Plasmonic metamaterials: unusual optics and applicationsIgor Smolyaninov

BAE Systems, Advanced Technologies1250 24th Street NW, Suite 800

Washington DC 20037igor.smolyaninov@baesystems.com

C.C.Davis Y.J.Hung E. Hwang(University of Maryland)

J.Elliott G.Wurtz A.V.Zayats(Queen’s University of Belfast, UK)

A. A. Maradudin(University of California, Irvine)

L. Le Guyader A. KirilyukTh. Rasing(Radboud University Nijmegen, The Netherlands)

Acknowledgement: NSF , DoD

I gratefully acknowledge collaboration with

Acknowledgement

- Optics beyond diffraction: theoretical approach - Magnifying superlens action is based on surface

plasmon optics: what are surface plasmons? - Surface plasmon optics – optics in 2D- Bioimaging and biosensing applications of plasmon optics

- Plasmons bit 3D diffraction limit- Negative refraction in plasmon optics- Optical metamaterials - media without diffraction

limit- Magnifying superlens / Optical hyperlens- What next? Plasmonics/Spintronics?

OUTLINE

OPTICS BEYOND DIFFRACTION -RECENT HEADLINES

Abbé diffraction limit of far-field optics

immersionmicroscopy

( )ωεω2

222222

ckkkkk zyxobject =++=≤

immersion material (fluid)

What about diffraction limit in a metamaterial?

Metamaterials

Science magazine called metamaterialsone of the top ten breakthroughs in 2003

negative refraction

There is no diffraction limit in a “hyperbolic metamaterial”(Narimanov, Engheta, Pendry, Smith)

Narimanov’s hyperlens

2

222

|| ckk

r

r ωεε

θ

θ

=−

εr and εθ may have opposite signsin a metamaterial

2

222

ckk

r

r ωεε

θ

θ

=+“normal” anisotropic material:

kresolution:

Immersion microscope based on a hyperbolic metamaterial: resolution is defined by losses

if k2z is negative - surface

wave - kxy > 2π n / λ0

Far-field microscopy using surfaceplasmons beats regular immersion microscopy:

Smolyaninov, et al., Phys.Rev.Letters 94, 057401 (2005) Smolyaninov, et al., Optics Letters 30, 382-384 (2005)

( ) 22

2222

zyxxy kc

kkk −=+= ωεω

immersion hyperbolic metamaterial

CONCEPT:

FIRST REALIZATION:

metal

dielectric 2

dielectric 1z

Magnifying superlens action is based on surface plasmon opticsWHAT ARE SURFACE PLASMONS?

• A plasmon is a surface wave of charge density

• A classical solutions to Maxwell’s equations at the interface between a dielectric and a metal

• A metal is a dense low temperature plasma – electrons are very mobile – Fermi liquid

EXCITATION OF PLASMONS

light line light line indielectric

Momentum mismatch

phot

pl

kk

=αsin

gold filmperforated by holes

k

c*k

/a/a−π/a π/a

ω ω = c*k

Kpl=Kphot+2πn/a

Surface plasmon dispersion ω(k)

A. Drezet, A. Hohenau, and J. R. KrennPhys. Rev. Lett. 98, 209703 (2007)

HOW TO VISUALIZE PLASMON OPTICS?

Surface topography of a thin silver film

Propagating plasmon

Near-field optical image of the local field distribution

Localized plasmon

alternatives: fluorescence imaging,scattering

Smolyaninov et al. Phys.Rev.Lett. 77, 3877 (1996)

near-field imaging

Optics with plasmons: demonstration of 2D focusing corresponds to

illumination direction

10 μm

4x4 plasmonic lens array:

Microscopy in Flatland:Geometrical optics in two dimensions

main problem: propagation loss Flatland scientists

Plasmon-assisted imaging of a triplet nanoholetest pattern – performed in liquid ambient!

opticalmicroscope

plasmonmicroscope

SEM

droplet

array of tripletnanoholes

plasmonimage

Two-Dimensional Light

Resolution estimate via higher Fourier components: at least 98 nm

SEMimage

plasmonmicroscope

FFT FFT

reflectedwave

refractedwave

(positive index medium)

(negative index medium)

incidentwave

Momentum conservation requires the projections of momenta to be the same in the incident and refracted waves. If a negative group velocity wave would refract in the “usual” positive direction, accumulation of energy near the interface would occur.

momentumenergy flow

right wrong!

2D negative refractive index materials

momentumenergy flow

momentum

momentum

energy flow

energy flow

S

S E3

E3

Dz = ε(ω) Ez – must becontinuous at the metal-dielectric interface Ez changes sign

6.0µm 2.7µm

430nmng= - 1.73

d1

d2

d1/d2=1.78 average n ~ 0 0.0

0 .5

1 .0

1 .5

2 .0

2 .5

3 .0

0 .0 0 .5 1 .0 1 .5 2 .0 2 .5 3.0 3 .5 4.0 4.5 5 .0 5.5

gold / vacuum

kc(eV)

ω (e

V) gold / PM M A

d

d

ck

εωεεωεω+

=)()(

2

22

Plasmonic metamaterial devices: example

d

dd

εωεεωεε+

=)()(

2

changes sign when ε(ω) ~ εd

Experimental parameters

gold

PMMA

SPP guided modes

n = 0 n = 1 n = 2

metal

dielectric

mutually orthogonal solutions

glass substrate

air

90 nm

50 nm

PMMA

430nm

50nm film

cutoff at h ~ λ/4n

d

d ~ λ in the radial direction

plasmonsources

0.5 μm

d1d2

2.0 μm

X[a.u.]0.00 0.075

Z[a.u

.]-0

.429

0.73

8

Re(n)=-1Im(n)=0.05

distance (μm)

inte

nsity

(arb

.u.)

10.40.0

Demonstration of negative refraction

AFM optical image

Periodicity of PMMA dots produces phase matching condition for efficientexcitation of plasmon “rays”

refractedray

incidentray

interface

cross section along the refracted ray

Similar demonstration of 2D negative refraction

Lezec et al, Science 316, 430 (2007)

Negative refractive index “superlens”

Negative index imaging

experimental geometry:

numerical simulations

white light illumination 532 nm illumination

image magnification=n2/n1 ~ 1.7

gold/air gold/PMMA

regular microscope objective

glass substrate

gold film

plasmon rays

negativerefractive index material

“super”images

samplephase-matching structure

plasmon illumination

laser illumination

magnifyingsuperlens

Magnifying superlens integrated into a far-fieldoptical microscope ( Smolyaninov, et al. Science 315, 1699 (2007)

Test samplesoptical microscope

AFM

PMMA dots (marked by arrows)are used as resolution test patterns

no sampleno image

reverseorientation: no phase matching to plasmonsno image

imageformed

Imaging experiment: 130 nm row spacing, two rows

control #1

control #2

Control #3: Similar PMMA test pattern on ITO: no plasmons, no imaging

Resolution test

optical microscope

cross section of the optical image:

AFM

The FWHM of the beamcorresponds to 70 nm

200 nm

Superposition of the AFM and optical images

plasmon rays

edge scattering

PMMA dots

Narimanov et al.

130 nm dot spacing

X[a.u.]0.00 0.035

Z[a.

u.]

0.07

30.

536

X [ a .u .]0 .0 0 0 .0 9 3

Z[a.

u.]

-0.0

908.

95e

-3

at present the resolution ofoptical images is mostlydefined by fabrication limits:

estimated optical resolutionis ~ 46 nm

130 nm

61 nm

76.5 nm

How reproducible? What is the resolution limit?

AFM

2 rows, 130 nm dot spacing 3 rows, 175 nm dot spacing

Hyperlens from UC Berkeley

Liu et al, Science 315 1686 (2007)

Another application: efficient 2D beam expander/concentrator

layer design helps to fight losses

10 μm

diffraction angle

Transformational optics

Kildishev and Shalaev, Opt.Lett. 33, 43 (2008) “negative index” realization

there is the 4-fold symmetry in the field distribution around the corners (overexposed photo)

Another example : checkerboard structures

S. Guenneau, B. Gralak, and J.B. Pendry, “Perfect corner reflector”Optics Letters 30, 1204 (2005)

Electromagnetic “cloaking” (Pendry, Smith, Shalaev, Engheta)

Can we make an “invisibility cloak”for surface plasmons?

our simulations

ε near zero has been realized – what about plasmonic cloak?

Engheta, et al. PRB 75, 155410 (2007)

ε = 1

ε = 0

4.2µm

4.2µm

10 μm

r1

r2

0 5 10 15 20

0.0

0.5

1.0

1.5

<n>/

n b

r (micrometers)

r1 r2

0 1 2 3 4 5 6

0.5

1.0

1.5

2.0

2.5

3.0

3.5

ω

(eV

)

Ksp (eV)

gold/PMMA

gold/vacuum

430nm

d1

d2

“Plasmonic cloaking” – if it makes sense

thin metal film

2

1

2

12

2 ⎟⎠⎞

⎜⎝⎛ −

⎟⎟⎠

⎞⎜⎜⎝

⎛−

=r

rrrr

rrε

d

dd

εωεεωεε

+=

)()(

2

can be used as an alternative description

Theoretical modeling: cloak made of negative rings

S. John et al. PRE (1998)

refractive indices in the 0<n<1 range may be also emulated by photonic crystal effects:

n=kc/ω in this region n~0

Typical metamaterials have limited bandwidth.Both designs suffer from strong dispersion.

A 2D design based on mirrors is the best:

ω=kc

Theoretical modeling: “photonic crystal” cloak

It looks like the “cloaking” behavior of the graded circular ring structure is model independent

4.2µm10 μm

r1

r2

r1

Experimental results

10 μm

r1r2

r1

Inverse Faraday effect in garnet filmsKimel et al, Nature 435 655 (2005)

The effect of a 200 fs laser pulse on the magnetic system is equivalent to the application of a magnetic field pulse of about 5 T

Inverse Faraday effect:

Faraday effect:

10 μm

r1r2

r1

Inverse Faraday effect in garnet films10 μm

r1

precession frequency as a function of external magnetic field

10 μm

r1

r2

r1

Plasmonics / Spintronics – inverse Faraday effect

4.2µmplasmon induced spin precession

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Question 1

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Question 2

10 μm

r1r2

r1

Inverse Faraday effect in garnet films10 μm

r1

precession frequency as a function of external magnetic field

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Question 3

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Question 4