Characterization and use of an acousto-optic tunable filter for hyperspectral remote sensing

This study reports the characterization of a noncollinear Tl₃AsSe₃ acousto-optic tunable filter (AOTF) for use in an 8 to 12 micron hyperspectral imaging system. Electronic testing was performed to determine the filter\u27s resonance points and the variations in impedance as a function of the acoustic frequency. The dependence of the filter\u27s diffraction efficiency on the applied voltage, frequency, and dissipated power in the crystal was determined. Bandwidth measurements of the diffracted beam were performed using an FT-IR, and found to be independent over the range of applied power introduced into the filter. After characterization, the AOTF was placed in an optical system designed to gather light from a distant object, collimate a beam, pass the beam through the AOTF, and reform an image onto the array of an infrared camera. This optical system was then used to collect images of a remote sample cell containing dimethyl methyl phosphonate at elevated temperatures. Several wavelengths were selected on- and off-peak for three absorbance peaks. These images were collected for five different DMMP concentrations and calibration curves were calculated. The potential problem of wavelength jumping, where changing wavelength moves the diffracted beam spatially, was also analyzed. This is believed to be the first demonstration of an AOTF-based remote sensor for detection of militarily significant compounds --Abstract, page iv