| Imaging spectrometer is capable of acquiring geometrical figure and spectral featureof targets by which their type are recognized and their material composition is identified.It has been widely used in precision agriculture, industrial machine vision, aerospaceremote sensing and other fields. Spectroscopic imaging optics is its core part and sodefinitively impacts on its performance. Since Littrow-Offner spectroscopic imagingsystem with a convex diffraction grating as its dispersion component is concentric, itinherits both the Offner mount advantages of low inherent aberration, high image quality,high speed and powerful light collection, and the Littrow mount ones of simple andcompactness. It is in accordance with the tendency of current imaging spectrometers withthe requirement of high resolution and small size at the same time.In this paper, the structure and working principle of Littrow-Offner spectroscopicimaging system were introduced firstly. Its imaging characteristic was theoreticallyanalyzed. Then through investigation of its astigmatism with Young’s formulas abouthorizontal and sagittal imaging, it was shown that the Littrow-Offner mount existinherently positive astigmatism. Hereby, a meniscus singlet with negative astigmatismwas introduced to cancel out the inherently positive. Under the condition that theintegration of astigmatism over its operating wavelength range minimizes, the way todetermine its initial structure parameters was given. Secondly, take Raman imagingspectrometer for example, its initial structure was determined based on here developedtheoretical analysis, and its compact spectroscopic imaging system with single slit wasoptimally designed. In order to extend its working wavelength range, anotherspectroscopic imaging system with double slits was designed. Take spaceborne imaging spectrometers suitable for remote sensing detection of atmospheric trace gas carbondioxide for another example, three spectroscopic imaging systems with very high spectralresolution of over0.03nm were optimized, which covers respectively O2-A, weak CO2and strong CO2band amongst wavelength of0.758to2.085m. Finally, as arepresentative illustration, its tolerance scheme that facilitates its manufacture andalignment is obtained through detail analysis and optimization. |
