消谱线弯曲PGP型成像光谱仪系统设计

Design of PGP imaging spectrometer with eliminating spectral line bending

针对棱镜-光栅-棱镜(PGP)型成像光谱仪谱线弯曲(Smile)难校正的问题,提出了一种利用狭缝离轴和减小第一块棱镜顶角,再结合会聚镜畸变校正PGP型光谱仪谱线弯曲的方法。该方法在保留了PGP型光谱仪的布拉格(Bragg)衍射和系统共轴等优点的基础上,校正了光谱仪的谱线弯曲和色畸变(Keystone)。在相同的技术指标下,对传统型和改进型PGP模型做了谱线弯曲对比。为了验证该方法的可行性,设计了一款光谱分辨率为2.8 nm的光谱仪,点列图均方根(RMS)半径小于8μm,满足成像质量要求,Smile为1.50μm、Keystone为3.52μm,均小于0.2倍像素。设计结果表明,通过减小棱镜顶角校正中心波长的Smile,利用狭缝离轴实现光谱仪系统共轴,利用会聚镜畸变校正剩余波长的Smile可以有效校正PGP型光谱仪的谱线弯曲。

A method was put forward to eliminate spectral line bending(Smile)of Prism-Grating-Prism(PGP)spectrometer by reducing the vertex angle of the first prism and combining with off-axis slit and the distortion of convergent lens.The method could be used to retain the Bragg diffraction and coaxial characteristic of the PGP spectrometer and eliminate spectral line bending and spectral Keystone of the spectrometer.The Smile of the traditional PGP model and the improved PGP model with the same technical indexes were compared.In order to verify the feasibility of the method,a spectrometer with a spectral resolution of 2.8 nm was designed.The root mean square(RMS)of the spot radius was less than 8μm,both imaging quality and design index requirements could be satisfied.The Smile and Keystone of the system were 1.50μm and 3.52μm respectively,which were both less than 0.2 pixel.The design result indicates that the Smile and Keystone of the PGP spectrometer can be effectively eliminated by reducing the vertex Angle of the prism to eliminate the Smile of the center wavelength,using the slit off axis to retain coaxial characteristic of the PGP spectrometer,using the distortion of convergent lens to eliminate the Smile and Keystone of the remaining wavelength.