IERUS Technologies investigated the feasibility of developing a high resolution, passive MWIR polarimetric imaging system for both day and night operation at short (1 – 5 meters) and long (1 – 2 km) range operation. The sensor system used a micro-polarizer array (MPA) over the focal plane array (FPA) in order to capture four channels of polarimetric information simultaneously. It also used an optical registration array (ORA) over the MPA in order to spatially register the polarimetric information. The MPA-ORA device is integral to the FPA, forming a drop-in-replacement, saving system size and weight relative to other polarimetric imaging technologies. A system was designed for a prototype that mitigates risk and demonstrates the utility of the ORA. The FPA employed is a MWIR array with a reticulated detector array which reduces electrical pixel-to-pixel crosstalk to zero. Polarization and radiometric performance predictions of the design will be presented.
Single resonance chemical remote sensing, such as Fourier-transform infrared spectroscopy, has limited recognition
specificity because of atmospheric pressure broadening. Active interrogation techniques promise much greater
chemical recognition that can overcome the limits imposed by atmospheric pressure broadening. Here we introduce
infrared - terahertz (IR/THz) double resonance spectroscopy as an active means of chemical remote sensing that
retains recognition specificity through rare, molecule-unique coincidences between IR molecular absorption and a
line-tunable CO2 excitation laser. The laser-induced double resonance is observed as a modulated THz spectrum
monitored by a THz transceiver. As an example, our analysis indicates that a 1 ppm cloud of CH3F 100 m thick can
be detected at distances up to 1 km using this technique.
Laser induced Semiconductor Switches (LSS), comprised of a gap antenna deposited on a semiconductor substrate and
photoexcited by a pulsed laser, are the primary source of THz radiation utilized in time-domain spectroscopy (TDS).
THz-TDS applications such as standoff detection and imaging would greatly benefit from greater amounts of power
coupled into free space radiation from these sources. The most common LSS device is based on low temperature-grown
(LT) GaAs photoexcited by Ti:sapphire lasers, but its power performance is fundamentally limited by low breakdown
voltage. By contrast, wide band-gap semiconductor-based LSS devices have much higher breakdown voltage and could
provide higher radiant power efficiency but must be photoexcited blue or ultraviolet pulsed lasers. Here we report an
experimental and theoretical study of 10 wide band-gap semiconductor LSS host materials: traditional semiconductors
GaN, SiC, and ZnO, both pristine and with various dopants and alloys, including ternary and quaternary materials
MgZnO and InGaZnO. The objective of this study was to identify the wide bandgap hosts with the greatest promise for
LSS devices and compare their performance with LT-GaAs. From this effort three materials, Fe:GaN, MgZnO and
Te:ZnO, were identified as having great potential as LSS devices because of their band-gap coincidence with frequency
multiplied Ti:Sapphire lasers, increased thermal conductivity and higher breakdown voltage compared to LT-GaAs, as
well as picoseconds scale recombination times.
Deployable polarimetric imaging systems often use 2×2 arrays of linear polarizers at the pixel level to measure the
polarimetric signature. This architecture is referred to as a micro-grid polarizer array (MPA). MPAs are either bonded to
or fabricated directly upon focal plane arrays. A key challenge to obtaining polarimetric measurements of sub-pixel
targets using MPAs is registering the signals from each of the independent channels. Digital Fusion Solutions, Inc has
developed a micro-optic approach to register the fields of view of 2x2 subarrays of pixels and incorporated the device
into the design of a polarimetric imager. Results of the design will be presented.