Originating Technology/NASA Contribution
Since its founding in 1958, NASA has pioneered the use of different frequencies on the electromagnetic spectrum—including X-ray, microwave, and infrared wavelengths—to gather information about distant celestial bodies. During the 1962 Mariner 2 mission, NASA used microwave radiometers that operated in the range of 15–23 gigahertz (GHz) to assess the surface temperature of Venus and to determine the percentage of water vapor in its atmosphere.
Today, there is another area on the spectrum proving uniquely useful to scientists: the terahertz (THz) range, spanning from about 100 GHz–10,000 GHz. (1 THz equals approximately 1,000 GHz.) Terahertz frequencies span the lesser-known gap on the electromagnetic spectrum between microwave radiation and infrared (and visible) light, falling within the spectral range where most simple molecules resonate. This molecular resonance makes terahertz particularly useful for chemical spectroscopy and the remote sensing of specific molecules. In the 1990s, NASA began using frequencies above 300 GHz (more than an order of magnitude higher than the instrumentation on Mariner 2) to perform spectral analysis of molecular clouds and planetary atmospheres. Instruments using these higher frequencies have included the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS), deployed from 1991–2001, and the Microwave Instrument for the Rosetta Orbiter (MIRO), launched in 2004. With UARS-MLS, NASA used advanced terahertz receivers to measure the emission signatures from atmospheric molecules, providing researchers with valuable data about the changes in the Earth’s protective ozone layer. MIRO, set to rendezvous with the comet 67P Churyumov-Gerasimenko in 2014, will use terahertz instrumentation to analyze the comet’s dust and gasses.
Although NASA has been a driving force behind the development of terahertz technology, scientific equipment for terahertz research—including transmitters, receivers, and basic test and measurement equipment—is not widely available, making scientific experiments in this range between traditional electronics and quantum photonics more costly and greatly limiting commercial development in the field. Given NASA’s interest in studying distant bodies in space as well as in improving life on Earth, the Agency has collaborated with private industry to develop terahertz technologies.
In the early 1980s, University of Virginia professor Thomas Crowe and research scientist William Bishop worked with NASA to develop high-frequency diodes for UARS-MLS instrumentation. In 1996, Bishop and Crowe founded Virginia Diodes Inc. (VDI), based in Charlottesville, Virginia. A few years later, the company began developing and selling terahertz components and subsystems, with a mission to make the terahertz region of the electromagnetic spectrum as useful for scientific, military, and commercial applications as the microwave and infrared frequency bands have become.