Lecture 8: Laser amplifiers
Lecture 8: Laser amplifiers
Lecture 8: Laser amplifiers
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Two-level systems<br />
<br />
<br />
No matter how a true two-level system is pumped, it is not<br />
possible to achieve population inversion for an optical gain<br />
in the steady state.<br />
The optical pump for a two-level system has to be in<br />
resonance with the transition between the two levels –<br />
inducing both downward and upward transitions.<br />
|2><br />
pump<br />
h p<br />
h p<br />
<br />
While a pumping mechanism excites atoms from the lower<br />
energy level to the upper energy level, the same pump also<br />
stimulates atoms in the upper energy level to relax to the<br />
lower energy level.<br />
|1><br />
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