From Event: SPIE Optical Engineering + Applications, 2016
The Littrow form of spectrograph has a long and storied history in astronomical spectroscopy since its presentation in 1862 by Otto von Littrow. Light from an input slit traverses the same optical elements in reaching the dispersing element (prism or grating) and returning to a focused, dispersed image at the focal plane. This 1:1 symmetry helps cancel aberrations in the reimaging optics while presenting the dispersing element with the geometry most favorable to dispersion, efficiency and anamorphic scale change. Historically, Littrow spectrographs have not been pushed to high throughputs (fast f/ratios). However in the short- and mid-wave infrared particularly, high index, low dispersion materials like silicon and germanium can be combined effectively into compact, high throughput (<f/2.5), well corrected 1:1 reimaging systems that economize volume and cooling resources and are well-suited for moderately high resolution spectrographic space missions such as atmospheric sounders. We present some high throughput Littrow spectrograph concepts designed for infrared atmospheric sounding missions and incorporating both plane and immersion gratings.
David W. Warren and Sara Lampen, "Littrow spectrographs for moderate resolution infrared applications," Proc. SPIE 9976, Imaging Spectrometry XXI, 997606 (Presented at SPIE Optical Engineering + Applications: August 29, 2016; Published: 19 September 2016); https://doi.org/10.1117/12.2239224.
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