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The computed tomography imaging spectrometer (CTIS) is a snapshot (i.e. non-scanning) imaging spectrometer conceived separately by Takayuki Okamoto and Ichirou Yamaguchi at Riken (Japan), and by F. Bulygin and G. Vishnakov in Moscow (Russia). The concept was subsequently further developed by Michael Descour, at the time a PhD student at the University of Arizona, under the direction of Prof. Eustace Dereniak.
The optical layout of a CTIS instrument is shown at right: a field stop is placed at the image plane of an objective lens, after which a lens collimates the light before it passes through a disperser (such as a grating or prism). Finally, a re-imaging lens maps the dispersed image of the field stop onto a large-format detector array. Shown here is an example in which the device is imaging the university of Arizona's logo, uses a kinoform grating to disperse the transmitted light, and measures a 3 × 3 dispersion pattern on the detector array. After measurement, an algorithm is used to convert the multiplexed (overlapped) two-dimensional data into the three-dimensional datacube (spectrally resolved image). Conceptually, one can consider each of the dispersed images on the detector as a 2D projection of the 3D datacube, in a manner analogous to the way in which X-ray projections measured by medical computed tomography instruments are used to estimate the 3D volume distribution within a patient's body.