Lecture 4 - Light Interaction with Small Structures

Lecture 4 - Light Interaction with Small Structures -...

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Unformatted text preview: Insulators Rayleigh Scattering (blue sky) Semiconductors.... Resonance absorption at E GAP , size dependent fluorescence) etals esonance absorption at surface plasmon frequency, no light emission) Nanoparticles Light scattering due to harmonically driven dipole oscillator Light Interaction with Small Structures Molecules Microparticles Particles with dimensions on the order of or bigger Metals Resonance absorption at surface plasmon frequency, no light emission) Enhanced forward scattering Applications: resonators, lasers, etc Intuitive ray-picture useful Rainbows due to dispersion H 2 Light Interaction with a Small Object Electric field drives harmonic motion of electrons Consider the Lorentz model e- , 2 2 2 1 L e m i =-- p E tomic polarizability Nucleus + ~ Atomic polarizability Oscillating charges radiates This radiation is the scattered light intensity What does this process look like? +- E H Oscillating charges Emits EM Waves +- E and H fields from oscillating charges E-field lines start at positive charge E-field lines end at negative charge E-field lines close upon themselves (field lines cannot cross) The start of an EM wave After several periods Radiation mainly to oscillation direction Oscillating charges Emit EM Waves Radiation is angle dependent Radiated intensity: 2 4 2 2 3 2 sin 32 p I c r = Derivation: Feynman lectures on physics (or Ramo, et al) p Radiated pattern: Total scattered radiation: 2 4 3 ' 12 S A p P IdA c = = Closed surface around the dipole Radiation Emitted by a Lorentz Oscillator Scattered intensity from a Lorentz Oscillator 2 2 2 1 L e m i =-- p E Scattered intensity by a dipole: 2 4 2 2 3 2 sin 32 p I c r = Lorentz model: 2 4 Lorentz model: 4 4 2 2 2 2 3 2 2...
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Lecture 4 - Light Interaction with Small Structures -...

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