Talk:Population inversion

Comments[edit]

Could someone please explain how both the Boltzmann statistics at equilibrium and the population decay rate as per spontaneous emission can both be true? one says the ratio N2/N1 is constant for all times and very small at room temperature, while the other says it goes to to zero exponentially.

The key is in the word "equilibrium". At equilibrium, the Boltzmann statistics apply, and give a (statistically averaged) constant population ratio for all time. If some process places the system in a non-equilibrium (population inversion) state, then the excess population in the high energy state decays exponentially. The given expression does indeed tend to zero - this is an approximation that does not take into account the (rare) reverse transitions that maintain the non-zero Boltzmann equilibrium population ratio. This approximation will be very close to the true ratio until the populations have returned close to their equilibrium ratio.FredV (talk) 01:58, 24 February 2012 (UTC)[reply]

Bulette (talk) 13:54, 23 February 2012 (UTC)[reply]

Population rate equations are missing!

—Preceding unsigned comment added by 134.53.23.204 (talk) 19:26, 21 April 2008 (UTC)[reply]

this might just be me, but i feel that 3 and 4 level lasers deserve their own articles (which, of course, would have links to the population inversion page). also, the "lasing without inversion" link at the bottom of this article is dead

Mmb49 17:50, 11 May 2006 (UTC)[reply]

Perhaps I should have placed all this under laser science, with a pointer at population inversion. You really need to describe it all at once to get the concept across.

Let me know if people find it too impenetrable and/or dumbed-down.

-- DrBob

Very good work. You are also right that population inversion "is a necessary step in the workings of a laser", and that the it could be placed under laser science. And perhaps it is actually better to have a long article explaining all you need to know about lasers. But just keep writing—we can alway reorganize it afterwards. --css

Ok, it's now pretty clear most of this should go in laser science. I'll do so after clarifiying a few more points.

Wrong, it is not. See my writings at laser and Talk:Laser. lysdexia 22:09, 20 Dec 2004 (UTC)

I have removed the disputed tag, since no justification was given. If you wish to reinstate it, please specify which facts you think are inaccurate, here. -- DrBob 22:33, 21 Dec 2004 (UTC)

under spontaneus emession lifetime is not further described. there is neither an entry within wikipedia for it. i would suggest http://en.wikipedia.org/wiki/Mean_lifetime and http://en.wikipedia.org/wiki/Exponential_decay as best explanations, right? Georg

Most of the basics are covered here but I have some simple, colour pics that could be used instead of the text diagrams. There should be no difficulty with copyrights because I drew them originaly! They'll take a while to clean up for use so I'd be grateful for any ideas. Afn

terrible introduction[edit]

starting with 'the concept of population inversion is of fundamental importance' and not explaining the term is a failure to explain what Population inversion means. It would be like starting the article for cotton with 'cotton is of fundamental importance in making a shirt' and omitting from the introduction a simple summary of what cotton is (a soft fibre). Please, somebody who knows what they're talking about, fix this. --81.154.236.221 16:01, 5 October 2005 (UTC)[reply]

I've improved the intro a little. Let me know what you think. -- Bob Mellish 16:41, 5 October 2005 (UTC)[reply]

I think I know what population inversion is now, but I'm really confused, because it doesn't seem to have anything to do with populations or inversions :/ Danielx (talk) 04:30, 24 May 2010 (UTC)[reply]

btw, I did not raise the original complaint. "Terrible" seems a bit harsh, even though "fundamental importance" is not very useful in explaining what population inversion is. Danielx (talk) 04:32, 24 May 2010 (UTC)[reply]

Additional Subject Matter[edit]

I think it would be helpful if there were another paragraph that explained the materials that can produce 3 or 4 energy levels. In addition, how and why do some materials have 3 or 4 energy levels and why are some of the transitions fast and some transistions slow? For some of the explanaition, maybe you could link to another wiki article.

"radiationless"[edit]

In the text it mentions that an electron goes from level 3 to level 2 and no light is emitted ie it is "radiationless". It explains this by "with the energy being transferred to vibrational motion (heat) of the host material surrounding the atoms, without the generation of a photon." I thought this needed some explanation.

john f188.30.24.136 (talk) 09:14, 8 August 2014 (UTC)[reply]

Topic inversion[edit]

Amazing article. A beautiful recounting of the principles behind the operation of a laser. An interesting truth about Wikipedia: the information is there, but it might not be where you look for it. So

Laser story shows up in pop. inversion @misfiled ow.ly/RSTYu

89.217.0.204 (talk) 08:17, 6 February 2015 (UTC)[reply]

Great article[edit]

I just wanted to thank anyone that has contributed to this article for their contribution. Waaaaaaaaay more useful than my professor's notes. Korrector (talk) 23:20, 4 May 2015 (UTC). I couldn't agree more with you. Great explanation! From: Koitus-nlwiki[reply]

Coherence[edit]

From the article: "The critical detail of stimulated emission is that the induced photon has the same frequency and phase as the incident photon. In other words, the two photons are coherent." Do they have the same polarization too?