JST-DFG workshop on Nanoelectronics, 05-07.03.2008 in Aachen Enhanced optical activity Enhanced optical activity in planar chiral chiral nano nano- -gratings gratings in planar Makoto Kuwata Kuwata- -Gonokami Gonokami Makoto Department of Applied Physics, University of Tokyo Department of Applied Physics, University of Tokyo CREST, Japan Science and Technology Agency (JST) , Japan Science and Technology Agency (JST) CREST http://www.gono.t.u- -tokyo.ac.jp tokyo.ac.jp http://www.gono.t.u
Co- -workers workers Co � Univ. of Univ. of Joensuu Joensuu � � Univ. of Tokyo Univ. of Tokyo � � Yuri Svirko � Kuniaki Konishi � Jari Turunen � Natsuki Kanda � Benfeng Bai � Nobuyoshi Saito � Konstantins Jefimovs � Tomohiro Sugimoto � Tuomas Vallius � Yusuke Ino � Tampere University Tampere University � Martti Kauranen Gonokami Lab. Gonokami Lab.
Optical property of materials Optical property of materials Atom ・ Molecules Artificial structures n ： Refractive index α ： absorption coefficient λ 0.5 μ m=500nm ~1 Å＝ 10 -8 m Gonokami Lab. Gonokami Lab.
Control of optical property with artificial structures Control of optical property with artificial structures Photonic crystal 2D metal structure Metamaterial Negative index Perfect lens Ultra high-Q cavity Slow light Extraordinary transmission Polarization rotation with chirality
Outline Outline 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 Gonokami Lab. Gonokami Lab.
Polarization rotation in chiral chiral media media Polarization rotation in Chirality : The existence of the two forms with different handedness Chirality Optical activity Optical activity
Non- -locality of optical response locality of optical response Non Optical activity Optical activity ∂ E ∑ ∑ = ε + γ +⋅⋅⋅ k D E ∂ j jk k jki x k k i , i First-order spatial dispersion effect ( ) D = ˜ ε E + ig ' k × E Dependence of wave vector Discovery 1811 D.F. Arago quartz crystal 1815 J. B. Biot Turpentine oil 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)
Outline Outline 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 Gonokami Lab. Gonokami Lab.
Polarization- -sensitive diffraction in a sensitive diffraction in a chiral chiral grating grating Polarization A. Papakostas et al, Phys. Rev. Lett. 90 , 107404 （ 2003 ） 2D periodic grating of structures without mirror symmetry Nonreciprocal polarization rotation? Diffracted reflection beam shows polarization rotation.
Optical activity with 2D chirality chirality ?? ?? Optical activity with 2D 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.
Giant Optical Activity in Metal nanogratings nanogratings Giant Optical Activity in Metal 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 Giant optical activity Cr ： 3nm Silica ( ～ 10 4 deg/ mm) substrate
Experimental setup Experimental setup Polarization modulation technique* (modulation frequency: ~50kHz) Intensity (transmissivity) Ellipticity angle Polarization azimuth angle I( 2 p ) I( p ) Δ = = A , H B 0 0 I(0 ) I(0 ) Detection limit : ～ 0.002 degree *K. Sato,, ” Jpn. J. Appl. Phys. 20 , 2403 (1981)
Distinguish istinguish o optical activity ptical activity from from birefringence birefringence at at D normal incidence normal incidence At normal incidence Δ = θ + ϕ + A sin( 2 B ) Δ Δ = η + ϕ + H A sin( 2 B ) H H Birefringence Α ⊿ caused by the non-equivalence of the X- and Y-axes Polarization effect due to the specific sense of twist θ (independent of ϕ )
Giant Optical Activity in Metal nanogratings nanogratings Giant Optical Activity in Metal M.Kuwata-Gonokami et al. , Phys. Rev. Lett. 95 , 227401 (2005) Incident direction Polarization rotation dependence θ [deg] θ L 1.5 1.5 Left Light incidence Right θ A from front side (chiral) 1.0 Polarization azimuth rotation 1.0 from back side θ R Angle [deg] 0.5 0.5 0.0 Cross 0.0 (achiral) -0.5 -0.5 -1.0 -1.0 Right -1.5 ～ 1 0 4 deg./ m m (chiral) -1.5 600 700 800 500 600 700 800 Wavelength [nm] Wavelength [nm] From front side From back side Chirality-induced Giant optical activity
Outline Outline 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 Gonokami Lab. Gonokami Lab.
Optical activity with double- -layered structures layered structures Optical activity with double 274nm Au MgF 2 Au E. Plum et. al. Appl. Phys. Lett. 90, 223113 (2007) Optical activity of single-layer structure is negligible? M. Decker et. al. Opt. Lett. 32, 856-858 (2007)
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
Excitation of surface plasmon plasmon Excitation of surface y x ε 1 ε Metal m L ω = θ ck sin ω p ω s ε ε ω = 1 m k ε + ε x c 1 m π ω ε ε 2 = ± = 1 m k iG G ε + ε x x Gonokami Lab. Gonokami Lab. c L 1 m
Calculation of the electric field Calculation of the electric field Air-Metal interface Y-polarization 752nm Metal-Substrate interface Y Calculation method: 500nm X B. Bai and L. Li, J. Opt. A: Pure Appl. Opt. 101 × 101 grid 7, 783 (2005)
Light- -matter coupling in non matter coupling in non- -local media local media Light Polarization with first-order spatial dispersion effect ( ) ( ) ( ) ( ) = χ + γ ⎡ ∇× ⎤ P r ( ) r E r r ⎣ E r ⎦ Light-matter coupling energy d d d ( ) [ ] ( ) ( ) ∫ ∫ ∫ = = χ ⋅ + γ ∇× U dz dz dz EP E E E E 0 0 0 ≡ U nonlocal Electric field strength at the interfaces E 1 ( ) − δ = = + d / E z 0 E E e 1 2 ( ) − δ = = + d d / Metal E z d E e E 1 2 Sub. E 2 E air { } ( ) ( ) ( ) ( ) = δ − U f d ( , ) E 0 E d E d E 0 nonlocal y x y x [ ] ∝ ⋅ × n E (0) E ( ) d E sub air sub
Calculation of the electric field Calculation of the electric field Non-parallel electric field at both interface [ ] ⋅ = × = = n E ( 0) E ( ) z z d air sub { } − air sub air sub Re E E E E x y y x
Dependence e of of the the Chirality Chirality factor on the morphology factor on the morphology Dependenc ( ) ξ = ⋅ × ( ) r n E (0) E ( ) d air sub Left @7 5 2 nm Cross @7 5 2 nm Incident Polarization total total 0.016 0.000 0.011 -0.011 ≠ = 0 0 0.000 0.016 -0.011 0.011
Measurement at oblique incedence incedence Measurement at oblique We measured the transmission and polarization azimuth rotation at oblique incidence
Distinguish istinguish o optical activity ptical activity from from birefringence birefringence at at D oblique incidence oblique incidence ＠ 720nm Incident angle ψ＝ 0 ° ψ＝ + 3 ° ψ＝ + 7 ° ( ) Δ ϕ = θ + ϕ + + ϕ + Fitting ( ) Asin 2 B C sin(4 D ) function
Transmission spectra Transmission spectra + = + = 2 2 2 2 2 i j i j 2 s-polarization p-polarization 2 1 2 1 + = + = 2 2 i j Transmittance (%) Transmittance (%) i j 14 12 12 10 10 8 8 6 Incident angle (deg.) 6 0 2 4 6 8 0 2 4 6 8 Incident angle (deg.) 4 4 2 2 -2 600 600 -2 -4 700 -4 -6 700 Wavelength (nm) -6 -8 800 W -8 a v 800 e l e 900 n g t h 900 ( n m ) Surface plasmon resonance condition εε ω ε = = ± ± 1 m k k G G i j ε + sp x x y c 1 m
Transmission spectra Transmission spectra s-polarization p-polarization Transmittance (%) Transmittance (%) 14 12 12 10 10 8 8 6 Incident angle (deg.) 6 0 2 4 6 8 0 2 4 6 8 Incident angle (deg.) 4 4 2 2 -2 600 600 -2 -4 700 -4 -6 700 Wavelength (nm) -6 -8 800 W -8 a v 800 e l e 900 n g t h 900 ( n m ) Surface plasmon resonance condition 2 ⎛ ⎞ λ ε λ ε λ ε λ ε E E p p s s ( ) ( ) ψ ψ εε ψ ψ = ± ω ψ = − ψ ⎜ ⎟ 1 2 1 2 2 sin sin ⎜ ⎟ ε λ + ε ε = = ± ± ε λ + ε p s a ( ) 1 m ( ) ⎝ a ⎠ k k G G i j ψ ψ 1 2 1 2 ε + sp x x y c 1 m
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