Design of a compact wide-band triple grating imaging spectrometer based on freeform surfaces

Wide-band, high spectral resolution, and miniaturized imaging spectrometers have important applications. However, the working band, spectral resolution, and volume of the imaging spectrometers are mutually restricted. To solve this problem, we proposed a method in which multiple working bands share the same optical components except gratings, and the working bands switch with the switching of the working gratings. Based on the freeform surfaces characterized by X Y polynomials, we designed a compact wide-band triple grating imaging spectrometer through the design ideas of human-computer interaction and iterative optimization. The imaging spectrometer works in the wavelength band of 200nm∼1600nm, covering ultraviolet (UV), visible, and near-infrared light, and it has a compact optical path volume of 24mm×38mm×80mm. Three gratings with 0.0025 mm, 0.005 mm, and 0.01 mm line spacing are used to realize dispersion with high diffraction efficiency in the bands of 200nm∼400nm, 400nm∼800nm, and 800nm∼1600nm, respectively. The UV detector receives imaging light in the UV band (200nm∼400nm), and the visible near-infrared (VNIR) detector receives imaging light in the visible and near-infrared bands (400nm∼1600nm). The design results show that the spectral resolutions of the three bands are 0.4 nm, 0.8 nm, and 1.6 nm, and the spectral smile and keystone distortion are less than 1.4 µm. The design results have engineering application value.