Q-Han Park

Korea Univ.

APSE 2010

1

The 4th Yamada Symposium on Advanced Photons and Science Evolution 2010

EM field enhancement - antennas

Marconi's antenna system at Poldhu Cornwall, December

1901.

Monopole antenna

Antenna - receiver

Frequency independent antenna

Yagi antenna

Horn antenna

at Bell Labs, Holmdel, NJ that Penzias and Wilson used to discover the 3 K

cosmic microwave background radiation in 1965.

Nano-optical antenna

Radio/microwave

20 C.

Optical antenna

21 C.

1900 1945 21st century

mm

nm

Radar

MarconiRF antanna

: human to human

Opt. Ant.

New frontier: human to nanoworld

NanoopticsSERSCancerLEDSolar cell

:

Cell Phonem

4

Optical antenna-monopole

Optical monopole antenna

Bring it down to the optical regime !

N.F. van Hulst group,

Nano Lett. 7,28, 2006

nature photonics, 2008

Optical antenna - sensor

Optical monopole antenna Single molecule fluorescence

Excitation 514 nm

Fluorescence 570 nm

Emission control by a monopole antenna

Optical antenna as a vector field probe

D.S.Kim, Q.Park. et al, Nature Photonics 1, 53 (2007)

• dipole plasmon resonance Transmission, bio-sensing, cancer therapy

N. Halas group

S.Cho, Q.H.Park, Angew. Chem.Int. 2007

•128 nm core diameter, 14 nm gold shell,

• peak absorbance at 820 nm

• 10 degree Temp increase

Nano metal particles

B.Kim, Q.H.Park, JACS, 2007; JACS 2009

J.Joo, Q.H.Park, Adv. Mater. 2007

SP enhanced PLSERS, silver nanorod+plate

S.W.Han, Q.H.Park, JACS. 2009

Dodecahedron

Metallic nano structures

Optical antenna - bowtie

Bow tie antenna – EUV generation

S.W.Kim et al, Nature 2008

Bow tie antenna

S.W.Kim et al, Nature 2008

Terahertz – nano

Terahertz field enhancement by a metallic nano slitoperating beyond the skin-depth limit D.S.Kim, Q.Park et al.

Nature Photonics 3, 152, 2009

EM field enhancement by nano slit

Electric field enhancement: ~1,000 with λ /10,000 size gap

Diffraction theory claculation

Mordal expansion

/2 /20

0

0

00

/20

0

,

2, cos

,

z z

m m

z

I ikx ik z h ikx ik z hy

II i z i zy m m

m

III ikx ik z hy

H x z dk k e k e

m xH x z A e B e

a

H x z dk k e

22 2 20 0, 2 /z mk k k k m a

0 2 /k

2 20 0 0

0

2 20 0

0

22 2

02 2

m m

m m

h hi i

m m mn mn m m m mn mn m nm

h hi i

m m mn mn m m m mn mn mm

a aA e W B e W a

a aA e W B e W

Boundary matching

Mode Coupling Strength W:

2 20 00

(1)0 00 0

1 2 2cos cos

2

1 2 2cos cos

2

ik x ya a

mn

a a

m x n y eW dx dy dk

a a k k

m x n ydx dy H k x y

a a

Mordal method vs. FDTD numerical method

width = 0.0002 thickness = 0.002

Good quantitative predictions, but only good for global/specific geometry

Ex field at x=a/2, z=h/2

Field enhancement

Local capacitor model

-zone

Local Capacitor Model for Plasmonic Electric Field EnhancementQ.Park Phys. Rev. Lett.102, 093906, 2009

Slit

-zone capacitance

Static capacitance restricted to the -zone

02 vC

,

2

aE t kz t

E k

sint w

0 0

0

1

2

effInd SZ ZQ dA K ndl

iw

iw i

##############

2IndEiav

Conformal mapping

2IndEiav

width = 0.00067 thickness = 0.002

Enhanced electric field inside the gap

Real metal case

Good qualitative agreement

x

y

zy-polarized incident light

Metal tip near metal surface

Intensity profile near metal tip (FDTD calculation:xy-cut)

xz-cut

Bowtie

Spheroidal prolate coordinates Field enhancement

sinh sin cos ,

sinh sin sin ,

cosh cos

x a u v

y a u v

z a u v

Prolate spheroidal coordinates

tip surface: v = v0.

2

2 21 22 2 2 2 2 2

1 2 1 1 1 2 2 2

2

2 22 231 2

1 1 1 11 1

1 1

1 1

a a

a

1 2 3cosh , cos , u v

Static potential

sinh sin cos ,

sinh sin sin ,

cosh cos

x a u v

y a u v

z a u v

Prolate spheroidal coordinates

1 2 3cosh , cos , u v

specify the shape of a hyperboloid tip by v = v0.

22

2 2

1 0

1

01 1

1 cos 1 cosln , ln

1 cos 2 1 cos

Vv vC C

v v

0 1

00

4

cos

CQ d

v

0

0

1

0

0

2 1 cosln

cos 1 cosv

Q vC

v

/2

0/2

/2

0 0/2

0 0

1 ˆ ˆ

2 ˆ ˆ ˆ

4

indQ K n diw

n H n diw

Hiw

0 0

8indQ H

iw

Surface current in the back side

0 0 02

0

2 cos 1 cosln

1 cosind

ind

Q v vE

dC i d v

Induced current/charge

ν0=π/6

0 0 02

0

2 cos 1 cosln

1 cosInd

v vE

i d v

LCM for a metal tip

Slot antenna

/2

Half wave dipole antenna

Slot antenna

EH

Resonantly enhanced radiation

THz slot antenna

Near field imaging of terahertz focusing onto rectangular aperturesD.S.Kim, P. Planken, Q.Park, Optics Express 16,20484, 2008

Fourier transform terahertz imaging of E_x

Energy Funneling: constant energy

Substrate effect on aperture resonances in a thin metal filmJ. H. Kang, J.H. Choe, D.S. Kim, Q. Park, Optics Express 17,15652, 2009

Substrate effect

Substrate effect

ansres 2)75.025.0(

Resonance

23

322

)5.05.0(

)75.025.0(4

4

3

s

ssres n

n

ab

naT

Transmission at resonance

Phased array antenna

X-Band Phased-Array Antenna

r = 100 nm, p = 800 nm, t = 300 nm, Au on sapphire

SEMSEM

Extraordinary Optical TransmissionExtraordinary Optical Transmission

~ 5%!

T. W. Ebbesen et al., Nature 391, 667-669 (1998)

Various slots for terahertz frequencies

SEM or Microscopic Images0.5 mm

At terahertz, metals are lossless: ~1/1000;wavelength: 0.1 mm~10 mm, skin depth=100 nm,

Shape resonance omni-directional terahertzfilters with near-unity transmittanceD.S. Kim et al. Opt. Expr. 14,1253,(2006)

Perfect transmission

Optical Yagi-Uda Antenna

Directional control of light by a nano-optical Yagi–Uda antennaTerukazu Kosako1, Yutaka Kadoya, Holger F. Hofmann, NATURE Photon, March, 2010

Conclusions

Learn from analogies• receive and transmit• enhance and focus electric field• Directivity• Phased array

Learn from differences• can be active -- lasing• nonlinear optical processes• communicates with nano world:

- controlled chemistry/biology• more to come

Photonic crystal, metamaterial, optical antenna,…