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Superluminal terahertz pulses.

K Wynne1, D A Jaroszynski

  • 1Femtosecond Research Centre, Department of Physics and Applied Physics, University of Strathclyde, Glasgow G4 0NG, UK.

Optics Letters
|December 12, 2007
PubMed
Summary
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Femtosecond terahertz-pulse (T-ray) imaging reveals that T-rays travel faster than light in vacuum when interacting with sub-wavelength metal structures. This superluminal propagation occurs near metal knife edges and wires, not just in apertures.

Area of Science:

  • Physics
  • Optics
  • Materials Science

Background:

  • Terahertz (T-ray) imaging is a non-ionizing technique used for material characterization.
  • Waveguide effects can lead to superluminal propagation (faster than light) in metallic structures near cutoff frequencies.

Purpose of the Study:

  • To investigate the propagation characteristics of femtosecond terahertz pulses interacting with sub-wavelength metal structures.
  • To analyze the phenomenon of superluminal propagation in T-ray imaging beyond conventional waveguide scenarios.

Main Methods:

  • Femtosecond terahertz-pulse (T-ray) imaging experiments were conducted.
  • Metal structures including apertures, knife edges, and thin wires with dimensions near the T-ray wavelength were used.
  • Time-of-flight measurements were analyzed to determine propagation velocities.

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Main Results:

  • Terahertz pulses propagated faster than the speed of light in vacuum when interacting with metal structures of the order of the wavelength.
  • Superluminal velocities were observed not only in apertures (consistent with waveguide effects) but also near knife edges and thin metal wires.
  • The effect was noted even when not close to the cutoff frequency for apertures.

Conclusions:

  • Superluminal propagation of terahertz pulses is a more general phenomenon in sub-wavelength metallic structures than previously understood.
  • The interaction of T-rays with simple metallic geometries like knife edges and wires can induce apparent faster-than-light propagation.
  • Further research is needed to fully elucidate the mechanisms behind this observed superluminal effect in various metallic configurations.