Lecture 10 - Surface Plasmon Excitation

# Lecture 10 - Surface Plasmon Excitation - Lecture 10...

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Lecture 10: Surface Plasmon Excitation 5 nm

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Summary Coupling light to surface plasmon-polaritons • Kretchman geometry • Grating coupling 2 //, sin SiO d sp kk c ω εθ = = • Coupling using subwavelength features This lecture: • Using high energy electrons (EELS) The dispersion relation for surface plasmons p sp k • Useful for describing plasmon excitation & propagation • A diversity of guiding geometries E H Θ sp k 2 SiO k
Dispersion Relation Surface-Plasmon Polaritons 1/2 md x k c εε ω ⎛⎞ = ⎜⎟ + ⎝⎠ Plot of the dispersion relation • Last page: • Plot of the dielectric constants: • Low ω : lim m x d k cc ε ωω →−∞ =≈ + • Note: r p sp d d Dielectric Metal x k →∞ x k sp x d k c = Solutions lie below the light line! (guided modes) Light line in dielectric Define: ω = ω sp when ε m = - ε d when ε m = - ε d

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Dispersion Relation Surface-Plasmon Polaritons Dispersion relation bulk and surface plasmons • Note: Higher index medium on metal results in lower ω sp 2 2 1 p md ε =− 22 2 pd ωε −= 2 2 1 p d = + = sp when: Metal/air Metal/dielectric with ε d 1 p d = + , SP Air , d SP
Excitation Surface-Plasmon Polaritons (SPPs) with Light Problem SPP modes lie below the light line • Need a “trick” to excite modes below the light line ω k sp c k = • Excitation SPP at a metal/air interface from a high index medium n = n h h c kn = • SPP at metal/air interface can be excited from a high index medium! Trick 1: Excitation from a high index medium • How does this work in practice ? • No coupling of SPP modes to far field and vice versa (reciprocity theorem) e h k sp k Air k s h p k k >

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Kretchmann geometry (Trick 1) Excitation Surface-Plasmon Polaritons with Light ω k sp c k = c kn = e 2 SiO k sp k Air k • Makes use of SiO 2 prism • Create evanescent wave by TIR • Strong coupling when k //,SiO2 to k sp Note: we are matching energy and momentum • Reflected wave reduced in intensity 2 SiO k 2 //, SiO k sp k From dispersion relation E H θ
Kretchmann geometry Surface-Plasmon is Excited at the Metal/Air Interface • Makes use of SiO 2 prism • Enables excitation surface plasmons at the Air/Metal interface 2 SiO k , s pA i

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• Fall '08
• Staff
• Total internal reflection, Condensed matter physics, Surface plasmon resonance, Excitation Surface-Plasmon Polaritons

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Lecture 10 - Surface Plasmon Excitation - Lecture 10...

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