Relatively inexpensive terahertz imaging

The advantages of imaging at terahertz [THz] frequencies are well known for homeland security applications. It is possible to image through non-highly conducting media, and there is no known biological hazard. Thus, it is possible to image concealed weapons and explosives. There are also many biomedical applications of THz radiation. One problem limiting widespread use is the expense of such equipment, much of which revolves around the detector. One solution is the use of miniature neon indicator lamps as detectors. Such devices cost about 30 cents each, and certain models exhibit noise equivalent powers to terahertz radiation similar to those of Golay cells and bolometers. These miniature lamps are biased to an abnormal glow discharge, and illumination with THz radiation increases the discharge current.2 In practical use, the THz radiation is amplitude modulated, and the neon glow discharge detector [GDD] detects the THz modulation envelope. Internal signal amplification on the order of a million can arise through ionizing collisions of signal electrons with neutral gas atoms. The low price of GDD lamps, the electronic ruggedness, and their THz sensitivity make them an attractive choice as detectors for novel focal plane array THz cameras.3 Indeed, such devices are currently under development. Preliminary images using 4×4 GDD arrays at 100 GHz have already been obtained. VLSI boards for a small array are being built for imaging at 300 GHz, and further development to 64×64 arrays is being planned. Image processing to improve THz image quality is also planned.