Talk:Stimulated emission

Untitled
Needs sections. Zack Green 15:57, 12 October 2005 (UTC)

The formula for the emission looks strange: $$ \sigma_{21}(\nu) = A_{21} { \lambda^2 \over 8 \pi n^2} g(\nu) $$

are $$ \lambda $$ and $$\nu$$ independent parameters?

user:Domitori

Needs a History section
This article definitely needs a history section. I mean, this article doesn't even mention Albert Einstein. I don't really know enough about it to write it myself. I just know that Einstein discovered it by accident. ~ Oni Lukos ct 13:50, 30 August 2006 (UTC)


 * In the See also section, I have now added a link to the excellent History section of the Laser article. Yes, it starts with Einstein. Dirac66 (talk) 22:36, 7 February 2010 (UTC)


 * Should we say (per laser) Einsteins motivation was to [better] explain the blackbody radiation distribution ? & Should we call it a 'prediction' rather than a discovery ? - Rod57 (talk) 09:59, 27 February 2017 (UTC)

Quantum mechanical explanation?
The article gives at least a hint of a classical explanation (or justification) for the process -- that the dipole moment induced by the incident photon "encourages" the atom to produce another, identical photon. What is there seems a bit of a lie-to-children, but perhaps I'm mistaken and it's classically accurate. (Thoughts?) Anyway, could someone who understands the "real" picture provide at least that much of an explanation from the quantum mechanical point of view? Thanks. --Tardis 18:26, 21 September 2006 (UTC)


 * Hopefully the quantum mechanical explanation will say why "the second photon is created with the same phase, frequency, polarization, and direction of travel as the original." I suspect it is due to constructive interference, and might only be true on the macroscale. Someone know for sure? --Michael C. Price talk 09:56, 27 December 2009 (UTC)

It is true that stimulated emission can be described classically. Generally, second quantization is important for the description only at low photon fluxes. Since Einstein analyzed the exchange at the single photon level his presentation was necessarily quantum-mechanical. I inserted a reference to the classical theory and to Einstein's seminal work. Harry &#34;Snapper&#34; Organs (talk) 23:14, 29 February 2012 (UTC)


 * But Einstein also justs claims that the stimulated photon goes into the same mode (frequency, direction and polarisation). He doesn't do any QED stuff or anything (obviously). I was wondering about this behaviour of the process since I first heard of stimulated emission. I'd really like to see a "modern" explanation and calculation of stimulated emission. --93.203.203.162 (talk) 15:12, 6 July 2012 (UTC)

Only with electrons?
The introduction should be more general, stimulated emission works with any two-level system, for example the rotational and vibrational transitions that are used in gas lasers. —Preceding unsigned comment added by 192.167.204.14 (talk) 09:21, 26 November 2008 (UTC)

Different energies
What happens if the difference in the atom's ground state and excited state is smaller than the energy required to emit a photon identical to an incoming photon? —Preceding unsigned comment added by PAStheLoD (talk • contribs) 22:33, 9 July 2009 (UTC)


 * Probably there are non-radiative processes (mostly phonon absorption/emission) involved, too. This article needs expansion. --FDominec (talk) 18:49, 2 January 2010 (UTC)

Stimulated emission v.s. gain medium discussion
To me it semes this articles discusses more about optical gain than about stimulated emission. There should be a simple explanation to stimulated emission followed by a more detailed one. Now this is not how the article looks like. —Preceding unsigned comment added by 83.248.5.184 (talk) 08:26, 1 December 2009 (UTC)

Saturation Intensity
" The saturation intensity $$I_s$$ is defined as the input intensity at which the gain of the optical amplifier drops to exactly half of the small-signal gain. "

NO!!! This is the 3 dB compression point, which illustrates the output capabilites of an optical amplifier (see, for example, D. Derickson "Fiber optic test and measurement"). The saturation intensity is the light intensity, at which active medium becomes transparent (no gain, no loss) and the process of stimulated emission is as probable as absorption process. The populations of ground and excited states at saturation intensity become equal. --Ximeg (talk) 15:04, 7 July 2012 (UTC)
 * Sorry, I was not right --Ximeg (talk) 10:34, 11 July 2012 (UTC)

g-bar?
$$\bar{g}(\nu)$$ is used in multiple equations, but it isn't defined anywhere in the article. I would assume a relationship to the spectral line shape function $$g(\nu)$$, but at least to me the meaning of $$\bar{g}(\nu)$$ is not apparent from the context alone. Conquerist (talk) 00:36, 21 February 2013 (UTC)

Can't the first sentence say a photon is emitted?

 * In optics, stimulated emission is the process by which an atomic electron (or an excited molecular state) interacting with an electromagnetic wave of a certain frequency may drop to a lower energy level, transferring its energy to that field.

To what field? Can't this opening sentence state that a wave hits an electron, and a photon is emitted as the energy level of the electron drops? (I'd change it myself but as a layman I'm quite unsure.) Tarcil (talk) 22:44, 22 July 2013 (UTC)
 * I rewrote it in this direction (as a near layman). Hope it's clearer. 178.38.74.237 (talk) 20:57, 21 February 2015 (UTC)

Classical stimulated emission
Stimulated emission can also occur in classical models, without reference to photons or quantum-mechanics.

I adjusted the sentence to the above, referring to models, since no physical applications were given in the article. 129.132.211.139 (talk) 19:23, 21 February 2015 (UTC)

Spontaneous emission and ambient EM field
This blurb: "This is in contrast to spontaneous emission, which occurs at random intervals without regard to the ambient electromagnetic field." ...is misleading. Spontaneous emission most certainly does occur with regard to ambient EM field energy density, but it does not occur with regard to the mechanism by which stimulated emission takes place.

Can we please correct it? It's misleading some to conclude that photons are emitted willy-nilly without regard to the energy density gradient between the atom or molecule which would spontaneously emit, and the ambient EM field energy density. 71.135.45.180 (talk) 20:40, 26 June 2021 (UTC)


 * No, I think you're wrong inasmuch as the total rate of 2->1 transitions is considered (by definition) to be the rate of stimulated emission which IS proportional to the EM field (and the population in level 2) minus absorption (also proportional to the EM field and the population in level 1) plus spontaneous emission which ONLY depends on the population in level 2. So (assuming low temperature, no population inversion) while there is less NET emission from levels 2->1 when there is more energy in the EM field, that is accounted for as the SAME spontaneous emission but more absorption. But it's meaningless to talk about which photon was created or destroyed when by which process; that misunderstands the concept of photons and the sentence you quote has a slight problem in that regard I would say. Well, that's my understanding anyway.Interferometrist (talk) 01:17, 28 June 2021 (UTC)

Amplification of radiation in the stimulated emittion process
Detail information on this topic to understand the how radiation intensity increase and decrease so. 27.61.248.108 (talk) 04:27, 11 May 2022 (UTC)

Why the existence of stimulated emission refutes claims of surface warming by radiation from CO2, methane etc.
This is how the surface “knows” what to do with back radiation because such radiation always has photons with energy that matches one or more quantum energy gaps in the electrons that are orbiting in target atoms. This is because the Planck function for a cool source is always fully enveloped under the Planck function for the warmer (surface) target. This is how Nature ensures that every one-way passage of radiation obeys the Clausius ("hot to cold") corollary of the Second Law of Thermodynamics. The heat (ie the effective thermal energy transfer) via radiation from a hot source to a cooler target is a function of the area between the Planck functions of the source and target because this is the radiation for which there are no matching photons to cause stimulated emission. Instead these extra photons do cause heat into the target. This is in accord with the formula used by engineers to quantify such heat using the difference in the Stefan-Boltzmann calculations for source and target, such calculations being based on the integrals of those Planck functions. For more detail, read my 2012 peer-reviewed paper "Radiated Energy and the Second Law of Thermodynamics" which is on Researchgate, LinkedIn and at https://ssrn.com/author=2627605 - Douglas J. Cotton (Retired Physicist) — Preceding unsigned comment added by 2001:8003:26E2:3300:AC0B:C1E9:8BE2:3312 (talk) 01:10, 27 October 2022 (UTC)

Unexpected discussion of a transition state between two stationary states
The last paragraph of the Overview section, before History: "As the electron in the atom makes a transition between two stationary states (neither of which shows a dipole field), it enters a transition state which does have a dipole field, and which acts like a small electric dipole, and this dipole oscillates at a characteristic frequency. In response to the external electric field at this frequency, the probability of the electron entering this transition state is greatly increased. Thus, the rate of transitions between two stationary states is increased beyond that of spontaneous emission."

seems both under-defined+referenced (there is only one linked key word in the whole paragraph: "dipole"), and - to the degree that I undertand the paragrapg as written - largely irrelevant to the overview of stimulated emission. This text seems to be describing something like a Raman transition in between the two canonical stationary states, but clearly from the energy level diagram and all the rest of the text, such an intermediate state is not critical to the physics of the process.

I would suggest deleting the first 4 sentences of this 5-sentence paragraph, leaving only the final sentence, which does seem valid (and is completely independent of the first 4 sentences): "A transition from the higher to a lower energy state produces an additional photon with the same phase and direction as the incident photon; this is the process of stimulated emission." The reason I have not just deleted the sentences is I am open to hearing what they are supposed to be trying to convey, starting from a state of being quite baffled by them." — Preceding unsigned comment added by Crashbeard (talk • contribs) 22:48, 20 November 2022 (UTC)