Since the 1990’s, practical THz/mmw imaging for terrestrial applications, particularly for security screening, has advanced far beyond the first primitive adaptations of astronomical detectors, and is now nearly an industrial reality. The greatest hurdles have been and remain imaging speed and pixel count, as many applications require near real-time (i.e. 30 frame/sec) acquisition with >10 kilopixel image formats. I will compare the operating principles and review the current capabilities of the main detector types amenable to incorporation into imaging array formats, viz. uncooled and cryogenic microbolometers, zero-bias and other direct-detection diodes, and coherent receivers, either with mixer or low-noise amplifier front ends. These vary in their suitability for active and passive imaging at various THz frequencies, while the choice between active and passive modes is largely based on phenomenology, specifically the balance between specular and diffuse scattering in the scenes being imaged. This is all illustrated in still images, videos, and detector measurements obtained in our lab over several years.
Dr. Erich Grossman, (A.B. magna cum laude, Harvard, 1980) received his Ph.D. in physics, from the California Institute of Technology in 1987, for thesis work developing an ultra-low noise, heterodyne receiver for 2 THz astronomy. From 1988 to 1989, he was a postdoctoral fellow at the Univ. of Texas at Austin, and in 1989, he joined the National Institute of Standards and Technology, Boulder, CO, where he is now a physicist in the Optoelectronics Division. His work at NIST focuses on infrared and submillimeter system development. Notable accomplishments include the development and demonstration of the world's highest frequency, high efficiency lithographic antennas, the world's highest frequency Josephson junctions, (awarded a Dept. of Commerce Gold Medal in 1993), and conception and early development of the SQUID multiplexer, first enabling large monolithic arrays of superconducting detectors. More recently, he has developed several 0.1-1 THz cameras for security applications. He is chair of the Metrology Working Group for the DARPA Terahertz Electronics program, and received the 2010 Allen V. Astin Measurement Science Award. He is also adjunct professor of electrical engineering at the Univ. of Colorado.