Finite width of spectral emission lines

Question

Photons nay be emitted from hydrogen at, say 656.28 nm but, I guess in accordance with time-frequency uncertainty, the emission spectrum has a small finite width. This finite width can be wider for emission spectra with shorter decay times, if my understanding is correct.

Spectral emissions are usually given as very precise frequencies. Are these approximations?

See this answer https://physics.stackexchange.com/questions/443054/what-is-the-meaning-of-natural-line-broadening/445731#445731 — , Dec 07 '18 at 15:34
@JulianIngham-- Thank you, it's a very nice answer to this question. — daniel, Dec 07 '18 at 15:36

falgenint · Answer 1 · 2017-04-30T20:05:53.263

0

There exists a "small finite width" for each of the lines of the spectrum due to the uncertainty principle.

What you are describing is called "natural broadening". Other effects which contribute to increase lines width are "Doppler broadening" and "pressure broadening", among others (I'm not taking into account uncertainties due to experimental devices).

As a result you do not obtain a Dirac's delta for each spectral line, but a distribution with some width. You can estimate from it the average frequency.

edited Apr 30 '17 at 20:05

answered Apr 30 '17 at 19:36

falgenint

313

I said the opposite: shorter decay times imply a bigger spread in frequency due to the uncertainty relation. If I'm not mistaken, the spread in frequency can be used to infer the decay time... – daniel Apr 30 '17 at 19:39
Yes, I didn't read that well :) How can you know the decay time if you know the spread in frequency? – falgenint Apr 30 '17 at 19:45
Uncertainty gives that $\Delta f\Delta t \geq k.$ If you have a handle on $\Delta f...$ – daniel Apr 30 '17 at 19:49
I was thinking on other thing... my english is not very well, I'm sorry... but that's it, you are right! – falgenint Apr 30 '17 at 20:05
Is the reported frequency an average? Can you cite a reference? – daniel May 01 '17 at 18:31
You can read this and this. I've also found interesting the answers given here related to your question. – falgenint May 01 '17 at 19:34
Thanks these do seem relevant and I will look them over as soon as I have a moment. – daniel May 01 '17 at 19:58

Finite width of spectral emission lines

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