CIEMAS 2531

Fitzpatrick Institute for Photonics

Duke University

Durham NC 27705

(919) 660.5599

Spectral imagers measure a 3D datacube of information which consists of 2D spatial information that is captured by an ordinary camera complemented with 1D spectral information at each pixel. Traditionally, a spectral image is captured using some form of temporal scanning to gradually build up the 3D datacube of information about the scene.

CASSI instruments are a new class of snapshot spectral imagers that rely on a combination of aperture coding and compressed sensing theory. Aperture coding is used to decipher a coded spectral/spatio-spectral 2D projection of the 3D datacube. Compressed sensing theory is used because Dirac sampling of every element is wasteful, as it ignores correlations between spatial and spectral elements of the datacube. The theory says that if a signal of interest is sparse in some basis other than the Dirac sampling basis, then we can get away with making relatively few observations of the signal to recover the most significant non-zero components of the signal in that other basis. This means that we can recover an accurate estimate of the 3D datacube from a 2D set of measurements.

A comparison of the dual disperser and single disperser CASSI instruments is made here:

http://www.disp.duke.edu/projects/CASSI/index.ptml

Associated publications:

A paper on a CASSI instrument with a dual disperser architecture has been published in Optics Express:

Gehm et al. "Single-shot compressive spectral imaging with a dual-disperser architecture.", Optics Express, 15(21), 2007.

Papers on the SD-CASSI instrument:

1. Wagadarikar et al. "Single disperser design for compressive, single-snapshot spectral imaging", Proc. SPIE Vol. 6714, 2007.

2. Wagadarikar et al. "Single disperser design for coded aperture snapshot spectral imaging," feature issue on Computational Optical Sensing and Imaging, Applied Optics 47 (10), B44-51 (2008)

3. Wagadarikar et al. "Video rate spectral imaging using a coded aperture snapshot spectral imager," Optics Express, 17(8), 2009.

Please feel free to e-mail me if you have any more questions.

Coded aperture snapshot spectrometer

Our coded aperture spectrometer is able to maintain equivalent spectral resolution to a slit spectrometer, while having dramatically higher throughput. In the instrument, the entrance slit of a traditional spectrometer is replaced with a much wider, coded aperture mask. In a snapshot, the detector measures a convolution of the spectrum incident on the mask and the aperture code. Post-processing of the detector data is needed to recover the spectrum.

(Left) Spectra reconstructed with slit at increasing exposure times. (Right) Spectra reconstructed with coded aperture at increasing exposure times. The coded aperture makes the spectrometer considerably more sensitive to the spectral peaks of Xenon in the spectral range of the instrument.

I gratefully acknowledge partial funding of my research by a Postgraduate doctoral Scholarship from the Natural Sciences and Engineering Research Council of Canada (NSERC).