The Infrared Retina: Bioinspired Sensing Using Nanoscale Superlattices and Quantum Dots
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Dr. Sanjay Krishna is Professor, Department of Electrical and Computer Engineering; Associate Director, Center for High Technology Materials, University of New Mexico. Lecture presented Sept. 8, 2011. Infrared detectors operating in the 3-20 mm are important due to three main reasons. Firstly, the atmosphere is transparent in the two bands referred to as mid-wave infrared (MWIR, 3-5 mm) and long-wave infrared (8-12 mm), making it possible to see through fog and smoke under poor visibility conditions. Secondly, a lot of chemical species have characteristic absorption features in this wavelength range, making these detectors vital for remote sensing and stand-off detection. Finally, there is blackbody emission from living objects at these wavelengths, making it possible to use them for “night vision” and thermography applications such as surveillance and medical diagnostics. Presently, we are in what is referred to as the third generation of infrared detectors. The first generation of infrared detectors was based on single pixel and linear detector arrays. The second generation consisted of small format staring focal plane arrays. The emphasis of the third generation imagers is on (i) higher operating temperature, (ii) multicolor tunability and (iii) large format arrays. In this talk, I will try and look into the crystal ball to make predictions about the fourth generation of infrared detectors. Using the concept of a bioinspired infrared retina, I will make a case for an enhanced functionality in the pixel. The key idea is to engineer the pixel such that it not only has the ability to sense multimodal data such as color, polarization, dynamic range and phase but also the intelligence to transmit a reduced data set to the central processing unit. I will use two material systems, which are emerging as promising infrared detector technologies as prototypes to highlight this approach. These are (i) InAs/InGaAs self assembled quantum dots in well hetereostructure and InAs/(In,Ga)Sb strain layer superlattices (SLS) Detectors. Various approaches for realizing the infrared retina, such as plasmonic resonators[i], will be discussed. In addition to the applications of infrared imaging for defense application, I will highlight the role of infrared imaging in noninvasive medical diagnostics. In particular, I will highlight some work on using infrared imaging in the early detection of skin cancer. [i] S.J. Lee et al., Nature Communications, 2: 286 April 2011
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