Infrared spectral features have proved useful in the identification of threat objects. Dual-band focal-plane arrays (FPAs) have been developed in which each pixel consists of superimposed midwave and long-wave photodetectors [Dyer and Tidrow, Conference on Infrared Detectors and Focal Plane Arrays (SPIE, Bellingham, Wash., 1999), pp. 434-440]. Combining dual-band FPAs with imaging spectrometers capable of interband hyperspectral resolution greatly improves spatial target discrimination. The computed-tomography imaging spectrometer (CTIS) [Descour and Dereniak, Appl. Opt. 34, 4817-4826 (1995)] has proved effective in producing hyperspectral images in a single spectral region. Coupling the CTIS with a dual-band detector can produce two hyperspectral data cubes simultaneously. We describe the design of two-dimensional, surface-relief, computer-generated hologram dispersers that permit image information in these two bands simultaneously.
We observe polarization-resolved coherent beam combination through nondegenerate two-wave mixing in water-glycerol suspensions of shaped polytetrafluoroethylene microparticles. Coherent energy transfer that arises from translational and orientational moving index gratings was observed. A theory for beam combination through nondegenerate two-wave mixing is presented and found to be in excellent agreement with these measurements.
Abundances of material components in objects are usually computed using techniques such as linear spectral unmixing on individual pixels captured on hyperspectral imaging devices. However, algorithms such as unmixing have many flaws, some due to implementation, and others due to improper choices of the spectral library used in the unmixing (as well as classification). There may exist other methods for extraction of this hyperspectral abundance information. We propose the development of spatial ground truth data from which various unmixing algorithm analyses can be evaluated. This may be done by implementing a three-dimensional hyperpspectral discrete wavelet transform (HSDWT) with a low-complexity lifting method using the Haar basis. Spectral unmixing, or similar algorithms can then be evaluated, and their effectiveness can be measured by how well or poorly the spatial and spectral characteristics of the target are reproduced at full resolution (which becomes single object classification by pixel).
The recent development of channelled spectropolarimetry presents opportunities for spectropolarimetric measurements of dynamic phenomena in a very compact instrument. We present measurements of stress-induced birefringence in a simple plastic by both a reference rotating-compensator spectropolarimeter and a channelled spectropolarimeter. The agreement between the two instruments shows the promise of the channelled technique and provides a proof-of-principle that the method can be used for a very simple conversion of imaging spectrometers into imaging spectropolarimeters.
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