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I. I. Smolyaninov and V. N. Smolyaninova
microscope was to detect evanescent optical waves in very close proximity to a studied sample using a near-field scanning optical microscope (NSOM) [1]. Although
many fascinating results are being obtained with NSOM, such microscopes are not as
versatile and convenient to use as regular far-field optical microscopes. For example,
an image from a near-field optical microscope is obtained by point-by-point scanning, which is an indirect and a rather slow process, and can be affected by artifacts
of the sample.
Over the past twenty years two major new thrusts have developed in optical
microscopy, which are quickly demolishing the resolution barrier due to the diffraction limit. The first one is making use of nonlinear optics. A comprehensive review
of this major research thrust has been published recently by Hell [2]. Broadly speaking, these techniques rely on photo-switching and/or saturation of fluorescence from
individual molecules. They demonstrate far-field resolution of 20–30 nm, which is
limited by light collection. Unfortunately, this technique also relies on scanning,
which is a slow process. A parallel revolutionary development in usual linear optical
microscopy was inspired by seminal paper by Pendry [3] and the following extraordinary progress in the optics of metamaterials. According to the Pendry’s idea of
a flat “perfect lens” made from an artificial negative refractive index metamaterial,
a high resolution optical image could be obtained by amplified evanescent waves
(surface plasmon polaritons) which live at the interface between the positive and
negative index media. However, according to the original proposal, such an image
would be observable only in the near-field of a perfect lens, and would require an
auxiliary near-field microscope. Indeed, imaging of this kind has been reported in
2005 in two independent experiments performed by Zhang’s group [4] and Blaikie’s
group [5]. Nevertheless, this technique is limited by the fact that magnification of
the planar superlens is equal to 1.
An important early step to overcome this limitation was made in surface plasmonassisted microscopy experiments [6], in which two-dimensional (2D) image magnification has been achieved in the “geometric optics” mode, as shown in Fig. 13.1b.
The increased spatial resolution of microscopy experiments performed with surface
plasmon polaritons [7] is based on the “hyperbolic” dispersion law of such waves,
which may be written in the form
k
2
xy − |k z |
2
=
ε d ω
2
c 2
(13.1)
where ε d is the dielectric constant of the medium bounding metal surface, k xy = k p
is the wave vector component in the plane of propagation, and k z is the wave vector
component perpendicular to the plane. This form of the dispersion relation originates
from the exponential decay of the surface wave field away from the propagation plane.
Negative refractive index behavior of surface plasmons was also shown to play a very
important role in these early experiments [8].
On the theoretical side, various new geometries exhibiting image magnification
beyond the usual diffraction limit were proposed [9–11], which make use of newly
developed optical metamaterials. For example, in the “optical hyperlens” design
I. I. Smolyaninov and V. N. Smolyaninova
microscope was to detect evanescent optical waves in very close proximity to a studied sample using a near-field scanning optical microscope (NSOM) [1]. Although
many fascinating results are being obtained with NSOM, such microscopes are not as
versatile and convenient to use as regular far-field optical microscopes. For example,
an image from a near-field optical microscope is obtained by point-by-point scanning, which is an indirect and a rather slow process, and can be affected by artifacts
of the sample.
Over the past twenty years two major new thrusts have developed in optical
microscopy, which are quickly demolishing the resolution barrier due to the diffraction limit. The first one is making use of nonlinear optics. A comprehensive review
of this major research thrust has been published recently by Hell [2]. Broadly speaking, these techniques rely on photo-switching and/or saturation of fluorescence from
individual molecules. They demonstrate far-field resolution of 20–30 nm, which is
limited by light collection. Unfortunately, this technique also relies on scanning,
which is a slow process. A parallel revolutionary development in usual linear optical
microscopy was inspired by seminal paper by Pendry [3] and the following extraordinary progress in the optics of metamaterials. According to the Pendry’s idea of
a flat “perfect lens” made from an artificial negative refractive index metamaterial,
a high resolution optical image could be obtained by amplified evanescent waves
(surface plasmon polaritons) which live at the interface between the positive and
negative index media. However, according to the original proposal, such an image
would be observable only in the near-field of a perfect lens, and would require an
auxiliary near-field microscope. Indeed, imaging of this kind has been reported in
2005 in two independent experiments performed by Zhang’s group [4] and Blaikie’s
group [5]. Nevertheless, this technique is limited by the fact that magnification of
the planar superlens is equal to 1.
An important early step to overcome this limitation was made in surface plasmonassisted microscopy experiments [6], in which two-dimensional (2D) image magnification has been achieved in the “geometric optics” mode, as shown in Fig. 13.1b.
The increased spatial resolution of microscopy experiments performed with surface
plasmon polaritons [7] is based on the “hyperbolic” dispersion law of such waves,
which may be written in the form
k
2
xy − |k z |
2
=
ε d ω
2
c 2
(13.1)
where ε d is the dielectric constant of the medium bounding metal surface, k xy = k p
is the wave vector component in the plane of propagation, and k z is the wave vector
component perpendicular to the plane. This form of the dispersion relation originates
from the exponential decay of the surface wave field away from the propagation plane.
Negative refractive index behavior of surface plasmons was also shown to play a very
important role in these early experiments [8].
On the theoretical side, various new geometries exhibiting image magnification
beyond the usual diffraction limit were proposed [9–11], which make use of newly
developed optical metamaterials. For example, in the “optical hyperlens” design