ECE615_Lecture_25

ECE615_Lecture_25 - (1 Saturation Spectroscopy setup One...

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Unformatted text preview: (1) Saturation Spectroscopy setup: One determines how the response of the medium to the probe wave is modified by the presence of the pump wave. Lecture 25 Optical Wave Mixing in Two-Level Systems strong pump weak probe ϖ ϖ δ + ϖ δ + measure transmission of probe wave atomic vapor (2) Multiwave mixing 1 strong pump weak probe ϖ ϖ δ + ϖ δ + atomic vapor ϖ δ- ϖ ϖ ϖ δ + ϖ ϖ δ- a b Forward 4-wave mixing (generation of the symmetric sideband at frequency ) ϖ δ- At low intensities of the pump laser: (perturbation theory) absorption and dispersion experienced by the probe wave is somewhat reduced by the presence of the pump ) At high intensities of the pump laser: (perturbation theory is not enough) atomic energy levels are strongly modified => new resonances. 2 pump ( ) I I ϖ δ- ∝ Solution of the Density Matrix Equations for a 2-level Atom in the Presence of Pump and Probe Fields ( 29 exp . . E E c c i t ϖ = +- ɶ- complex dipole amplitude : expectation value 2 bb aa w ρ ρ =- ab ba p μ σ = ( 29 exp . . d p p c c i t ϖ ≡ = +- ɶ ɶ p ɶ 2 2 1 ba i i p p Ew T μ ∆ - =- ɺ ℏ ( 29 * 1 4 Im eq w w w pE T- = + ɺ ℏ Solution: exact for the field and the lowest order in the amplitude the steady-state solution is in the form: e solution when only the pump field is present ba w w ∆ =- ( 29 1 exp E E E i t δ = +- E 1 E ( 29 ( 29 1 1 exp exp p p p p i t i t δ δ- = + +- ( 29 ( 29 1 1 exp exp w w w w i t i t δ δ- = + +- w [ ] ( 29 [ ] 1 ( ) exp exp . . E t E E c c i t i t ϖ ϖ δ = + +-- + ɶ 1 E E ≪- the solution when only the pump field is present oscillations of the pump-probe frequency difference...
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ECE615_Lecture_25 - (1 Saturation Spectroscopy setup One...

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