<title>Progress in AOTF hyperspectral imagers</title>

Performance characterization of VNIR and SWIR spectropolarimetric imagers

“…An imager designed using an AOTF is ideally suited to provide both agile spectral and polarization signatures. [1][2][3][4][5][10][11][12] At the U.S. Army Research Laboratory (ARL), we have developed small, vibration-insensitive, robust and programmable hyperspectral imagers covering the spectral regions from the UV to the LWIR. [1][2][3][4][5][13][14][15][16][17][18][19][20] Such imagers require minimum amount of data processing because they can collect data at only select wavelengths of interest and the selected wavelengths can be changed based on the scenes of interest.…”

“…These include use of a diffractive optics lens or element, 6 a Fabry-Perot etalon, 7 a Michelson interferometer, 8 a liquid crystal tunable filter (LCTF), 9 or an acousto-optic tunable filter (AOTF). [1][2][3][4][5][10][11][12] We chose use of an AOTF because it is a solid-state device with no-moving-parts instead of a diffractive-optic lens, a Fabry-Perot etalon, or a Michelson interferometer, each of these requires moving parts and hence is sensitive to vibrations. Both an AOTF and an LCTF are polarization sensitive tunable filters.…”

“…We developed a compact hyperspectral/polarization imager that provides each spectral image with two linear incident polarizations using an acousto-optic tunable filter (AOTF) in combination with a voltage-controlled liquid crystal variable retarder (LCVR) and investigated development of different types of spectropolarimetric imagers with AOTFs. [1][2][3][4] We also developed a full Stokes polarization imager using an AOTF with two LCVRs. 5 Recently, we developed two separate spectropolarimetric imagers, one operating in the visible-near-infrared (VNIR) spectral region from 450 to 800 nm and the second in the shortwave-infrared (SWIR) region from 1000 to 1600 nm.…”

“…At ARL, we have developed a number of different AOTF based hyperspectral imagers using a number of different noncollinear AOTFs fabricated in different birefringent crystals with different cameras to cover the wavelength regions from the UV to the LWIR. We use a KDP or MgF2 AOTF with an extended range response Si charge-coupled-device (CCD) camera to cover the deep UV to the visible region, 13,14 a TeO2 AOTF with an off-the-shelf Si CCD camera to cover the VNIR region from 400 to 800 nm, 1 a TeO2 AOTF to cover the SWIR region from 900 to 1700 nm with a room temperature InGaAs camera, 3,16 another TeO2 AOTF with a liquid nitrogen-cooled InSb camera to cover the mid wave IR (MWIR) region from 2 to 4.5 µm, 15,16 and a TAS (thallium arsenic selenide), 17,18 or Te (tellurium) 19 AOTF with a liquid nitrogen-cooled HgCdTe camera to cover the LWIR region. We have also developed mercurous halide crystals that can be used over 0.35 to 30 µm.…”

Materials for imaging acousto-optic tunable filters

“…At ARL, we have developed prototype AOTF-based hyperspectral imagers operating in the UV, the visible to near-infrared (VNIR), the SWIR, the MWIR, and the LWIR . Noncollinear AOTFs were used in these hyperspectral imagers based on using single crystals of potassium dihydrophosphate (KDP), 7-9 magnesium fluoride (MgF 2 ), 10 tellurium dioxide (TeO 2 ), [11][12][13][14][15][16][17][18][19][20][21][22] thallium arsenic selenide (Tl 3 AsSe 3 or TAS), [22][23][24] tellurium (Te) [25][26][27][28] and mercurous bromide (Hg 2 Br 2 ). [29][30][31][32][33] The most commonly used AOTF crystal is TeO 2 .…”