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Lecture 8: Laser amplifiers

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Rate equations<br />

2<br />

R 2<br />

1/ 21 = 1/ sp + 1/ nr<br />

1<br />

sp<br />

nr<br />

1/ 2 = 1/ 21 + 1/ 20<br />

R 1<br />

1<br />

20<br />

1/ nr<br />

: non-radiative decay rate<br />

<br />

<br />

Steady-state populations of levels 1 and 2 can be maintained only if<br />

the energy levels above level 2 are continuously excited by<br />

pumping and ultimately populate level 2.<br />

Pumping serves to populate level 2 at rate R 2 and depopulate level<br />

1 at rate R 1 (per unit volume per second)<br />

=> levels 1 and 2 can attain non-zero steady-state populations.<br />

85<br />

85

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