Lecture 8: Laser amplifiers
Lecture 8: Laser amplifiers
Lecture 8: Laser amplifiers
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Theory of laser amplification<br />
<br />
<br />
<br />
A monochromatic optical plane wave traveling in the z<br />
direction with frequency , electric field<br />
Intensity<br />
E( z)<br />
Re[ E(<br />
z)exp(<br />
i2t<br />
)]<br />
I( z)<br />
|<br />
E(<br />
z)<br />
Photon-flux density (photons per second per unit area)<br />
2<br />
|<br />
<br />
<br />
( z ) I(<br />
z)<br />
/ h<br />
Consider the atomic medium (gain or active medium) with<br />
two relevant energy levels whose energy difference nearly<br />
matches the photon energy h.<br />
The numbers of atoms per unit volume in the lower and upper<br />
energy levels are denoted N 1 and N 2 . (assume g 1 = g 2 )<br />
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