Confusion about Homogenous Broadening in Lasers

[H_man]

In the book I am currently reading one of the causes stated for homogenous broadening in lasers is the ".. finite lifetime of the emitting state".

Now this really confuses me because I would have thought that that a change in the time it takes for this spontaneous emission should affect the phase of the emitting wave relative to other waves present, but I can't see why it would affect the frequency?

I'd also like to clarify a second point. When we have a laser which begins operation and initially generates a homogenously broadened waveform, is mode pulling when the gain in the central frequency rises higher than the other resonant frequencies, and as a result the other frequencies will die down leaving only the single resonant frequency after some short time interval?

I really appreciate the help!

Harry

 

[Andy Resnick]

I think of homogeneous broadening as physical effects that affect all of the atoms: excited state lifetime, pressure (in a gas laser), etc. Inhomogeneous broadening effects are those that affect subpopulations of atoms differently- Doppler boradening, for example.

For the excited state lifetime mechanism, it's really due to the fact that an uncertainty in the time an atom can stay in the excited state is equivalent to an uncertantly in the frequency of the emitted photon.

As for your second question, I've forgotten what mode pulling means... I'll check Siegman's book, see what he says.

 

[H_man]

Thanks, that's very helpful!