Transcript Negative Index of Refraction - University of California, Davis

Negative Index of
Refraction
By: Jason Kaszpurenko
Journal Club
1/16/09
Overview
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Both articles that I read were from a Materials Research
Society October 2008 Bulletin
General Overview about negative index materials:
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Making Negative Index of Refraction materials
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What is ti
What properties does it have
What possible applications
Two types of Negative Index Materials
Attempts to get into the optical range
Questions (Yours and mine)
Overview
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Negative index of refraction
was first theorized by Victor
Veselago in 1968
The idea that a material could
have both negative permittivity
and permeability
If it had both of these it would
not violate the laws of physics
First confirmed by J. Pendry in
2000
Overview
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Index of refraction is normally defined by
 n=c/v or n=(εμ)^0.5
 c is the speed of light
in vacuum, v is the speed of
light in a medium, ε is permittivity and μ is
permeability
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ε can be found negative naturally in several
metals such as gold and silver but μ needs to be
engineered artificially to be negative
The shortest wavelength observed with this
property is 710 nm
Overview
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In a normal material the k, E and H
of the material right handed set
(good old right hand rule)
In negative index materials (NIM) the
k, E and H form a left handed set
(your students were doing it for
negative index of materials)
This causes the wave’s phase front
to move in the opposite direction of
the wave itself
The energy of the wave is associated
with the group velocity
To the right we have an example of
this. The Gaussian wave packet
moves to the right while the wave
front, (red point) moves to the left
W. Park, J. Kim, MRS bulletin Oct 2008
Optical Properties of negative index
materials
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Negative index materials can be used to
make:
 Electromagnetic
 Super
cloaking devices
lenses
 filters
 Sub
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wavelength waveguides and antennas
I’m going to talk about the super lenses
Super lenses
In most optics the limiting factor is the
wavelength of light
 The evanescent waves, waves which
exponentially decay in mater, actually
contain information that is smaller than the
wavelength, but this is normally lost
 In negative index materials the evanescent
waves are actually enhanced
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Evanescent waves
W. Park, J. Kim, MRS bulletin Oct 2008
Image a: The red lines represent the
evanescent waves fon n<0 with the light
getting focused. While the blue dotted
are for n>0 and the light getting
scattered. Image b is the amplitude of
the evanescent light in negative and
positive materials. Image c shows a
simulation of this phenomenon. The
smaller image than source size means
enhanced evanescent waves.
Elaboration of conditions needed
for negative index materials
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Originally Veselago argued that you need the real and
complex parts of permeability and permittivity to be
negative
This is an over constrained condition the real one is:
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ε’μ”+ ε”μ’<0 (’ is real and ” is complex part)
If ε’<0 or μ’<0 we have a single-negative NIM (SN-NIM)
If ε’<0 and μ’<0 we have a double-negative NIM (DNNIM), DN-NIM have the potential to have less losses and
are considered better because of this
Making μ < 0
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Three common types of magnetic resonators are
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Bihelix (figure a) this resonator uses two separate strips of the same metal
Split-ring resonators (SRR) (figure b) uses to different rings and is a very
common choice but the magnetic response becomes saturated in the visual
regime.
 Pair of Nanorods is the last configuration, this was used by the authors to get into
the optical regime
Chettiar, et all, MRS bulletin Oct 2008
Synthesis
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An attempt was made to
synthesize nanorods with
different deposition rates
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Al2O3 was deposited in
between the layers Ag
nanorods
Sample A was deposited at
2 A/s while sample B was
deposited at 0.5 A/s
Using AFM cross sections
we can see that the faster
deposition rate created
(right) a rougher surface
than the slower
deposition (lower right)
Chettiar, et all, MRS bulletin Oct 2008
Permittivity and Permeability
Sample A has a high
deposition rate and
Sample B has a low
deposition rate
Chettiar, et all, MRS bulletin Oct 2008
Results for different spacing
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When varying the spacing of
the magnets are verried
different frequencies of light
are allowed to pass, but
electrons view it is a metal
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Image a: Transmission mode
with TM polarization
Image b: Transmission mode
with TE polarization
Image c: Reflection mode with
TM polarization
Image d: Reflection mode with
TE polarization
Conclusion
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Although theorized over 40 years ago NIM have only
been made within the last decade
NIM act in many unconventional ways, wave phase front
moves in opposite direction of group velocity,
evanescent waves increase….
These properties lend themselves to making unique
devices like super lenses that can overcome traditional
optical limits
The difficulty in making them comes from the negative
permeability, which has to be artificially manufactured
The optical regime is just being realized
Questions
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How does varying the oxide material in-between
the nanorods effect the index of refraction
With evanescent waves increasing in amplitude,
how is energy being conserved?
What attempts have there been on working on
different materials with a negative permittivity