APSE Q-Han Park Korea Univ.

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1 APSE 2010 Q-Han Park Korea Univ. The 4 th Yamada Symposium on Advanced Photons and Science Evolution 2010

2 EM field enhancement - antennas Monopole antenna Marconi's antenna system at Poldhu Cornwall, December 1901.

3 Antenna - receiver Frequency independent antenna Yagi antenna Horn antenna at Bell Labs, Holmdel, NJ that Penzias an d Wilson used to discover the 3 K cosmic microwave background radiation in 1965.

4 Nano-optical antenna 20 C. Radio/microwave 21 C. Optical antenna st century m Marconi RF antanna Cell Phone Radar New frontier: human to nanoworld mm nm : human to human Opt. Ant. Nanooptics SERS Cancer LED Solar cell :

5 Optical antenna-monopole Bring it down to the optical regime! N.F. van Hulst group, Nano Lett. 7,28, 2006 Optical monopole antenna nature photonics, 2008

6 Optical antenna - sensor Optical monopole antenna Single molecule fluorescence Excitation 514 nm Fluorescence 570 nm Emission control by a monopole antenna

7 Optical antenna as a vector field probe D.S.Kim, Q.Park. et al, Nature Photonics 1, 53 (2007)

8 Nano metal particles dipole plasmon resonance Transmission, bio-sensing, cancer therapy N. Halas group 128 nm core diameter, 14 nm gold shell, peak absorbance at 820 nm 10 degree Temp increase S.Cho, Q.H.Park, Angew. Chem.Int. 2007

9 Metallic nano structures SP enhanced PL SERS, silver nanorod+plate J.Joo, Q.H.Park, Adv. Mater Dodecahedron S.W.Han, Q.H.Park, JACS B.Kim, Q.H.Park, JACS, 2007; JACS 2009

10 Optical antenna - bowtie

11 Bow tie antenna EUV generation S.W.Kim et al, Nature 2008

12 Bow tie antenna S.W.Kim et al, Nature 2008

13 Terahertz nano Terahertz field enhancement by a metallic nano slit operating beyond the skin-depth limit D.S.Kim, Q.Park et al. Nature Photonics 3, 152, 2009

14 EM field enhancement by nano slit Electric field enhancement: ~1,000 with λ /10,000 size gap

15 Diffraction theory claculation Mordal expansion ε ( ) H x z = d k k e + ρ k e ( ) 0 (, ) δ ( ) ( ) 0 (, ) = τ ( ) ( /2) ( ) ( ) I ikx+ ikz z+ h/2 ikx ikz z+ h/2 y µ 0 ε 2mπ x H xz Ae Be ( II ) 0 i mz i mz y (, ) = θ θ cos m + m µ 0 m= 0 a ε H x z dk k e III ikx+ ikz z h y µ m 0 ( π ) 2 k k k, θ k 2 m / a z k0 = 2 π / λ

16 Boundary matching m= 0 m= 0 a a Ae W Be W a 2 2 h h iθm 2 iθm 2 m θm mn + ( δmn + δ0m ) + m θm mn + ( δmn + δ0m ) = 2 δn0 h h iθm 2 a iθm 2 a Ae m θmwmn ( δmn + δ0m ) + Be m θmwmn ( δmn + δ0m ) = Mode Coupling Strength W: ( ) ( y) ik x 1 a a 2mπx 2nπy e Wmn dx dy cos cos dk 2π 0 0 a a k k 1 a a 2mπx 2nπy (1) = dx dy cos cos H k0 x y 2 a a 2 2 0

17 Field enhancement Mordal method vs. FDTD numerical method Ex field at x=a/2, z=h/2 width = thickness = Good quantitative predictions, but only good for global/specific geometry

18 Local capacitor model Local Capacitor Model for Plasmonic Electric Field Enhancement Q.Park Phys. Rev. Lett.102, , 2009 λ-zone

19 Slit λ-zone capacitance Static capacitance restricted to the λ-zone

20 Conformal mapping ( ) z t = (, ) ( ) ae t k 2E k t = sin ( w) Q 1 Ind = σ da S = K eff ndl Z iw Z 2 ε0 ελ 0 = = iw µ iπ C λ = 0 2ε v 0 π λ E Ind = λ 2iav λ

21 Enhanced electric field inside the gap width = thickness = E Ind = λ 2iav λ

22 Real metal case Good qualitative agreement

23 Metal tip near metal surface Intensity profile near metal tip (FDTD calculation:xy-cut) y x z y-polarized incident light xz-cut

24 Bowtie Spheroidal prolate coordinates Field enhancement

25 Static potential Prolate spheroidal coordinates x= asinh usin vcos φ, y = asinh usin vsin φ, z = acosh ucos v tip surface: v = v 0. 2 = ψ ψ ψ ( ξ1 1) ( 1 ξ2 ) a ξ1 ξ2 ξ1 ξ1 a ξ1 ξ2 ξ2 ξ ψ a ( ξ1 1)( 1 ξ2 ) ξ3 1 cosh u, 2 cos v, 3 ξ = ξ = ξ = φ

26 Prolate spheroidal coordinates x= asinh usin vcos φ, y = asinh usin vsin φ, z = acosh ucos v ξ = cosh u, ξ = cos v, ξ = φ specify the shape of a hyperboloid tip by v = v 0. ξ Q λ 2 ψ ( 1 ξ2 ) = 0 ξ 2 2 ψ cos v V0 1+ cos v = C1ln, C1 = ln 1 cos v 2 1 cos v ( ) 4πε 0C1λ Qλ πε 0λ = ε0 ψ dσ = Cλ cos v ψ v cos v 0 = = ln cos 1 cos v0

27 Induced current/charge 1 π /2 Q ( ˆ ˆ) ind = K n /2 0d iw φ ρ φ π 2 π /2 = ρ ˆ ( ˆˆ ( )) 0 φ n H /2 0 n dφ iw π 4 = ρ0h0 iw Surface current in the back side Qind = 8 H iw ρ 0 0 E ind Qind 2ρ0cos v 0 1+ cos v 0 = = ln 2 dcλ iπ d 1 cos v0

28 LCM for a metal tip ν 0 =π/6 E Ind 2ρ0cos v 0 1+ cos v 0 = ln 2 iπ d 1 cos v0

29 Slot antenna Slot antenna Half wave dipole antenna λ/2 H E Resonantly enhanced radiation

30 THz slot antenna Near field imaging of terahertz focusing onto rectangular apertures D.S.Kim, P. Planken, Q.Park, Optics Express 16,20484, 2008

31 Fourier transform terahertz imaging of E_x

32 Energy Funneling: constant energy

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

34 Substrate effect

35 Resonance λ = λ res = ( n s ) 2 Transmission at resonance a T res 3 4a = 4 π 2 ( n ab s ) 2 3 ns ( n 3 s ) 2

36 Phased array antenna X-Band Phased-Array Antenna

37 Extraordinary Optical Transmission Transmission Intensity (a. u.) Air/Au (1, 0) Al 2 O 3 /Au (1, 1) ~ 5%! SEM Wave length (nm) r = 100 nm, p = 800 nm, t = 300 nm, Au on sapphire T. W. Ebbesen et al., Nature 391, (1998)

38 Various slots for terahertz frequencies At terahertz, metals are lossless: δ/λ~1/1000; wavelength: 0.1 mm~10 mm, skin depth=100 nm, Shape resonance omnidirectional terahertz filters with near-unity transmittance D.S. Kim et al. Opt. Expr. 14,1253,(2006) 0.5 mm SEM or Microscopic Images

39 Perfect transmission

40 Optical Yagi-Uda Antenna Directional control of light by a nano-optical Yagi Uda antenna Terukazu Kosako 1, Yutaka Kadoya, Holger F. Hofmann, NATURE Photon, March, 2010

41 Conclusions Photonic crystal, metamaterial, optical antenna, 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

Substrate effect on aperture resonances in a thin metal film

Substrate effect on aperture resonances in a thin metal film J. H. Kang 1, Jong-Ho Choe 1,D.S.Kim 2, Q-Han Park 1, 1 Department of Physics, Korea University, Seoul, 136-71, Korea 2 Department of Physics