Lecture 8: Laser amplifiers
Lecture 8: Laser amplifiers
Lecture 8: Laser amplifiers
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Three-level pumping<br />
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<br />
Attaining a population inversion N 0 > 0 in the three-level<br />
system requires a pumping rate R > N a /2 sp . A substantial<br />
pump power density given by E 3 N a /2 sp .<br />
The large population in the ground state (which is the lowest<br />
laser level) is an inherent obstacle to attaining a population<br />
inversion in a three-level system that is avoided in a fourlevel<br />
system (in which level 1 is normally empty as 1 is<br />
short).<br />
The saturation time constant s ≈ sp for the four-level<br />
pumping scheme is half that for the three-level scheme.<br />
100<br />
100