Spectrally Adaptive Nanoscale Quantum Dot Sensors

The potential use of nanotechnology for hyperspectral (HS) and multispectral (MS) sensing and imaging is described in this article. It is noted how HS and MS sensors/imagers have great potential for a variety of applications important to the intelligence community; such applications range from monitoring chemical agent production to identifying geographical terrain. It is also noted that, by sensing the spectrum of reflectance/transmittance of the agents in different wavelength bands—as can be done with HS/MS systems—image analysis capability and detection probability can be greatly improved. However, traditional MS/HS systems are fairly bulky and expensive. The work described concerns advances in nanotechnology, which offer potential solutions to these drawbacks. In particular, the creation of spectrally adaptive focal plane arrays, based upon nanoscale quantum dots (QDs) in the midinfrared regime (3–14 µm), hold promise of producing compact and relatively inexpensive systems. Such sensors use electro-optics and, thus, do not involve moving parts. The spectral adaptability is mainly attributed to the quantum-confined Stark effect that results from the QDs being placed in asymmetrical quantum potential wells. As a result, QD detectors can sense information over different spectrally overlapping bands as the electrical bias applied across the detector is judiciously varied. Signal-processing-based algorithms are then developed and utilized to maximally exploit the bias-dependent and diverse spectral response of the QD detectors for the purpose of target-spectrum reconstruction and target classification. Examples of these applications are also given in this article. Keywords: quantum dots; infrared detector; DWELL; spectral tuning; algorithmic spectrometer; feature selection