Self-Induced Transparency
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Transcript of Self-Induced Transparency
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Self-Induced Transparency
By Christine Tsai
Physics 138 Presentation
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Outline
• Introduction
• Features
• Experiments
• Conclusion
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Introduction
• Two-level system– Absorption– Spontaneous emission– Stimulated emission
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Absorption
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Spontaneous Emission
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Stimulated Emission
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For Self-Induced Transparency…
• No (small) spontaneous emission
• Resonant light pulse
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• So if we shine a light pulse onto an absorptive medium, we’ll get a “population” of excited atoms.
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What you will need:Light Pulse and Absorber
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Outline
• Introduction
• Features
• Experiments
• Conclusion
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3 Main Features
• Loss-less propagation
• Pulse reshaping
• Pulse delay
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Feature #1:Loss-less Propagation
• Energy is conserved– Einput = Eoutput
• No spontaneous decay– Spontaneous decay can go in any direction, so
usually E is lost from the beam. R >> 1/
R = Rabi frequency of input pulse
= life time of atom in excited state
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Feature #2:Pulse Reshaping
• Area Theorem:
dA(z)/dz = -/2 sin[A(z)]
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Feature #2:Pulse Reshaping
• The output pulse may be reshaped by the medium if the input pulse is not SYMMETRIC HYPERBOLIC SECANT.
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Feature #3:Pulse Delay
• As light pulse passed through the absorber, it is delayed.
• Delay time is:
delay = (L/v) – (L/c)L = length of absorberv = velocity of pulsec = speed of light
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Outline
• Introduction
• Features
• Experiments
• Conclusion
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Experiments• Experiments on Self-induced transparency have
been performed by many physicists. And they have confirmed that the effect exists.
• Some people who have done the experiment:– McCall and Hahn– Gibbs and Slusher
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McCall and Hahn• Used a Q-switched liquid-nitrogen-cooled ruby laser to
create short input pulse.
• Used a liquid-helium-cooled ruby rod as the absorber.
• Result:
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Gibbs and Slusher• Used Hg II laser for input pulses.
• Used dilute Rb vapor as absorber.
• Result:
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• More Results from Gibbs and Slusher:
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Outline
• Introduction
• Features
• Experiments• Conclusion
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Conclusion
• Self-induced transparency works!