Unusual Photon Tunneling Caused by Negative Refraction
Department of Mechanical Engineering
Massachusetts Institute of Technology
In recent years, tremendous efforts have been devoted to a class of novel
metamaterials, left-handed materials (LHMs), which reverse the behavior of many
fundamental electromagnetic properties associated with materials.
In this investigation,
we briefly discuss the application of LHMs in enhancing photon tunneling, which is used
in thermophotovoltaic devices and scanning photon-tunneling microscopy.
As one of the most fundamental phenomena in optics, refraction has been studied for a
In the nature, all known materials exhibit positive refractive indices.
light beam crosses the interface between two positive index media (PIM), it will be bent
positively, i.e., on the opposite side of the normal to the interface.
Snell’s law dictates that
is the angle subtended between the
incident ray and the normal,
is the included angle between the refracted ray and the
are the refractive indices of media 1 and 2, respectively.
Regarded as a common sense by many people, the above knowledge was challenged
after the discovery of negative index media (NIM).
In 1968, Soviet physicist Victor
Veselago first hypothesized the existence of such materials with simultaneous negative
, resulting in an effective negative index of refraction,
Opposite to PIM, the triplet set of vectors
in NIM is left-
handed, and thus they are also called left-handed materials (LHMs).
When a ray of light
passes the PIM-NIM interface, it will be bent negatively according to the Snell’s law.
Due to the negative
values, other fundamental phenomena such as the
Doppler effect, Cerenkov radiation, anomalous refraction, and radiation pressure will also
be reversed [2, 3].
Although little attention was paid to LHMs for almost thirty years, it has become a
frequently mentioned topic recently since the practical realization of LH materials with
split ring resonators (SRRs) and thin-wire structures were demonstrated [3, 4].
experimental realization based on microwave scattering was accomplished in 2001 .
Although divergent views were held on the explanation of the experimental data and its
theoretical foundation was also questioned [6, 7], negative refraction has recently been
reconfirmed in both experiments and theories [8-12].
For applications, research is
actively conducted on a perfect lens  and unusual photon tunneling phenomena .
In this paper, we investigate the possibilities of using LHMs to enhance the photon
tunneling through a vacuum gap.
Our discussion will focus on thermophotovoltaic
devices and scanning photon-tunneling microscopy.
The paper is divided into three
The first section briefly introduces the idea of using LHMs to amplify
evanescent waves in a perfect lens.
The second section demonstrates this idea based on