History
History of the THz Science & Technology Network
The THz Science & Technology Network was primarily born as a result of a DOE / NSF / NIH sponsored Workshop on Opportunities in Terahertz (THz) Science held February 12–14, 2004. Below is the abstract of the Workshop Report, and you can download the Full Report (10 Mb PDF).
Abstract
DOE-NSF-NIH Workshop on Opportunities in THz Science
This report is based on a Workshop on Opportunities in Terahertz (THz) Science held February 12–14, 2004, to discuss basic research problems that can be answered using THz radiation. The workshop did not focus on the wide range of potential applications of THz radiation in engineering, defense and homeland security, or the commercial and government sectors of the economy. The workshop was jointly sponsored by DOE, NSF, and NIH.
The region of the electromagnetic spectrum from 0.3 to 20 THz (10– 600 cm-1, 1 mm – 15 µm wavelength) is a frontier area for research in physics, chemistry, biology, medicine, and materials sciences. Sources of high quality radiation in this area have been scarce, but this gap has recently begun to be filled by a wide range of new technologies. Terahertz radiation is now available in both cw and pulsed form, down to single-cycles or less, with peak powers up to 10 MW. New sources have led to new science in many areas, as scientists begin to become aware of the opportunities for research progress in their fields using THz radiation.
Science at a Time Scale Frontier: THz-frequency electromagnetic radiation, with a fundamental period of around 1 ps, is uniquely suited to study and control systems of central importance: electrons in highly-excited atomic Rydberg states orbit at THz frequencies. Small molecules rotate at THz frequencies. Collisions between gas phase molecules at room temperature last about 1 ps. Biologically-important collective modes of proteins vibrate at THz frequencies. Frustrated rotations and collective modes cause polar liquids (such as water) to absorb at THz frequencies. Electrons in semiconductors and their nanostructures resonate at THz frequencies. Superconducting energy gaps are found at THz frequencies. An electron in Intel’s THz Transistor races under the gate in ~1 ps. Gaseous and solid-state plasmas oscillate at THz frequencies. Matter at temperatures above 10 K emits black-body radiation at THz frequencies. This report also describes a tremendous array of other studies that will become possible when access to THz sources and detectors is widely available. The opportunities are limitless.
Electromagnetic Transition Region: THz radiation lies above the frequency range of traditional electronics, but below the range of optical and infrared generators. The fact that the THz frequency range lies in the transition region between photonics and electronics has led to unprecedented creativity in source development. Solid-state electronics, vacuum electronics, microwave techniques, ultrafast visible and NIR lasers, single-mode continuous-wave NIR lasers, electron accelerators ranging in size from a few inches to a mile-long linear accelerator at SLAC, and novel materials have been combined yield a large variety of sources with widely-varying output characteristics. For the purposes of this report, sources are divided into 4 categories according to their (low, high) peak power and their (small, large) instantaneous bandwidth.
THz experiments: Many classes of experiments can be performed using THz electromagnetic radiation. Each of these will be enabled or optimized by using a THz source with a particular set of specifications. For example, some experiments will be enabled by high average and peak power with impulsive half-cycle excitation. Such radiation is available only from a new class of sources based on sub-ps electron bunches produced in large accelerators. Some high-resolution spectroscopy experiments will require cw THz sources with kHz linewidths but only a few hundred microwatts of power. Others will require powerful pulses with ≤1% bandwidth, available from free-electron lasers and, very recently, regeneratively-amplified lasers and nonlinear optical materials. Time-domain THz spectroscopy, with its time coherence and extremely broad spectral bandwidth, will continue to expand its reach and range of applications, from spectroscopy of superconductors to sub-cutaneous imaging of skin cancer.
What is needed
The THz community needs a network: Sources of THz radiation are, at this point, very rare in physics and materials science laboratories and almost non-existent in chemistry, biology and medical laboratories. The barriers to performing experiments using THz radiation are enormous.
One needs not only a THz source, but also an appropriate receiver and an understanding of many experimental details, ranging from the absorption characteristics of the atmosphere and common materials, to where to purchase or construct various simple optics components such as polarizers, lenses, and waveplates, to a solid understanding of electromagnetic wave propagation, since diffraction always plays a significant role at THz frequencies. There is also significant expense, both in terms of time and money, in setting up any THz apparatus in one’s own lab, even if one is the type of investigator who enjoys building things.
Because of the enormous barriers to entry into THz science, the community of users is presently much smaller than the potential based on the scientific opportunities. Symposia on medical applications of THz radiation are already attracting overflow crowds at conferences. The size of the community is increasing with a clear growth potential to support a large THz user’s network including user facilities. The opportunities are great. The most important thing we can do is lower research barriers.
A THz User’s Network would leverage the large existing investment in THz research and infrastructure to considerably grow the size of the THz research community. The Network would inform the scientific community at large of opportunities in THz science, bring together segments of the community of THz researchers who are currently only vaguely aware of one another and lower the barriers to entry into THz research.
Specific ideas for network activities include disseminating information about techniques and opportunities in THz science through the worldwide web, sponsoring sessions about THz technology at scientific conferences, co-location of conferences from different communities within the THz field, providing funding for small-scale user facilities at existing centers of excellence, directing researchers interested in THz science to the most appropriate technology and/or collaborator, encouraging commercialization of critical THz components, outreach to raise public awareness of THz science and technology, and formation of teams to work on problems of common interest, such as producing higher peak fields or pulse-shaping schemes.
Interagency support is crucial: NIH, NSF, and DOE will all benefit, and all must be involved. Eventually, the network will provide the best and most efficient path to defining what new facilities may be needed. New users of THz methodology will also find it easier to learn about the field when there is a network.
Defining common goals: During the workshop, the community articulated several common and unmet technical needs. This list is far from exhaustive, and it will grow with the network:
1. Higher peak fields.
2. Coverage to 10 THz (or higher) with coherent broad-band sources.
3. Full pulse-shaping.
4. Excellent stability in sources with the above characteristics.
5. Easy access to components such as emitters and receivers,
and for time-domain THz spectroscopy.
6. Near-field THz microscopy.
7. Sensitive non-cryogenic detectors.
