Lecture 8: Laser amplifiers

Quasi-two-level systems
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pump
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However, many laser gain media including laser dyes,
semiconductor gain media, and some solid-state gain media,
are often pumped as a quasi-two-level system.
An energy level is split into a band of closely spaced, but not
exactly degenerate, sublevels with its population density
unevenly distributed among these sublevels.
A system is a quasi-two-level system if either or both of the
two levels involved are split in such a manner.
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