Terahertz radiation



light).

 

Introduction

Like infrared radiation or metal or water.

The Earth's atmosphere is a strong absorber of terahertz radiation, so the range of terahertz radiation is quite short, limiting its usefulness. In addition, producing and detecting coherent terahertz radiation was technically challenging until the 1990s.

Sources

While terahertz radiation is emitted as part of the terahertz time-domain spectroscopy generated a great deal of interest, and sparked a rapid growth in the field of terahertz science and technology. This excitement, along with the associated coining of the term "T-rays," even showed up in a contemporary novel by Tom Clancy.

There have also been solid-state sources of millimeter and submillimeter waves for many years. AB Millimeter in Paris, for instance, produces a system that covers the entire range from 8 GHz to 1000 GHz with solid state sources and detectors. Nowadays, most time-domain work is done via ultrafast lasers.

In the fall of 2007, scientists at the U.S. Department of Energy's Argonne National Laboratory, along with collaborators in Turkey and Japan, announced the creation of a compact device that can lead to a portable, battery-operated sources of T-rays, or terahertz radiation. The group was led by Ulrich Welp of Argonne's Materials Science Division. [1]

The new T-ray sources created at Argonne use high-temperature superconducting crystals grown at the University of Tsukuba in Japan. These crystals comprise stacks of so-called Josephson junctions that exhibit a unique electrical property: when an external voltage is applied, an alternating current will flow back and forth across the junctions at a frequency proportional to the strength of the voltage; this phenomenon is known as the Josephson effect.

These alternating currents then produce electromagnetic fields whose frequency is tuned by the applied voltage. Even a small voltage – around two millivolts per junction – can induce frequencies in the terahertz range, according to Welp.

Theoretical and technological uses under development

  • Medical imaging:
    • Terahertz radiation is non-ionizing, and thus is not expected to damage tissues and density of a tissue. Such methods could allow effective detection of epithelial cancer with a safer and less invasive or painful system using imaging.
    • Some frequencies of terahertz radiation can be used for 3D imaging of teeth and may be more accurate and safer than conventional X-ray imaging in dentistry.
  • Security:
    • Terahertz radiation can penetrate fabrics and plastics, so it can be used in surveillance, such as security screening, to uncover concealed weapons on a person, remotely. This is of particular interest because many materials of interest, such as plastic explosives, have unique spectral fingerprints in the terahertz range. This offers the possibility to combine spectral identification with imaging. Some controversy surrounds the privacy issues in using terahertz scanners for routine security checks due to the ability to produce detailed images of a subject's body through clothing, though this method is less invasive than a strip search.
  • Scientific use and imaging:
    • biochemistry.
    • Recently developed methods of laser source or experiment. However, THz-TDS produces radiation that is both coherent and broadband, so such images can contain far more information than a conventional image formed with a single-frequency source.
    • A primary use of submillimeter waves in physics is the study of condensed matter in high magnetic fields, since at high fields (over about 15 Larmor frequencies are in the submillimeter band. This work is performed at many high-magnetic field laboratories around the world.
    • A fast growing use is in millimeter/submillimeter wave astronomy.
  • Communication:
    • Potential uses exist in high-altitude telecommunications, above altitudes where water vapor causes signal absorption: aircraft to satellite, or satellite to satellite.
  • Manufacturing:
    • Many possible uses of terahertz sensing and imaging are proposed in manufacturing, quality control, and process monitoring. These generally exploit the traits of packaged goods.

Terahertz versus submillimeter waves

The terahertz band, covering the wavelength range between 0.1 and 1 mm, is identical to the submillimeter wavelength band. However, typically, the term "terahertz" is used more often in marketing in relation to generation and detection with pulsed lasers, as in terahertz time domain spectroscopy, while the term "submillimeter" is used for generation and detection with microwave technology, such as harmonic multiplication.[citation needed]

References and notes

  • "Revealing the Invisible". Ian S. Osborne, Science 16 August 2002; 297: 1097.
  • Article in Nature 14 November 2002 (local copy from the Jefferson Lab)]
  • News and Views in Nature 14 November 2002 (local copy from the Jefferson Lab)
  • Instrumentation for millimeter-wave magnetoelectrodynamic investigations... Review of Scientific Instruments, 2000
  1. ^ Science News: New T-ray Source Could Improve Airport Security, Cancer Detection, ScienceDaily (Nov. 27, 2007).

Books on millimeter and submillimeter waves and RF optics

  • Quasioptical systems: Gaussian beam quasioptical propagation and applications, Paul F. Goldsmith, IEEE Press
  • Millimeter wave spectroscopy of solids, edited by G. Grüner, Springer
  • Detection of light: from the ultraviolet to the submillimeter, George Rieke, Cambridge
  • Modern millimeter-wave technologies, Tasuku Teshirogi and Tsukasa Yoneyama, eds, IOS press
  • Optoelectronic techniques for microwave and millimeter-wave engineering William Robertson, Artech

See also

v • d • e
Longwave
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Terahertz_radiation". A list of authors is available in Wikipedia.