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The advantages of terahertz (THz) imaging are well known. They penetrate well most
non-conducting media and there are no known biological hazards, This makes such
imaging systems important for homeland security, as they can be used to image
concealed objects and often into rooms or buildings from the outside. There are also
biomedical applications that are arising. Unfortunately, THz imaging is quite
expensive, especially for real time systems, largely because of the price of the
detector. Bolometers and pyroelectric detectors can each easily cost at least hundreds
of dollars if not more, thus making focal plane arrays of them quite expensive.
We have found that common miniature commercial neon indicator lamps costing
typically about 30 cents each exhibit high sensitivity to THz radiation [1-3], with
microsecond order rise times, thus making them excellent candidates for such focal
plane arrays. NEP is on the order of 10-10 W/Hz1/2. Significant improvement of
detection performance is expected when heterodyne detection is used
Efforts are being made to develop focal plane array imagers using such devices at 300
GHz. Indeed, preliminary images using 4x4 arrays have already been obtained. An
8x8 VLSI board has been developed and is presently being tested. Since no similar
imaging systems have been developed previously, there are many new problems to be
solved with such a novel and unconventional imaging system.
These devices act as square law detectors, with detected signal proportional to THz
power. This allows them to act as mixers in heterodyne detection, thus allowing NEP
to be reduced further by almost two orders of magnitude.
Plans are to expand the arrays to larger sizes, and to employ super resolution
techniques to improve image quality beyond that ordinarily obtainable at THz
frequencies.
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