Diffraction-limited Littrow imaging grating spectrometer for the New Vacuum Solar Telescope

Abstract

To observe fine structures on the Sun and study the thermodynamic properties of the solar atmosphere with different height distributions, a diffraction-limited imaging grating spectrometer with high spectral resolution is an essential tool. However, its imaging performance will be limited by wavefront aberration caused by atmospheric turbulence and static wavefront aberration. In order to compensate the aberrations and lower the manufacturing precision of the optical element, an aberration correction method for a diffraction-limited Littrow imaging grating spectrometer (DLIGS) based on adaptive optics is proposed. To correctly detect the static aberration, the calibration system is adopted. To validate the method, a prototype for the New Vacuum Solar Telescope is developed. The results demonstrate that the proposed method is feasible, and near diffraction-limited imaging performance is achieved after the adaptive optics correction. The real spectral resolution of the prototype is roughly 6 pm, which is close to the numerical result (5.6 pm).