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– 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

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 absorberv = velocity of pulsec = 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

Conclusion

• Self-induced transparency works!