Method for designing a grid-slit spectrometer with low spectral-line bending

Abstract

The classic single-slit spectrometer exhibits low field utilisation in the direction of the slit width and requires a push-broom observation method to visualise moving point targets. Therefore, we designed a spectrometer with a grid slit to overcome these limitations. First, a grid slit composed of two sets of vertically arranged slit arrays, each containing five slits, was established. Then, the spectral-line bending of the off-axis slits was analysed, and the parameters of the dispersive elements that minimised the spectral-line bending of the slit arrays were selected as the initial values. Next, a merit function was established to consider the systematic distortion, and finally, the system was optimised. The proposed spectrometer design enabled a grid slit with 10 slits to be implemented, which significantly enhanced the field utilisation of the spectrometer and enabled starting-observation-mode operation. The spectral-line bending of each slit was less than 0.21 μm (less than one-third of a pixel size) and the modulation transfer function was higher than 0.7 (@45.45 lp/mm). The design and analysis results confirmed the feasibility of the proposed grid-slit design method, which can potentially be applied to other spectrometers to improve their field utilisation or to enable starting-observation-mode operations.