Non-scanning dual infrared band hyperspectral imaging spectrometer design

Abstract

Recent advances in dual band infrared focal plane technology now enable the design and testing of a dual infrared band snapshot imaging spectrometer, the first-ever of its kind. A review of proof of concept results from a dual-visible-band Computed Tomographic Imaging Spectrometer (CTIS) system is presented. The dual-visible system demonstrates that it is possible to reconstruct two spatially co-registered hyperspectral data cubes covering different spectral bands. Based on the visible band CTIS proof of concept, a similar infrared system is now proposed. Critical to the CTIS system is the design of the Computer Generated Holographic (CGH) disperser. Several different (CGH) designs are considered. A first order optical design for the dual infrared band CTIS is presented.Keywords: Dual band, imaging spectrometer, computed tomographic imaging spectrometer BACKGROUND:The recent advances in infrared focal plane technology and the increase in computing power have enabled the creation of a snapshot dual infrared band imaging spectrometer. Infrared focal planes are now being designed and built that consist of detectors that are sensitive to two different spectral regions stacked on top of each other. The advances in computing power have enabled the development of the Computed Tomographic Imaging Spectrometer (CTIS). The CTIS system uses a Computer Generated Holographic (CGH) dispersive optical element to disperse the spectral content of the scene.The goal of all imaging spectrometers is to obtain the spatially registered spectral content of the scene of interest. The product of an imaging spectrometer is a three dimensional data cube. Two of the dimensions of the data cube are the x and y spatial coordinates while the third coordinate is the wavelength of the light intensity in the scene. Conventional imaging spectrometers scan the scene either spatially like a whiskbroom or pushbroom system or spectrally like a filter wheel system. For dynamic scenes the scanning imaging spectrometers may not be able to complete the scan, whether spatially or spectrally, before the scene significantly changes. The CTIS system on the other hand obtains all the information required to reconstruct a data cube in a single snapshot. The spectral content of the scene is dispersed in several radial directions. Each diffracted order is a two dimensional projection of the data cube. The data cube is reconstructed by using tomographic techniques similar to those used in medical computed tomography. Within the data cube we define the discrete three-dimensional differential volume element as a voxel.There are times when we may need to measure the hyperspectral content of the scene over two separate bands. It is possible to split the incoming light in two and reconstruct the two data cubes measured by separated HSI channels independently. The challenge then becomes spatial co-registration of the two cubes. If the focal plane consists of detectors sensitive to the two bands in an interwoven pattern (similar to the commercial approach for three waveb...

Hyperspectral opportunities with next-generation QSIP arrays

“…The CGH also has the properties of multiple grating orders. A dualband CTIS design, employing a dualband focal plane sensitive to the MWIR and LWIR, has been considered [3,4].…”