Nanoplasmonics and Metamaterials with

Low Loss and GainGuohua Zhu

Center for Materials Research, Norfolk State University, Norfolk, VA

Collaborators:M. A. Noginov, V. I. Gavrilenko, N. Noginova, M. Bahoura, M. Mayy,

A. M. Belgrave, H. Li, J. Adegoke and B. A. RitzoNorfolk State University

V. M. Shalaev, E. E. Narimanov and V. P. DrachevPurdue University

U. Wiesner, S. Stout, E. Herz and T. SuteewongCornell University

V.A. PodolskiyUniversity of Massachusetts at Lowell

A. Urbas and Jarrett VellaAFRL

$$$:NSF PREM grant DMR-0611430, NSF NCN grant EEC-0228390, AFOSR grant FA9550-09-1-0456, and the UTC/AFRL grant #10-S567-0015-02-C4.

Outline

� Introduction

� Enhancement of localized surface plasmon (SP) by gain� SPASER (Nanolaser)

� Enhancement of propagating surface plasmon polariton(SPP) by gain

� Stimulated emission of SPPs

� Enhancement of SPP without Gain� Metal-free optical materials with negative electric permittivity

� Transparent conductive oxides

� High concentrated laser dyes

� Summary

Introductions

EinducedEinduced

SPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

EzSPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

EzSPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

Ez

Localized surface

plasmons (SP)

Dielectric

Metal• Electrons movement at metallic surface

• Oscillations of the

movement upon an EM field interactions

Surface plasmons

polaritons (SPP)

Introductions

Areas and applications of nanoplasmonics:

• Surface Enhanced Raman Scattering

• Near- field microscopy and spectroscopy

• Negative Index Materials - Optical cloaking

• Medical applications, and many others …

Most of existing and potential applications of nanoplasmonics are suffered from the LOSS caused by metal absorption

Enhancement of localized SPs by gains

Enhancement of Localized surfac plasmon (LSP) in the presence of optical gain.

Theoretical predictions:

Localized SP in metallic sphere: Field enhancement in

metallic sphere (R<<λ) with complex dielectric constant ε1 surrounded by dielectric medium with complex dielectric constant ε2:

))(2)(

)()((

21

12

0 ωωωωεεεεωωωωεεεε

ωωωωεεεεωωωωεεεε

++++

−−−−∝∝∝∝

E

Einduced

Lawandy, APL, 2004.

Re=0; Im=0

EinducedEinduced

)]("2)("[)]('2)('[)(2)( 212121 ωωωωεεεεωωωωεεεεωωωωεεεεωωωωεεεεωωωωεεεεωωωωεεεε ++++++++++++====++++ i

LSP enhancement in the presence of optical gain

532 nm laser

pumpR6G&Ag

filterpinhole

mirrormirror

R6G laser

fiber

The mixture of Ag

aggregate and rhodamine

6G dye was pumped at 532

nm and probed at 560 nm.

The scattering of the 560

nm light was studied as a

function pumping.

The enhanced scattering was

used as the evidence of the

plasmon enhancement.

LSP enhancement in the presence of optical gain

0

1

2

3

4

5

6

7

0.001 0.01 0.1 1 10

Pumping (mJ)

Scattering (re

l. u

nits)

Six-fold enhancement of scattering was observed at the increase of

the pumping.

Scattering enhancement ⇒⇒⇒⇒plasmon enhancement

[Noginov, Zhu et.al., ArXiv, 2005; Appl. Phys B, 2006; Opt. Lett. 2006]

Demonstration of Spaser (nanolaser)

Surface Plasmon Amplification by Stimulated Emission of Radiation

Gold Gold w/ Si shell Gold/Si/dye

14 nm 44 nm

58 nm

69 nm

TEM and SEM images of Au/silica particles before the

fluorescent dye was added to the surface

Nanoparticle synthesis –by Cornell

Absorption, Emission and Excitation

SP absorption overlaps with emission and

excitation (absorption) of the Oregon Green 488

dye.

0

0.2

0.4

0.6

0.8

1

1.2

300 400 500 600 700

Wavelength (nm)

Emission, Absorption (rel. units)

12 3

Absorption (1), excitation (2), spontaneous emission (3).

0

100

200

300

400

500

600

700

490 510 530 550 570 590 610 630 650

Wavelength (nm)

225mW

90mW

45mW

20mW

12.5mW0

5

10

15

20

25

490 510 530 550 570 590 610 630 650

Wavelength (nm)

225mW

90mW

45mW

20mW

12.5mW

0

100

200

300

400

500

600

700

0 100 200 300

(Pumping (mW

(Em

issio

n (re

l. u

nits

Pumping: λλλλ=488 nm, tpulse ≈≈≈≈ 5 ns

At dilution, the signal decreased, but its shape and the ratio between the spontaneous and the stimulated

emission did not ⇒⇒⇒⇒Emission occurs in single nanoparticles!

0

0.2

0.4

0.6

0.8

1

490 510 530 550 570 590 610 630 650

Wavelength (nm)

Em

issio

n (

rel. u

nits) more than 100

times diluted

Demonstration of Spaser (nanolaser)

Dye absorption is low, emission and SP resonance are strong

0

0.2

0.4

0.6

0.8

1

1.2

300 400 500 600 700

Wavelength (nm)

12

3

4

Position of the Spaser line

Absorption (1),

Exciatation (2),

Spontaneous emission (3).

Spaser line (4)

[Noginov, Zhu, et. al., Nature 2009]

Surface Plasmon Polaritons (SPPs)

Surface Plasmon Polariton (SPP) is an

electromagnetic wave propagating at

the interface between metal and

dielectric.

At critical angle θθθθ0, when kphotsinθθθθ =

kSPP , light wave excites SPP ⇒⇒⇒⇒ there is a “dip” in the reflection curve.

ω

c⋅ n ⋅ sin θ 0 =

ω

c⋅

ε1 ⋅ε 2

ε1 + ε 2

kphot kSPP

0

0.2

0.4

0.6

0.8

1

1.2

61 63 65 67 69

Angle (dergee)

Refle

ction

red diamonds - experiment

blue line - theory

metal (Ag)glass prism

dielectric

SPPεεεε2

εεεε1

εεεε0=n2

θ0

SPP

0

0.2

0.4

0.6

0.8

1

60 62 64 66 68 70 72

Angle (θ)

PMMA&R6G: εεεε2’ = 1.52, εεεε2”= -0.006gain=422 cm-1

Glass: εεεε0’=1.7842

Silver: εεεε1’ = -15, εεεε1”=0.85

PMMA&R6G: εεεε2’ = 1.52

Thickness of the

silver film ≈≈≈≈39 nm

0

0.0005

0.001

0.0015

0.002

0.0025

0.0E+00 2.0E-07 4.0E-07 6.0E-07 8.0E-07 1.0E-06

Time (s)

Re

fle

ctivity s

ign

al (r

el. u

nits) reflectivity kinetics under

pumping(luminescence is subtracted)

Thin film

d=39nm

Relative enhancement of the reflectivity signal as high as 280% !

SPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

Ez

pumping

Enhancement of SPPs by gains

[Noginov, Zhu, et. al., Optics Express 2008]

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.00E+00 2.00E-07 4.00E-07 6.00E-07 8.00E-07 1.00E-06

Time (s)

Re

fle

ctivity s

ign

al (r

el. u

nits)

Thickness of the silver film is ~ 90 nm

0.000001

0.0001

0.01

1

100

10000

1000000

-0.014 -0.010 -0.006 -0.002

ε " 2

R

1 23 4

5

Trace #1 - 50nm; trace #2 - 60nm;

trace #3 - 70nm; trace #4 - 80nm;

trace #5 - 100nm.

Experimental result is just as the model predicted !

SPPs with optical gain

[Noginov, Zhu, et. al., Optics Express 2008]

SPP spectra recorded at

different

decoupling angles

Emission of SPPs

SPPs can be excited via emission of R6G

molecules in the R6G-PMMA film

SPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

Ez

pumping

Stimulated emission of SPPs

0

0.2

0.4

0.6

0.8

1

1.2

550 570 590 610 630 650

Wavelength, nm

Em

issio

n

below threshold

above threshold

Emission spectra considerably narrowed in comparison to those at low pumping.

00.511.52

0 0.2 0.4 0.6 0.8 1 1.2Pumping (mJ)Emission (rel. units)

The dependence of the emission intensity shows strongly nonlinear with the distinct threshold.

[Noginov, Zhu, et. al., PRL 2009]

Enhancement of SPs w/o optical gain

Density of states

Energy

EF1

4s

3d

∆E

δE

EF2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

7000 12000 17000 22000 27000 32000

Energy (cm-1)

ε"

594.1 nm

12

34

5

6

7

Trace #1, according to the Drude model

Trace #2, from the first principles for bulk silver;

Traces #3-6, for the surface of silver slabs consisting of

7, 10, 13, and 16 monolayers. .

Modifying surface states of bound electrons Changing Fermi level of a metallic layer

0

0.2

0.4

0.6

0.8

1

1.2

61 63 65 67 69

Angle, θ

R

W1

W2

~ 30% elongation of the

SPP propagation length when the dye conc. is

about 30 g/l !

Elongation of propagation length of SPs –

modify the interface

PMMA film with high concentration of R6G dye was deposited on the silver film.

SPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

EzSPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

EzSPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

Ez

[Zhu, et. al., APL 2009]

[Bobb, Zhu, et. al., APL 2009]

Elongation of propagation length of SPs –

mechanical alloy

0500100015002000

300 800 1300 1800 2300Wavelength, nmPenetration depth lp(nm)

Ag Au lp = λ/20

50

100

150

200

250

300

350

0.4 0.8 1.2 1.6 2

Wavelength, um

Intensity Enhancement

Ag

Au

Plasmonics based on silver and gold

loss their compactness above 539 nm

and 660 nm respectively.

Maximal SPP field

enhancements of silver and

gold centered ONLY around

900nm, very lower at mid-

infrared.

A search for plasmonic materials with higher compactness and efficient

in the infrared, is of high importance.

ld,m =1

Im kd,mz( )

= Imλ

2π

εd +εm

εd,m2

Metal-free plasmonic materials ~ IR range

Metal-free plasmonic materials

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

1200 1400 1600 1800 2000

Wavelength (nm)

Reflectance (rel. units)

0

0.2

0.4

0.6

0.8

1

1

1

2 3

2 3

Heavily doped degenerate wide-band-gap

semiconductors in near-infrared spectral

range with strong confinement of SPPs

and low loss.

-10-8-6-4-2024

800 1300 1800Wavelength, nm

ε,'ε "

ITO

ZITO

AZO

ITZO

Metal-free plasmonic materials-

Semiconductors

0

20

40

60

80

100

0.1 0.2 0.3 0.4 0.5

l d /λ

Qsp

p

1

2

3

4

5

SPP Q-factor on lp/λ for silver (1), gold (2), ITO (3), ZITO (4) and AZO (5).

[Noginov, Gu, Zhu, et. al, OSA 2010, accepted by APL, 2011]

-20

-10

0

10

20

30

40

300 400 500 600 700 800

Wavelength, nm

ε',

ε"

Theoretical predictions

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

300 400 500 600 700 800

Wavelength, nm

ε',

ε"

-1

0

1

2

3

4

5

6

7

300 400 500 600 700 800

Wavelength, nm

ε',

ε"

Kramers-Kronig Relations

)(")('))(

Im())(

Re()(

''

1))'(

Re(1

))(

Im(

''

))'(

Im(1

1))(

Re(

00

0

0

0

0

ωεωεε

ωε

ε

ωεωε

ωωω

ε

ωε

πε

ωε

ωωω

ε

ωε

πε

ωε

ii

dP

dP

+=+=

−

−

−=

−+=

∫

∫

∞

∞−

∞

∞−

Increase of peak absorption leads to negative permittivity

εεεε’<0

εεεε’< 0and

εεεε”~ 0

Experimental samples: Films of several laser dyes

Films preparation:

Dissolved in a solvent

Deposited onto a glass substrate

Dried to a solid state.

Thickness of the film

Film thickness45nm -180 nm

(Dektak-6M profilometer)

Rhodamine-6G film

Rhodamine-6G

(C28H31N2O3Cl) Zn-TPP

HITC (C29H33N2I)

Reflection and transmission spectra

00.050.10.150.20.250.30.350.40.450.5

300 500 700 900 1100 1300Wavelength, nmR

00.10.20.30.40.50.60.70.80.91

300 500 700 900 1100 1300Wavelength, nmT

Reflection is as high as 47% ( λ = 874nm )

HITC film: thickness ~ 63nm

)",'()(;)",'()( 21 εεεεεεεελλλλεεεεεεεελλλλ FTFR ======== ),()(";),()(' 21 RTfRTf ======== λλλλεεεελλλλεεεε

Permittivity (HITC) extracted from R(λλλλ) and T (λλλλ)

ε’max = 10.2 at λ = 864nm

ε’min = -0.2 at λ = 606nm

M. Mayy, Zhu, …, Noginov, JAP, 2009

-10123456789

300 500 700 900 1100 1300wavelength, nm

ε"

ε’’max = 7.98 at λ = 844nm

-202468

1012

300 500 700 900 1100 1300Wavelength, nm

ε '

Permittivity (HITC) extracted from R(λλλλ) and T (λλλλ)

-10123456789

300 500 700 900 1100 1300wavelength, nm

ε"

ε’max = 10.2 at λ = 864nm

ε’min = -0.2 at λ = 606nm

ε’’max = 7.98 at λ = 844nm

-202468

1012

300 500 700 900 1100 1300Wavelength, nm

ε '

)(")('))(

Im())(

Re()(

''

1))'(

Re(1

))(

Im(

''

))'(

Im(1

1))(

Re(

00

0

0

0

0

ωωωωεεεεωωωωεεεεεεεε

ωωωωεεεε

εεεε

ωωωωεεεεωωωωεεεε

ωωωωωωωωωωωω

εεεε

ωωωωεεεε

ππππεεεε

ωωωωεεεε

ωωωωωωωωωωωω

εεεε

ωωωωεεεε

ππππεεεε

ωωωωεεεε

ii

dP

dP

++++====++++====

−−−−

−−−−

−−−−====

−−−−++++====

∫∫∫∫

∫∫∫∫

∞∞∞∞

∞∞∞∞−−−−

∞∞∞∞

∞∞∞∞−−−−

-10123456789

300 500 700 900 1100 1300wavelength, nm

ε"

Permittivity (HITC) extracted from R(λλλλ) and T (λλλλ)

-202468

1012

300 500 700 900 1100 1300Wavelength, nm

ε '

ε’max = 10.2 at λ = 864nm

ε’min = -0.2 at λ = 606nm

ε’’max = 7.98 at λ = 844nm

)(")('))(

Im())(

Re()(

''

1))'(

Re(1

))(

Im(

''

))'(

Im(1

1))(

Re(

00

0

0

0

0

ωωωωεεεεωωωωεεεεεεεε

ωωωωεεεε

εεεε

ωωωωεεεεωωωωεεεε

ωωωωωωωωωωωω

εεεε

ωωωωεεεε

ππππεεεε

ωωωωεεεε

ωωωωωωωωωωωω

εεεε

ωωωωεεεε

ππππεεεε

ωωωωεεεε

ii

dP

dP

++++====++++====

−−−−

−−−−

−−−−====

−−−−++++====

∫∫∫∫

∫∫∫∫

∞∞∞∞

∞∞∞∞−−−−

∞∞∞∞

∞∞∞∞−−−−

Red line – K-K calculations

[M. Mayy, Zhu, et. al., JAP, 2009]

Zn-TPP Dye

0

0.2

0.4

0.6

0.8

1

300 500 700

Wavelength, nm

T

0

5E-16

1E-15

1.5E-15

2E-15

2.5E-15

3E-15

350 450 550 650 750 850

Wavelength, nm

Abs. cro

ss-s

ection, cm

2

1

Zn-TPP

R6G

HITC

ε’ZnTPP(λ=434 nm) = -1.8

0

0.1

0.2

0.3

0.4

0.5

300 500 700

Wavelength, nm

R

R(λλλλ) and T(λλλλ) of Zn-TPP

ε’ZnTPP(λ)

-3

-1

1

3

5

7

9

350 450 550 650 750

Wavelength, nm

ε'

Green – Extracted from T,R

Pink –calculation

SPP excited in ZnTPP

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

30 35 40 45 50 55 60 65

Angle

R

SPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

EzSPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

EzSPPεεεε2

εεεε1

εεεε0

θ0

SPP x

z

Ez

Zn-TPP film

λ λ λ λ = 426nm

Squares: Experiment result

Solid line : Fitting

εεεε1 = -2.6+1.9i

Air

Glass prism

λ λ λ λ = 426nm

-2-101234567

100 300 500 700 900Wavelength, nm

ε'

Dye film with gain ----- Predictions

-8-7-6-5-4-3-2-10

100 300 500 700 900Wavelength, nm

ε"

In the presence of pumping, the dye film

shows emission rather than absorption.

“Metal” with gainUnique properties Fantastic applications

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

350 550 750 950

Wavelength, nm

ε'

AF455

0

0.2

0.4

0.6

0.8

1

360 460 560 660 760 860 960

Wavelength, nm

T

0

0.05

0.1

0.15

0.2

0.25

360 460 560 660 760 860 960

Wavelength, nm

R

C138H174N6

Extracted ε’ from R,T

Dye molecules separated by

alkyl side chains

G.S. He, et al., Chem. Mater. 16, pp.185-194 (2004).

H. Kasai, et al.,.” Jpn. J. Appl. Phys., Part 2 31, L1132 (1992).

6000

8000

10000

12000

14000

16000

18000

320 330 340 350 360

Wavelength, nmE

mis

sio

n r

el. u

nit

Spectroscopy study of AF455 solution

0

0.2

0.4

0.6

0.8

1

250 350 450 550 650

Wavelength, nm

Norm

aliz

ed

Inte

nsity

Extinction

ExcitationEmission

Scattering

Pumped @ 300nm

Emission

Size distribution

Transmission/Scattering with optical pumping

ττττσσσσ

ωωωω

σσσσωωωω

1)(

*

++++⋅⋅⋅⋅

⋅⋅⋅⋅====

abs

abs

sh

Psh

P

PN

n

AF455

dye

Laser radiation

~ 426 nm

Detector #1

(Transmission)

Detector #2

(Scattering)

Normalized Scattering

Normalized Transmission

0

0.5

1

1.5

2

2.5

3

0.001 0.01 0.1 1

Pumping density (mJ/mm2)

Sig

nal (r

el.units)

op

Ground state polulation

Summary

(1) Complete compensation of the SPP loss by gain

(2) Stimulated emission of SPPs and Spaser

nanolaser

(3) Enhancement of SPPs without gain

(4) Metal-free plamonics

active plasmonics matematerials

The results pave the road to many practical

applications of nanoplasmonics and

metamaterials