ECE615_Lecture08

# ECE615_Lecture08 - Lecture 8 The Wave Equation for...

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Unformatted text preview: Lecture 8 The Wave Equation for Nonlinear Optical Media Laser field induces polarization at new frequency components. Generation of new components are described by Maxwell’s equations. dipole radiation pattern 1 ϖ 2 ϖ 1 2 ϖ ϖ + 1 2 ϖ ϖ + 3 1 2 ϖ ϖ ϖ = + 1 N atoms: if the relative phasing of the dipoles is correct, the field radiation by each dipole will add constructively in the forward direction, leading to radiation in the form of a well-defined beam. Acts as a phased array of dipoles if the phase-matching condition is satisfied. Forward intensity is N 2 larger than single atom. 1 2 ϖ ϖ + Consider a second-order NL process such as sum-frequency generation (SFG). Maxwell’s Equations (omit the arrow sign, for simplicity) (1) (2) (3) (4) D B B E t D H J t ρ ∇⋅ = ∇⋅ = ∂ ∇× = - ∂ ∂ ∇× = + ∂ ɶ ɶ ɶ ɶ ɶ ɶ ɶ = 2 with no free charges and no free currents the material is nonmagnetic (5) Polarization vector ( ) nonlinearly depends on (6) substituting (4), then (5) (7) J ρ = = ɶ B H μ = ɶ ɶ r D E P E ε ε ε = + = ɶ ɶ ɶ ɶ P ɶ E ɶ ( 29 or B E E B t t ∂ ∂ ∇×∇× = ∇× - ∇×∇× = - ∇× ∂ ∂ ɶ ɶ ɶ ɶ 2 2 2 2 2 2 2 2 2 2 2 1 1 1 E D D E P t c t c t c t μ ε ε ∂ ∂ ∂ ∂ ∇×∇× = - = - = -- ∂ ∂ ∂ ∂ ɶ ɶ ɶ ɶ ɶ remember that: but since so so (7) becomes (8) If we define where all nonlinear contributions are in 2 2 2 2 2 2 2 1 1 E E P c t c t ε ∂ ∂ ∇- =...
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## This note was uploaded on 01/10/2011 for the course ECE 615 taught by Professor Shalaev during the Fall '10 term at Purdue.

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ECE615_Lecture08 - Lecture 8 The Wave Equation for...

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