We experimentally investigate the terahertz energy confinement in finite-width parallel-plate waveguides. Although
there is some apparent energy confinement parallel to the plates due to the narrowing of the width, this does not result in
actual energy conservation, when the plate separation is as large as 1 cm. However, these findings indicate that by
reducing the plate separation, it may be possible to achieve real energy confinement along with energy conservation in
The detection of trace quantities of aromatic compounds is important to defense and security
applications, including the detection of CB agents, explosives, and other substances. These pose
threats to forces and the environment. This paper explores an approach to the detection and
identification of quantities as little as single molecules of explosives. It can in principle provide
Apertureless near-field scanning optical microscopy (ANSOM) is one of several promising
methods for obtaining spatial resolution below the diffraction limit at various wavelengths,
including in the terahertz regime. By scattering incident light off the junction between a probe
with a sub-wavelength tip and the surface of a sample, spatial resolution on the order of the tip
size can be obtained. For terahertz time-domain spectroscopy where the wavelength-limited
resolution is ~1 millimeter, this is a significant advantage.
In the case of a sufficiently small probe tip and a thin metallic substrate, plasmonic interaction
between the tip and sample provides an enhancement of the near-field in the junction. This
effect is dramatically enhanced for nanometer-scale metal layers, since surface plasmon states
from both sides of the film can contribute to the overall field enhancement.
We present preliminary results of THz plasmonic field enhancements, using a thin (500 nm) gold
film evaporated on glass. We observe an enhancement in the scattered THz wave, which we
attribute to the large density of plasmonic states extending throughout the THz range. This result
indicates a route to single-molecule spectroscopy at terahertz frequencies.