Self-Induced Transparency By Christine Tsai Physics 138 Presentation

Outline Introduction Features Experiments Conclusion

Introduction Two-level system –Absorption –Spontaneous emission –Stimulated emission

Absorption

Spontaneous Emission

Stimulated Emission

For Self-Induced Transparency… No (small) spontaneous emission Resonant light pulse

So if we shine a light pulse onto an absorptive medium, we’ll get a “population” of excited atoms.

What you will need: Light Pulse and Absorber

Outline Introduction Features Experiments Conclusion

3 Main Features Loss-less propagation Pulse reshaping Pulse delay

Feature #1: Loss-less Propagation Energy is conserved –E input = E output 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

Feature #2: Pulse Reshaping Area Theorem: dA(z)/dz = -  /2 sin[A(z)]

Feature #2: Pulse Reshaping The output pulse may be reshaped by the medium if the input pulse is not SYMMETRIC HYPERBOLIC SECANT.

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 absorber v = velocity of pulse c = speed of light

Outline Introduction Features Experiments Conclusion

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

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:

Gibbs and Slusher Used Hg II laser for input pulses. Used dilute Rb vapor as absorber. Result:

More Results from Gibbs and Slusher:

Outline Introduction Features Experiments Conclusion

Self-induced transparency works!