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Lecture 8: Laser amplifiers

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Gain coefficient<br />

<br />

<br />

Consider the incremental number of photons per unit area per<br />

unit time, d(z), is the number of photons gained per unit<br />

time per unit volume, NW i , multiplied by the thickness dz<br />

d<br />

<br />

NW dz<br />

In the form of a differential equation<br />

d<br />

dz<br />

( ) (<br />

z)<br />

i<br />

)<br />

where the gain coefficient<br />

2<br />

c<br />

( ) N<br />

( ) N<br />

2 2<br />

8n<br />

<br />

sp<br />

gˆ(<br />

<br />

78

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