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Re: More laser thoughts




Another idea I worked out on my own, but have yet to encounter elsewhere.
Is this because I'm wrong?

Q: Why is a population inversion necessary in laser material?

A: Because without a population inversion, the laser material acts as
an absorber. When the population inverts, the laser material changes
from 99% transmitting to 101% transmitting.



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I'll confirm that as another laser jock (and from a few written sources I
have around here somewhere). Basically we are looking at gain. Normal
population means most atoms will absorb, inverted population means most will
lead to emission (bear with me on generalizations).

I like to explain it to my students in a pseudo-statistical picture. If you
have a million atoms and 999,990 are not excited then a wandering photon is
most likely to hit a ground state/lower energy level atom and be absorbed.
But if you have a million atoms and 999,990 are excited, then the reverse is
true. I know its overly simplified but it helps the visualization process.
By the way, we can rough out the process mathematically by saying the power
radiated by stimulated emission (P) is expressed by

P = hfNBr

where,

h is PLank's constant
f is frequency
N number of excited atoms
B proportionality constant related to strength of induced transmissions
r is energy density of inducing field

R. Allen Shotwell
Chair, Science and Math
Ivy Tech State College
Terre Haute, IN