基于传统罗兰圆结构的凹面光栅成像光谱仪,尽管具有很好的轴上点成像特性,但是存在较大的光栅离轴像差,离轴性能显著降低,不适用于大离轴视场、宽波段的空间和光谱成像。因此,基于超环面变线距光栅工作在非罗兰圆结构下的像差校正理论,设计了一款兼具大离轴视场和宽波段的太阳极紫外正入射成像光谱仪,使用三个平场探测器,可实现在极紫外波段对包括日冕和过渡区域在内的太阳上层大气的高空间和高光谱分辨观测。该仪器仅有两次反射表面,同时使用周期性的SiC/Al多层镀膜最大化地减小了极紫外波段的光子通量损失,提高了仪器的传输效率。该成像光谱仪的工作波段为40~47 nm、53~60 nm和66~73 nm,口径为100 mm,沿狭缝方向的离轴视场为18',系统的空间分辨率优于0.55″,光谱分辨率优于30×10 -4 nm。

Concave grating imaging spectrometers operating at conventional Rowland circle mounting have excellent on-axis imaging performances. However, such spectrometers have been found to possess poor off-axis imaging performances as a result of the existence of large off-axis grating aberrations, which are not suitable for spatial and spectral imaging under a large off-axis field of view (FOV) and a broad band. Based on the aberration correction theory of toroidal varied line-space gratings operating at non-Rowland circle mounting, we designed a solar extreme ultraviolet (EUV) normal-incidence imaging spectrometer with a large off-axis FOV and a broad band. Specifically, this instrument can provide excellent imaging with high spatial and spectral resolutions for EUV spectroscopic observations of the solar corona and transition region. Besides, the instrument has only two reflective surfaces with periodic SiC/Al multilayer coating, which minimizes the loss of photon flux in the EUV band and improves the transmission efficiency of the instrument greatly. Finally, this unprecedented spectrometer, with an aperture of 100 mm and the operating bands of 40-47 nm, 53-60 nm, and 66-73 nm, achieves a spatial resolution and a spectral resolution better than 0.55″ and 30×10 ^-4 nm respectively, providing ultrahigh resolution imaging over the off-axis FOV of 18' along the slit.