ECE615_Lecture02

ECE615_Lecture02 - Lecture 2 Third-Order Polarization...

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Unformatted text preview: Lecture 2 Third-Order Polarization Third-Harmonic Generation (THG) (1) (2) Energy-level description Geometry of the interaction 1 t t (3) (3) 3 ( ) ( ) P t E t = t ( ) cos( ) . . i t E t t e c c - = = + 3 3 1 4 4 cos ( ) cos3 cos t t t = + t (3) (3) 3 (3) 3 3 1 4 4 ( ) cos3 cos P t t t = + 3 (3) 3 2 Intensity-Dependent Refractive Index 2 nd term in (2) is nonlinear contribution to refractive index n experienced by a wave at . Represented as: Where: = linear refractive index = nonlinear refractive index = intensity of the incident wave 2 n n n I = + n (3) 2 2 3 2 n n c = 2 1 2 I n c = 3- Bulk material then acts as a positive lens, causing the beam to converge.- Self-focusing can cause optical damage. nonuniform transverse intensity distribution positive lens nonlinear material Self-focusing A nonuniform intensity cross-section beam (e.g. Gaussian beam) through a nonlinear refractive index material, results in an increased refractive index for the high intensity regions of the beam....
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ECE615_Lecture02 - Lecture 2 Third-Order Polarization...

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