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The Strange Properties of
Left-handed Materials
C. M. SoukoulisAmes Lab. and Physics Dept. Iowa State University
andResearch Center of Crete, FORTH - Heraklion, Crete
Outline of Talk• Historical review left-handed materials
• Results of the transfer matrix method
• Determination of the effective refractive index
• Negative n and FDTD results in PBGs (ENE & SF)
• New left-handed structures• Experiments on negative refraction and
superlenses (Ekmel Ozbay, Bilkent)
• Applications/Closing Remarks
Peter Markos, E. N. Economou & S. Foteinopoulou
Rabia Moussa, Lei Zhang & Gary Tuttle (ISU) M. Kafesaki & T. Koschny (Crete)
A composite or structured material that exhibits properties not found in naturally occurring materials or compounds.
Left-handed materials have electromagnetic properties that are distinct from any known material, and hence are examples of metamaterials.
What is an Electromagnetic Metamaterial?
Veselago
We are interested in how waves propagate through various media, so we consider solutions to the wave equation.
(+,+)(-,+)
(-,-) (+,-)
space
€
k = ω εμ
€
∇2E = εμ∂2E∂t2 n = ± εμ
Sov. Phys. Usp. 10, 509 (1968)
Left-Handed Waves
• If then is a right set of vectors:
• If then is a left set of vectors:
0,0 >> ( )kHErrr
,,
0,0 << ( )kHErrr
,,
Er
kr
Hr
• Energy flux (Pointing vector):
– Conventional (right-handed) medium
– Left-handed medium
Energy flux in plane waves
Er
kr
Hr
Er
kr
Hr S
r
Frequency dispersion of LH medium
• Energy density in the dispersive medium
• Energy density W must be positive and this requires
• LH medium is always dispersive
• According to the Kramers-Kronig relations – it is always dissipative
( )0>
∂
∂
ω
μω
( ) ( ) 22 HEWω
μω
ω
εω
∂
∂+
∂
∂=
( );0>
∂
∂
ω
εω
“Reversal” of Snell’s Law
1
2
12
PIMRHM
PIMRHM
PIMRHM
NIMLHM
(1) (2) (1) (2)
kr
Sr k
r
Sr
n=-1n=1 n=1
RH RHLHRH RHRH
n=1.3n=1 n=1
Focusing in a Left-Handed Medium
Left-handedLeft-handed Right-handedRight-handed
SourceSource SourceSource
n=-1 n=1,52
n=1
n=1
n=1
n=1
M. Kafesaki
Objections to the left-handed ideas
S1 S2
A BO΄Μ
ΟCausality is violated
Parallel momentum is not conserved
Fermat’s Principle ndl minimum (?)
Superlensing is not possible
Reply to the objections
• Photonic crystals have practically zero absorption
• Momentum conservation is not violated
• Fermat’s principle is OK
• Causality is not violated
• Superlensing possible but limited to a cutoff kc or 1/L
€
ndl extremum∫
guS υrr
=
Sr
kr
ωα
d
nndl+≡1
0>αn
0, kn
cp
pg
rrr
r== υ
αυ
υ
€
rp =
εμc 2
r S +
r k
8π∂ε∂ω
r E 2 +
∂μ∂ω
r H 2
⎡ ⎣ ⎢
⎤ ⎦ ⎥ k
up
rrω
=
gυr kr
guS υrr
=
Sr
ωα
d
nndl+≡1
ωkc
n
r
=
0,
0,,0
<−>+
±=⇒>αα
α nnn
0, kn
cp
pg
rrr
r== υ
αυ
υ
Materials with < 0 and <0 Photonic Crystals
opposite to
opposite to
opposite to kr
gυr opposite to kr
,
Super lenses
€
ω2 = c 2 k||2 + k⊥
2( )⇒ if k|| > ω/c⇒ k⊥
€
e ik⊥r⊥ ~ e− k⊥ r⊥is imaginary
Wave components with decay, i.e. are lost , then max
If n < 0, phase changes sign
€
e ik⊥r⊥ ~ e k⊥ r⊥
ck /|| ω>
if imaginary ⊥k
⊥k
k
€
k||
ARE NOT LOST !!!
thus
Resonant response
-5
0
5
10
0 0.5 1 1.5 2 2.5 3
ω/ω0
qE
p
q
E p
qEp
Where are material resonances?
Most electric resonances are THz or higher.
For many metals, ωp occurs in the UV
Magnetic systems typically have resonances through the GHz (FMR, AFR; e.g., Fe, permalloy, YIG)
Some magnetic systems have resonances up to THz frequencies (e.g., MnF2, FeF2)
Metals such as Ag and Au have regions where <0, relatively low loss
Negative materials
<0 at optical wavelengths leads to important new optical phenomena.
<0 is possible in many resonant magnetic systems.
What about <0 and <0?
Unfortunately, electric and magnetic resonances do not overlap in existing materials.
This restriction doesn’t exist for artificial materials!
Obtaining electric response
-5
-4
-3
-2
-1
0
1
0 1 2 3
ω/ωp
0
0.5
1
1.5
2
ω/ω
p
k
Drude Model
-E-
-
-
-
Gap
€
(ω) = 1−ω p
2
ω2
€
ω =c
εk
€
ωp2 =
2πc 2
d2 ln(d / r)=
1d2Lε 0
Obtaining electric response (Cut wires)
Drude-Lorentz
E 0
0.5
1
1.5
2
ω/ω
p
k-10
-5
0
5
10
0 1 2 3
ω/ωp
- -
-- -
Gap
€
(ω) = 1−ω p
2
ω 2 − ω02
€
ω =c
μk
Obtaining magnetic response
To obtain a magnetic response from conductors, we need to induce solenoidal currents with a time-varying magnetic field
A metal disk is weakly diamagnetic
A metal ring is also weakly diamagnetic
Introducing a gap into the ring creates a resonance to enhance the response
H
+
+
-
-
Obtaining magnetic response
-3
-2
-1
0
1
2
3
0 1 2
ω/ωmp
0
0.5
1
1.5
2
ω/ω
mp
k
Gap
€
ω =c
μk
€
(ω) = 1−Fω p
2
ω 2 − ω02
Metamaterials Resonance Properties
€
ω( ) =1−ω p
2
ω2
€
ω( )=1−ω p
2
ω 2 −ω02
J. B. Pendry
First Left-Handed Test Structure
UCSD, PRL 84, 4184 (2000)
Wires alone
<0
Wires alone
Split rings alone
Transmission Measurements
4.5 7.05.0 5.5 6.0 6.5
Frequency (GHz)
Tra
nsm
itte
d P
ower
(dB
m)
>0<0>0
>0<0>0 <0<0
<0
UCSD, PRL 84, 4184 (2000)
Best LH peak observed in left-handed materials
Bilkent, ISU & FORTHw
t
dr1
r2
Single SRR Parameters: r1 = 2.5 mm r2 = 3.6 mm d = w = 0.2 mm t = 0.9 mm
A 2-D Isotropic Structure
UCSD, APL 78, 489 (2001)
Measurement of Refractive Index
UCSD, Science 292, 77 2001
Measurement of Refractive Index
UCSD, Science 292, 77 2001
Measurement of Refractive Index
UCSD, Science 292, 77 2001
Boeing free space measurements for negative refraction
PRL 90, 107401 (2003) & APL 82, 2535 (2003)
n
Transfer matrix is able to find:
• Transmission (p--->p, p--->s,…) p polarization
• Reflection (p--->p, p--->s,…) s polarization
• Both amplitude and phase• Absorption
Some technical details:
• Discretization: unit cell Nx x Ny x Nz : up to 24 x 24 x 24
• Length of the sample: up to 300 unit cells• Periodic boundaries in the transverse direction• Can treat 2d and 3d systems • Can treat oblique angles• Weak point: Technique requires uniform discretization
Structure of the unit cell
Periodic boundary conditionsare used in transverse directions
Polarization: p wave: E parallel to y s wave: E parallel to x
For the p wave, the resonance frequencyinterval exists, where with Re eff <0, Re eff<0 and Re np <0.For the s wave, the refraction index ns = 1.
Typical permittivity of the metallic components: metal = (-3+5.88 i) x 105
EM wave propagates in the z -direction
Typical size of the unit cell: 3.3 x 3.67 x 3.67 mm
Generic LH related Metamaterials
€
′ ω p
€
′ ω p
€
ωm
€
ωm
€
′ ω m
€
′ ω m
€
ωa/c
€
ωa/c
€
ωa/c
€
€
Resonance and anti-resonance
Typical LHM behavior
f (GHz)
T
30 GHz FORTH structure with 600 x 500 x 500 m3
SubstrateGaAsb=12.3
LHM Design used by UCSD, Bilkent and ISU
LHMSRRClosed LHM
T and R of a Metamaterial
€
ts =exp(−ikd)
cos nkd( )−1
2z +
1
z ⎛ ⎝
⎞ ⎠sin nkd( )
€
z =με
€
n = με
€
ω( )=1−ωmp
2
ω 2 −ω m02 + iΓm0
€
ω( ) =1−ωep
2
ω2 −ω e02 + iΓe 0
UCSD and ISU, PRB, 65, 195103 (2002)
€
rs = − ts exp(+ikd)i(z −1 / z)sin(nkd) / 2
d
z, n
Inversion of S-parameters
d
UCSD and ISU, PRB, 65, 195103 (2002)
€
e ik
€
teik
€
re− ik
€
=nz
€
=nz
€
n =1kd
cos−1 12 ′ t
1− r 2 − ′ t 2( )[ ]
⎛ ⎝
⎞ ⎠ +
2πmkd
€
z = ±1 + r( )
2− ′ t 2
1− r( )2 − ′ t 2
Effective permittivity ω and permeability ω of wires and SRRs
UCSD and ISU, PRB, 65, 195103 (2002)
€
ω( ) =1−ω p
2
ω2
€
ω( )=1−ωm
2
ω 2 − ω02 + iΓω
UCSD and ISU, PRB, 65, 195103 (2002)
Effective permittivity ω and permeability ω of LHM
UCSD and ISU, PRB, 65, 195103 (2002)
Effective refractive index nω of LHM
b=4.4
New designs for left-handed materials
Bilkent and ISU, APL 81, 120 (2002)
Bilkent & FORTH
Photonic Crystals with negative refraction.
Triangular lattice of rods with =12.96 and radius r, r/a=0.35 in air. H (TE) polarization.
Same structure as in Notomi, PRB 62,10696 (2000)
CASE 1
CASE 2
PRL 90, 107402 (2003)
Photonic Crystals with negative refraction.
υg
υg
Equal Frequency Surfaces (EFS)
Schematics for Refraction at the PC interface
EFS plot of frequency a/ = 0.58
Experimental verification of negative refraction
a
Lattice constant a=4.794 mmDielectric constant=9.61R/a=0.329Frequency=13.698 GHzsquare lattice E(TM) polarization
Bilkent & ISU
Band structure, negative refraction and experimental set up
Bilkent & ISU
Negative refraction is achievable in this frequency
range for certain angles of incidence.
Frequency = 13.7 GHz = 21.9 mm
17 layers in the x-direction and 21 layers in the y-direction
Superlensing in photonic crystals
FWHM = 0.21
Image Plane
Distance of the source from the PC interface is 0.7 mm (/30)
Subwavelength Resolution in PC based Superlens
The separation between the two point sources is /3
Subwavelength Resolution in PC based Superlens
The separation between the two point sources is /3 !
Power distribution along the image plane
Controversial issues raised for negative refraction
PIM NIMAmong othersAmong others
1) What are the allowed signs for the phase index np and group index ng ?
2) Signal front should move causally from AB to AO to AB’; i.e. point B reaches B’ in infinite speed.
Does negative refraction violate causalityviolate causality and the speed of light limitspeed of light limit ?
Valanju et. al., PRL 88, 187401 (2002)
Photonic Crystals with negative refraction.
FDTD simulations were used to study the time evolution of an EM wave as it hits the interface vacuum/photonic crystal.Photonic crystal consists of an hexagonal lattice of dielectric rods with =12.96. The radius of rods is r=0.35a. a is the lattice constant.
PhotonicCrystal
vacuum
QuickTime™ and aBMP decompressor
are needed to see this picture.
We use the PC system of case1 to address the controversial issue raised
Time evolution of negative refraction shows:
The wave is trapped initially at the interface.
Gradually reorganizes itself.
Eventually propagates in negative direction
Causality and speed of light limit not violated
S. Foteinopoulou, E. N. Economou and C. M. Soukoulis, PRL 90, 107402 (2003)
Photonic Crystals: negative refraction
The EM wave is trapped temporarily at the interface and after a long time,the wave front moves eventually in the negative direction. Negative refraction was observed for wavelength of the EM wave = 1.64 – 1.75 a (a is the lattice constant of PC)
Conclusions
• Simulated various structures of SRRs & LHMs • Calculated transmission, reflection and absorption• Calculated eff and eff and refraction index (with UCSD)
• Suggested new designs for left-handed materials• Found negative refraction in photonic crystals • A transient time is needed for the wave to move along the - direction• Causality and speed of light is not violated.• Existence of negative refraction does not guarantee the existence of negative n and so LH behavior• Experimental demonstration of negative refraction and superlensing• Image of two points sources can be resolved by a distance of /3!!!
$$$ DOE, DARPA, NSF, NATO, EU
Publications:
P. Markos and C. M. Soukoulis, Phys. Rev. B 65, 033401 (2002) P. Markos and C. M. Soukoulis, Phys. Rev. E 65, 036622 (2002) D. R. Smith, S. Schultz, P. Markos and C. M. Soukoulis, Phys. Rev. B 65, 195104 (2002) M. Bayindir, K. Aydin, E. Ozbay, P. Markos and C. M. Soukoulis, APL 81, 120 (2002) P. Markos, I. Rousochatzakis and C. M. Soukoulis, Phys. Rev. E 66, 045601 (R) (2002) S. Foteinopoulou, E. N. Economou and C. M. Soukoulis, PRL 90, 107402 (2003) S. Foteinopoulou and C. M. Soukoulis, Phys. Rev. B 67, 235107 (2003) P. Markos and C. M. Soukoulis, Opt. Lett. 28, 846 (2003) E. Cubukcu, K. Aydin, E. Ozbay, S. Foteinopoulou and CMS, Nature 423, 604 (2003) P. Markos and C. M. Soukoulis, Optics Express 11, 649 (2003) E. Cubukcu, K. Aydin, E. Ozbay, S. Foteinopoulou and CMS, PRL 91, 207401 (2003) T. Koshny, P. Markos, D. R. Smith and C. M. Soukoulis, PR E 68, 065602(R) (2003)
PBGs as Negative Index Materials (NIM)
Veselago : Materials (if any) with < 0 and < 0
> 0 Propagation k, E, H Left Handed (LHM) S=c(E x H)/4 opposite to k
Snell’s law with < 0 (NIM)
υg opposite to k
Flat lenses
Super lenses
€
n = − εμ
xy
z
t
wt»w
t=0.5 or 1 mmw=0.01 mm
l=9
cm
3 mm
3 mm
0.33 mm
0.33 mm
Periodicity:ax=5 or 6.5 mmay=3.63 mmaz=5 mm
Number of SRRNx=20Ny=25Nz=25
ax
0.33 mm
Polarization: TM
E
B
y
x
ax=6.5 mmt= 0.5 mm
Bilkent & ISU APL 81, 120 (2002)