the mosaic error correction device of the echelle grating.The specific research contents of this paper are as follows:First,the analysis of diffraction characteristics of echelle grating.The influence of incident light information,such as incident light wavelength,incident angle,azimuth angle,polarization state and grating information,such as blaze angle,line density,groove depth and surface metal material,on the diffraction efficiency and polarization characteristics of echelle grating is simulated and analyzed based on PCGrate software.The diffraction characteristics of echelle grating are summarized,and a method to improve the diffraction efficiency of grating by changing the groove depth of grating is proposed.The effectiveness of the method is verified by the experiments,which provides sufficient guidance for the design and application of echelle grating with high diffraction efficiency;Second,the establishment of the mosaic error calculation model of the echelle grating.Based on the three-dimensional spatial relationship matrix between the tiled gratings,the relationship equation between the tiled gratings can be established,and then the plane equation of the grating surface can be established according to the plane fitting of the least square method and the spatial three-dimensional transposition matrix between the grating and the detector.Finally,according to the plane equation of the grating surface and the relationship equation between the gratings,the calculation equation of the mosaic error between the gratings can be established and the error between the tiled gratings can be calculated by the diffraction wavefront obtained by the interferometer.This model provides a method to evaluate the mosaic quality from the perspective of error and provides theoretical guidance for the numerical mosaic of gratings;Third,the establishment of the mosaic error tolerance calculation model of echelle grating.According to the analytic hierarchy process(AHP),the comparison matrix of mosaic errors can be established,and then the calculation matrix of mosaic error weight can be derived.Then,according to the relationship between the mosaic error and the diffraction wavefront of the tiled grating,the calculation matrix of the maximum mosaic error can be derived.Finally,according to the calculation matrix of the error weight and the calculation matrix of the maximum error,the calculation matrix of the mosaic error tolerance can be derived.Through simulation and experiment,the results show that the theoretical model is correct,which provides the mosaic index for the mosaic of echelle gratings and provides guidance for the design of mosaic error correction device;Fourth,the research of the separation detection method of the mosaic error of the echelle grating.The zero-order diffraction light of the echelle grating is weak,so the separation detection and correction of the mosaic error cannot be realized by using the zero-order and non-zero-order diffraction light of the grating.Therefore,based on the relationship between the mosaic error of the echelle grating and the diffraction wavefront,a four-interference field error separation detection method is proposed,that is,the error separation detection method is based on the difference between the interference field formed by the diffraction light of the same diffraction order at different incident angles of the echelle grating and the reference light.Based on this method,the high-precision mosaic of the echelle grating is completed experimentally,which provides basic conditions for the mosaic of the echelle grating.Fifth,the design of the device for correcting the mosaic error of the echelle grating.According to the structural characteristics of flexure hinge and the principle of four point control plane rotation displacement,the in-plane error correction device and non coplanar error correction device are designed respectively.The adjustment accuracy of in-plane rotation error can reach 0.129 ?rad,the adjustment accuracy of non coplanar rotation error can reach 0.167 ?rad,and the adjustment accuracy of translation error can reach 10 nm,which can meet the accuracy requirements of mosaic gratings.Through the stress mode analysis and experiment,the results show that the device has certain stiffness and stability,and has the ability of tiling the echelle grating,which provides the basic conditions for subsequent grating tiling.