A project by
Nicholas A. Kuhta
Unique properties of a NIM-based planar lens allow it to restore minute
details of the the objects with the resolution far exceeding one of conventional
imaging systems (see superlens simulation). However, to use these great
advantages, the superlens should be placed extremely close to the object. In
fact, the distance from the object to the lens should be much smaller than the
wavelength. In a sense, this distance plays a role of the major limiting factor
in superlens resolution. The other factor is, of course, material absorption. In
this project we design the optimal superlens configuration.
Project Description
Two basic planar lens
configurations were studied in the
course of this work. Specifically,
we have compared the performance of
a conventional symmetric superlens
configuration, where the lens is
centered between the object and the image and an optimal configuration
where the lens thickness is equal to the distance from the object to the front
lens surface. The two configurations are shown below:
|
Symmetric superlens
configuration |
Optimal superlens
configuration |
The symmetric configuration, originally proposed by J.Pendry, has several
practical limitations. First, its performance is strongly limited by the
absorption inside lens material. Second, the maximum intensity is observed at
the back interface of the lens, while the image position is behind the lens.
This particular property of a symmetric superlens configuration has been
considered a major drawback of this device. In the typical microscopy
experiment, the observer does not know the exact shape of the object. Therefore,
he or she would need to scan the whole area behind the symmetric superlens
"looking" for the in-focus image, constantly adjusting the microscope for a
rapidly changing average intensity.
The optimal configuration solves
both problems mentioned above.
Indeed, the thickness of the optimal
superlens is half of that in
symmetric configuration. Therefore,
the total absorption inside the
material is reduced and resolution
is increased. On the other hand, the
image is now positioned exactly at
the back interface of the device,
and coincides with the point of
maximum intensity. No more looking
for it! Just look at the lens edge
and see it!
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Optimizing the
superlens design
Compare the symmetric and optimal configurations yourself. You need
Java installed on your machine to run the
applet. If you prefer not to install Java - please scroll down to see some
representative screenshots.
Setup the parameters in the input lines below, and click either "Calculate all"
or "Calculate 1D plots". Don't hurry - it may take up to several minutes for a
computer to simulate the full 2D imaging graphs. When looking at images, compare
the size of the image to the size of the object. Note that the image is
typically thicker than the object -
a consequence of finite resolution
of any lens (including a super-lens). The closer the image size to the object
size - the better the resolution. Note that the resolution of an optimal
superlens is always better than the one of its symmetric counterpart.
You can control:
- Size of the object [from 0.1
l to 2
l]
- The focal distance of the lens
(the lens thickness is twice its
focal distance) [from 0 to 15*object
size]
- Absorption in the NIM part [from
10-6 to 10-2]
(enter the exponent of absorption)
- The blue one dimensional plot
represents a cross section of the
H-Field in the yz plane.
- The red one dimensional plot
represents a cross section of the
H-Field in the xy plane located at
the image.
- The dashed yellow lines on the
density plot represent the boundary
of the planar lenses.
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Some representative
screenshots of
the applet:
Super-imaging regime. Note that the
resolution of the optimal superlens
is almost twice of that of symmetric
one.
Both configurations behave similarly
when the distance between the object
and the lens is larger than the
wavelength (diffraction-limited
regime).
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