Research On Key Technologies Of Mid-infrared Immersed Echelle Grating Spectrometer

The spectrometer is an essential optical instrument that combines optical technology,computer science and technology,and electronics and is an essential medium for spectral analysis.With the help of spectrometers,we can measure and analyze the composition,internal structure,and other characteristics of certain substances.With the requirements and applications of grating spectrometers in various fields,grating spectrometers are developing rapidly.They are widely used in astronomy,defense,agriculture,biology,and other fields and are gradually developing toward high accuracy,portability,and lightweight and compact.Wide-band infrared high-resolution spectrometer has been a major challenging topic for space and airborne missions and ground-based telescopes.However,due to the limited capabilities of conventional spectrometer technology,traditional Fourier transform spectrometers have extremely high background noise,which limits their sensitivity to observing faint objects.They are too bulky to accommodate long scans of the interferometer arm to achieve high resolution.To realize the scientific need for detection studies in the mid-infrared band of remote sensing,this thesis carries out research work based on the technology of an immersion echelle grating infrared spectrometer,where a high dispersion diffraction grating is combined with a low-resolution cross-dispersion grating to address the technical difficulties faced by infrared spectroscopy observation equipment.This thesis focuses on immersion grating spectrometer,spectrometer optical system design,immersion grating process and test,and stray light analysis and the main research work as follows:1.Introduces the background and development process of echelle gratings,reviews the advantages of planar reflection echelle gratings,immersion gratings in highresolution spectrometers,and the current status of domestic and international research on related applications,and analyses the limitations of reflection echelle gratings in the infrared band.2.According to the design parameters and related theories,Designed the optical system of the spectrometer.A scheme for a mid-infrared high-resolution cross-dispersion spectrometer based on Three-Mirror Anastigmat system(TMA)combined with an echelle grating theory was proposed.The chromatic aberration-free,large field-of-view,and compactness of the TMA optical system are exploited to achieve a high-resolution,lightweight spectrometer design.3.A double grating immersion spectrometer is proposed.The double roles of collecting and dispersion of the concave grating is utilized to simplify the system structure.The system optical throughput is increased under the concave grating Wadsworth configuration.The Czerny-Turner spectrometer is combined with an immersion grating using the optical design software Ansys Zemax.The relationship between imaging performance and optical parameters is analyzed,and on this basis,a detailed design method for this type of spectrometer is proposed.The passive athermalization design of the convergent system is also presented;the system optics are evaluated utilizing Spot Diagram,Enclosed Energy,and other indicators.4.The spectral dispersion technology of the immersion grating is studied,starting from the optical properties of infrared materials and analyzing the key factors affecting the material of the immersion grating.In addition,the parameters of the grating,including the blazed angle,the grating constant and the diffraction area,are calculated.The internal absorption loss of the material and the Fresnel loss of the dielectric surface are analyzed and discussed.Based on the rigorous coupled wave method(RCWA),the TE/TM reflection characteristics and field distribution of the immersed grating in the mid-infrared band were analyzed by Rsoft Diffract MOD module and Gsolver grating design software.5.The stray light of the optical system is analyzed,and the source of stray light of the immersion grating spectrometer is analyzed.Combined with the stray light analysis software Tracepro,the stray light suppression point source transmittance(PST)and effective emissivity are calculated.The results show that the stray light suppression ability meets the requirements.