Self-Induced Transparency

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 • 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

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. Conclusion • Self-induced transparency works!