校谱线弯曲的共轴PGP成像光谱仪光学系统设计

Design of the Optical System of Coaxial PGP Imaging Spectrometer with Eliminating Spectral Smile

针对共轴棱镜-光栅-棱镜成像光谱仪的谱线弯曲难以校正的问题,提出了使用弯曲狭缝配合准直镜、聚焦镜畸变校正谱线弯曲的方法。该方法在保留棱镜-光栅-棱镜高衍射效率和光路共轴等优点的基础上,能够校正仪器的谱线弯曲和光谱弯曲。为了提高该方法的通用性,考虑狭缝、镜头畸变、光栅、棱镜等参数,建立棱镜-光栅-棱镜矢量色散模型,给出校正光谱弯曲和谱线弯曲的目标函数,并利用遗传算法对目标函数进行优化,快速计算不同狭缝长度时狭缝形状和镜头参数的最佳组合。用该方法的计算结果设计了一个狭缝长度为22 mm,工作波段为400~800 nm,光谱分辨率为2 nm,F数为3.5的弯曲狭缝PGP成像光谱仪光学系统,该系统谱线弯曲小于1μm,光谱弯曲小于0.7μm,且满足成像质量要求。设计结果表明,用弯曲狭缝配合准直镜、聚焦镜畸变的方法能够有效校正谱线弯曲。

Hyperspectral remote sensing technology is an optical remote sensing technology developed on the basis of imaging spectroscopy,which can realize comprehensive observation of spatial information,spectral information and radiation information.The imaging spectrometer adopting the Prism-Grating-Prism(PGP)spectroscopic element avoids the off-axis problem of traditional prism-type and grating-type imaging spectrometers,and is conducive to the miniaturization and compactness of imaging spectrometers.Aiming at the problem that the spectral smile of coaxial PGP imaging spectrometer is difficult to correct,this paper proposes a method to rectify the curvature of spectral line by using curved slit and distortion of the collimator lens and focusing lens.On the basis of retaining the advantages of PGP such as high diffraction efficiency and coaxial optical path,this method can correct spectral smile and keystone of the instrument.In this paper,the prism-grating-prism vector dispersion model is established by focusing on the influence of lens distortion,the number of grating lines and prism angle on spectral smile and keystone.By tracing the light vector and analyzing the intersection between the light vector and the image plane after the light vector passes through the PGP element with different parameters,the influence of different parameters on the smile was analyzed.It is worth noting that when the shape of the slit changes,the direction of the initial light vector also changes.Therefore,this model can also analyze the effect of the slit shape on the spectral smile and keystone.Further,the prism-grating-prism vector dispersion model is used to analyze the spectral line bending characteristics of coaxial PGP spectroscopic elements:when the coaxial condition is met,the PGP imaging spectrometer will inevitably have a large smile,and the spectrum is bent in the short-wave direction.After adjusting the prism Angle,the number of grating lines and the lens distortion,we analyzed the smile size of the combination of the above parameters,and came to an optimistic conclusion:the smile problem of the imaging spectrometer could not be eliminated only by changing the prism,grating and lens.However,the smile can be corrected well by the method of bending the slit and matching the appropriate lens distortion.In order to improve the versatility of this method,this paper gives an objective function for correcting spectral curvature and spectral line curvature by using the PGP vector dispersion model,and uses genetic algorithm to optimize the objective function and calculate the best combination of slit shape and lens parameters quickly.In order to verify the feasibility of this method,this paper uses the calculation results of this method to design a curved slit PGP imaging spectrometer with a slit length of 22 mm,an operating wavelength of 400~800 nm,a spectral resolution of 3 nm,and an F number of 3.5 which has a spectral curvature of less than 2μm and a spectral line curvature of less than 2μm.The optical system has a diffuse spot radius of less than 5.4μm in the wavelength range of 400~800 nm,and can distinguish slit images with a spectral interval of 2 nm.The energy concentration of all fields of view can reach 90%in the 2×2 pixel scale.The design results show that the use of curved slit and distortion of the collimator lens and focusing lens can effectively correct the curve of the spectral line,which has important guiding significance for the design of the coaxial PGP imaging spectrometers.In this article,we calculated the optimal slit shape and lens parameters for different slit lengths and different grating parameters,which proved that the method had universal applicability.