Enhanced optical activity Enhanced optical activity in planar - - PowerPoint PPT Presentation

Makoto Makoto Kuwata Kuwata-

• Gonokami

Gonokami

Department of Applied Physics, University of Tokyo Department of Applied Physics, University of Tokyo CREST CREST, Japan Science and Technology Agency (JST) , Japan Science and Technology Agency (JST) http://www.gono.t.u http://www.gono.t.u-

• tokyo.ac.jp

tokyo.ac.jp

JST-DFG workshop on Nanoelectronics, 05-07.03.2008 in Aachen

Enhanced optical activity Enhanced optical activity in planar in planar chiral chiral nano nano-

• gratings

gratings

• Univ. of Tokyo
• Univ. of Tokyo

Kuniaki Konishi Natsuki Kanda Nobuyoshi Saito Tomohiro Sugimoto Yusuke Ino

• Univ. of
• Univ. of Joensuu

Joensuu

Yuri Svirko Jari Turunen Benfeng Bai Konstantins Jefimovs Tuomas Vallius

Tampere University

Tampere University

Martti Kauranen

Co Co-

• workers

workers

Gonokami Lab. Gonokami Lab.

Optical property of materials Optical property of materials

~1Å＝10-8m

Atom ・ Molecules

0.5μm=500nm

λ

Artificial structures

Gonokami Lab. Gonokami Lab.

n ： Refractive index α： absorption coefficient

Control of optical property with artificial structures Control of optical property with artificial structures

Photonic crystal Ultra high-Q cavity Slow light Metamaterial Negative index Perfect lens 2D metal structure Extraordinary transmission Polarization rotation with chirality

Polarization control with planar chiral nano-gratings

Chirality and Optical activity Optical activity with 2D metal gratings Mechanism of giant optical activity Application for the THz region Future prospect ～Chiral photonic crystal

Outline Outline

Gonokami Lab. Gonokami Lab.

Polarization rotation in Polarization rotation in chiral chiral media media

Chirality Chirality : The existence of the two forms with different handedness Optical activity Optical activity

D = ˜ ε E + ig' k × E

( )

First-order spatial dispersion effect Dependence of wave vector

, k j jk k jki k k i i

E D E x ε γ ∂ = + +⋅⋅⋅ ∂

∑ ∑

Non Non-

• locality of optical response

locality of optical response

Theory microscopic theory : Born (1915)

second order term of dispersion arizing from retardation of radiation

pair of anisotropic dispersion oscillators: Kuhn (1929) quantum-mechanical theory: Rosenfeld (1928) polarizability theory: Gray(1916), de Mallemann(1927), Boys(1934) Discovery 1811 D.F. Arago quartz crystal 1815 J. B. Biot Turpentine oil

Optical activity Optical activity

Polarization control with planar chiral nano-gratings

Chirality and Optical activity Optical activity with 2D metal gratings Mechanism of giant optical activity Application for the THz region Future prospect ～Chiral photonic crystal

Outline Outline

Gonokami Lab. Gonokami Lab.

Polarization Polarization-

• sensitive diffraction in a

sensitive diffraction in a chiral chiral grating grating

• A. Papakostas et al, Phys. Rev. Lett. 90, 107404（2003）

Nonreciprocal polarization rotation?

2D periodic grating of structures without mirror symmetry Diffracted reflection beam shows polarization rotation.

Right-twisted Left-twisted Sense of twist changes Sense of twist changes depending on the incident direction. depending on the incident direction.

Gonokami Lab. Gonokami Lab.

Optical activity with 2D Optical activity with 2D chirality chirality ?? ??

Giant Optical Activity in Metal Giant Optical Activity in Metal nanogratings nanogratings

Giant optical activity

(～104deg/ mm)

• T. Vallius et al., Appl. Phys. Lett. 83, 234 (2003)

M.Kuwata-Gonokami et al., Phys. Rev. Lett. 95, 227401 (2005)

chiral m etal nanogratings 500nm

Cr：23nm Au ：95nm Cr：3nm Silica substrate

Experimental setup Experimental setup

Intensity (transmissivity) Ellipticity angle Polarization azimuth angle

I( 2 p ) I( p ) A , H B I(0 ) I(0 ) Δ = =

Polarization modulation technique*

(modulation frequency: ~50kHz)

Detection limit : ～0.002 degree

*K. Sato,,” Jpn. J. Appl. Phys. 20, 2403 (1981)

θ Α⊿

A sin( 2 B )

Δ Δ

Δ θ ϕ = + +

H H

H A sin( 2 B ) η ϕ = + +

Birefringence

caused by the non-equivalence

• f the X- and Y-axes

Polarization effect due to the specific sense of twist

(independent of ϕ)

At normal incidence

D Distinguish istinguish o

• ptical activity

ptical activity from from birefringence birefringence at at normal incidence normal incidence

Incident direction dependence

Right

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5 Angle [deg] 800 700 600 Wavelength [nm]

Light incidence from front side from back side

From front side From back side Left (chiral) Right (chiral) Cross (achiral)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5 Polarization azimuth rotation θ [deg] 800 700 600 500 Wavelength [nm] θL θA θR

Polarization rotation

M.Kuwata-Gonokami et al., Phys. Rev. Lett. 95, 227401 (2005)

Chirality-induced Giant optical activity

Giant Optical Activity in Metal Giant Optical Activity in Metal nanogratings nanogratings

～1 0 4 deg./ m m

Polarization control with planar chiral nano-gratings

Chirality and Optical activity Optical activity with 2D metal gratings Mechanism of the giant optical activity Application for the THz region Future prospect ～Chiral photonic crystal

Outline Outline

Gonokami Lab. Gonokami Lab.

Optical activity with double Optical activity with double-

• layered structures

layered structures

• M. Decker et. al. Opt. Lett. 32, 856-858 (2007)

MgF2 Au Au 274nm

• E. Plum et. al. Appl. Phys. Lett.

90, 223113 (2007)

Optical activity

• f single-layer structure

is negligible?

Objective Objective

To clarify the mechanism of giant optical activity of single-layer chiral metal nanogratings ＊Calculation of the electric field distribution at the metal surface ＊Measurement of the transmission and polarization rotation spectra at oblique incidence

1 1 m x x m

k iG c ε ε ω ε ε = ± +

p

ω

s

ω

1 1 m x m

k c ε ε ω ε ε = +

L

2 G L π =

sin ck ω θ = Metal x

m

y ε

1

ε

Excitation of surface Excitation of surface plasmon plasmon

Gonokami Lab. Gonokami Lab.

Calculation of the electric field Calculation of the electric field

Y-polarization 752nm

Metal-Substrate interface

500nm

Air-Metal interface

X Y

Calculation method:

• B. Bai and L. Li,
• J. Opt. A: Pure Appl. Opt.

7, 783 (2005)

101×101 grid

( ) ( ) ( ) ( )

( ) χ γ = + ∇× ⎡ ⎤ ⎣ ⎦ P r r E r r E r

Light Light-

• matter coupling in non

matter coupling in non-

• local media

local media

Polarization with first-order spatial dispersion effect

nonlocal

U ≡

( ) ( ) [ ]

( )

d d d

U dz dz dz χ γ = = ⋅ + ∇×

∫ ∫ ∫

EP E E E E

Light-matter coupling energy Electric field strength at the interfaces

( ) ( )

/ 1 2 / 1 2 d d

z e z d e

δ δ − −

= = + = = + E E E E E E

d

Metal Sub.

E1 E2 ( ) ( ) ( ) ( )

{ }

[ ]

(0) ( ) ( , )

nonlocal y air sub x y x

U f d E E d E d E d δ = − ∝ ⋅ × n E E

Eair Esub

[ ]

{ }

( 0) ( ) Re

air sub air sub air sub x y y x

z z d E E E E ⋅ = × = = − n E E

Non-parallel electric field at both interface

Calculation of the electric field Calculation of the electric field

Cross@7 5 2 nm Left @7 5 2 nm

Incident Polarization

( )

( ) (0) ( )

air sub

r d ξ = ⋅ × n E E

0.016 0.016 0.000 0.000 0.011 0.011

• 0.011
• 0.011

≠

total

=

total Dependenc Dependence e of

• f the

the Chirality Chirality factor on the morphology factor on the morphology

Measurement at oblique Measurement at oblique incedence incedence

We measured the transmission and polarization azimuth rotation at oblique incidence

( )

( ) Asin 2 sin(4 ) B C D ϕ θ ϕ ϕ Δ = + + + +

Fitting function ＠720nm

Incident angle ψ＝0° ψ＝+ 3° ψ＝+ 7°

D Distinguish istinguish o

• ptical activity

ptical activity from from birefringence birefringence at at

• blique incidence
• blique incidence

2 4 6 8 10 12 600 700 800 900

• 8
• 6
• 4
• 2

0 2 4 6 8

Transmittance (%)

W a v e l e n g t h ( n m ) Incident angle (deg.)

2 4 6 8 10 12 14 600 700 800 900

• 8
• 6
• 4
• 2

0 2 4 6 8

Transmittance (%)

Wavelength (nm) Incident angle (deg.)

Transmission spectra Transmission spectra

p-polarization s-polarization

1 sp 1 m x x y m

i j c εε ω ε ε = = ± ± + k k G G

Surface plasmon resonance condition

2 2

2 i j + =

2 2 1

i j + =

2 2

2 i j + =

2 2 1

i j + =

1 sp 1 m x x y m

i j c εε ω ε ε = = ± ± + k k G G

Surface plasmon resonance condition

2 4 6 8 10 12 600 700 800 900

• 8
• 6
• 4
• 2

0 2 4 6 8

Transmittance (%)

W a v e l e n g t h ( n m ) Incident angle (deg.)

2 4 6 8 10 12 14 600 700 800 900

• 8
• 6
• 4
• 2

0 2 4 6 8

Transmittance (%)

Wavelength (nm) Incident angle (deg.)

p-polarization s-polarization

2 1 2 2 1 2

( ) sin ( )

s s s

a

ψ ψ ψ

λ ε λ ε ψ ε λ ε ⎛ ⎞ = − ⎜ ⎟ ⎜ ⎟ + ⎝ ⎠

1 2 1 2

( ) sin ( )

p p p

a

ψ ψ ψ

λ ε λ ε ψ ε λ ε = ± +

E E

Transmission spectra Transmission spectra

2 4 6 8 10 12 600 700 800 900

• 8
• 6
• 4
• 2

0 2 4 6 8

Transmittance (%)

W a v e l e n g t h ( n m ) Incident angle (deg.)

• 4
• 2

2 600 700 800 900

• 8
• 6
• 4
• 2

0 2 4 6 8

Polarization azimuth rotatin (deg.) Wavelength (nm) Incident angle (deg.)

C Comparison

• mparison between Transmission

between Transmission and and Polariza Polarizatio tion rotation n rotation spectra spectra

Transmission Polarization rotation

p-polarization p-polarization

kx (1/nm)

• 0.0015
• 0.0010
• 0.0005

0.0000 0.0005 0.0010 0.0015

Energy (eV) 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 kx (1/nm)

• .

1 5

• .

1

• .

5 . . 5 . 1 . 1 5

Energy (eV) 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2

Polarization control with planar chiral nano-gratings

Chirality and Optical activity Optical activity with 2D metal gratings Mechanism of giant optical activity Application for the THz region Future prospect ～Chiral photonic crystal

Outline Outline

Gonokami Lab. Gonokami Lab.

400 500 600 700nm

THz

1015 1μm

1mm 1012

109 1m 1010 1011 1014 1013 10cm 1cm 100μm 10μm 100nm 1016 frequency (Hz)

Electronics

wave length

Electronics Photonics Photonics

The THz region The THz region

Semiconductors, Dielectrics, Superconductivity, Bioscience, …

Application to the THz region Application to the THz region

In the THz region, the metal thickness is much smaller than wavelength. ⇒ Field twist parameter is small.

100μm side view

Si substrate Au 100 nm

complimentary double-layered structure

In complimentary structures, resonances are observed at same frequency (Babinet’s principle)

THz polarization rotation THz polarization rotation with complimentary with complimentary chiral chiral metal gratings metal gratings

0.6 0.4 0.2 0.0 Transmittance 2.0 1.5 1.0 0.5 Frequency (THz)

posi nega

Period: 100μm

Ex

sam

Ex component correspond to polarization rotation

THz polarization rotation THz polarization rotation with complimentary with complimentary chiral chiral metal gratings metal gratings

permittivity polarization rotation

THz polarization rotation THz polarization rotation with complimentary with complimentary chiral chiral metal gratings metal gratings

Summary Summary

We visualized the relationship between surface plasmon resonance and the optical activity of chiral nanogratings. We demonstrated that the chirality can be quantitatively described with the field twist parameter: We demonstrated the polarization rotation of THz waves with complimentary double-layered chiral structures. micro printing techniques such as ink-jet printing

( )

2 unit cell

1

air sub dxdy

A ⋅ ×

∫ n E

E E

・K. Konishi, T. Sugimoto, B. Bai, Y. Svirko, and M. Kuwata-Gonokami , Opt. Express 15, 9575-9583 (2007). Effect of surface plasmon resonance on the optical activity of chiral metal nanogratings ・N. Kanda, K. Konishi, and M. Kuwata-Gonokami, Opt. Ex. 15, 11117 (2007) Terahertz wave polarization rotation with double layered metal grating of complimentary chiral patterns

Polarization control with planar chiral nano-gratings

Chirality and Optical activity Optical activity with 2D metal gratings Mechanism of giant optical activity Application for the THz region Future prospect ～Chiral photonic crystal

Outline Outline

Gonokami Lab. Gonokami Lab.

Future prospect Future prospect

• larger rotation
• higher transmittance
• smaller birefringence

16 14 12 10 8 6 4 Transmission (%) 900 850 800 750 700 650 600 550 Wavelength (nm) Right Left Achiral

2.0 1.5 1.0 0.5 0.0

• 0.5
• 1.0

Polarization rotation [deg.] 150 100 50 Input polarization azimuth [deg.] measurement point sincurve fitting

• ffset

Optical activity

Left＠575nm

Transmittance

Dielectric chiral nanograteng （2 D chiral pthotonic crystal）

birefringence

Gonokami Lab. Gonokami Lab.

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