1. Self-Induced Transparency By Christine Tsai Physics 138 Presentation

2. Outline Introduction Features Experiments Conclusion

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

4. Absorption

5. Spontaneous Emission

6. Stimulated Emission

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

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

9. What you will need: Light Pulse and Absorber

11. Outline Introduction Features Experiments Conclusion

12. 3 Main Features Loss-less propagation Pulse reshaping Pulse delay

13. 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

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

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

16. 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

17. Outline Introduction Features Experiments Conclusion

18. 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

19. 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:

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

21. More Results from Gibbs and Slusher:

22. Outline Introduction Features Experiments Conclusion

23. Self-induced transparency works!