Talk:Two-photon absorption

message: How does this compare to "Two-photon excitation"?  Should that term be linked back to here?  Should a redirect of that come here?  Should this be renamed to that?  Or am I just missing it?  -RJFerret 05:15, 12 July 2006 (UTC)

message: I'm also saying that this is a really poor article.  It tries to reason (incorrectly) why the 2 photon absorption process "should" be called 3 photon absorption.  This is totally incorrect and that's just the beginning.  
I just made some edits in the article, but I'm pretty unsatisfied. It's a bit of a dog's dinner and could do with a rewrite all over. Yeah, I know, I'm whining when what I should really do is get down and do it myself...
In particular the "Measurements" part, which was much needed, could now do with some expansion (I also personally don't like the use of "β" for cross-section, but that's a whole other discussion).
I'll make an effort to come back and do something when I can find time...
          * I hope I may write here something..
            very nice, that you inserted the 'Measurements' part.. but where from do you have
            that formula? What about References?? I'm afraid I shouldn't have Wikipedia in my
            References in my Bachelor-Thesis.. but I need this formula and can't find it nowhere
            else   
            Lg
            Alex, 31.08.2010 —Preceding unsigned comment added by 141.84.219.200 (talk) 12:44, 31 August 2010 (UTC)
replies: text:  Well, (almost a year later!) I've done that for you. • TheBendster (talk) 28 April 2008, 07:34 (UTC)
Hi, I believe the reference to the first experimental verification is incorrect. I've recently been studying this topic and came across a review paper of the subject, Cagnac, B., 1994, Laser Physics, Vol. 4, No. 2, that references Hughes, V.W. and Grabner, L., 1950,Phys. Rev., 79, 314, 819 as the first experimental observation of the two photon absorption phenomenon. Refer to section V. of the Hughes and Grabner paper. - user Generalphas  —Preceding unsigned comment added by Generalphas (talk • contribs) 19:29, 21 May 2010 (UTC)
thread_title:  This needs work. 

message: I think the discussion of selection rules is misleading as written:
"The selection rules for TPA are therefore different than for one-photon absorption (OPA), which is dependent on the first-order susceptibility. For example, in a centrosymmetric molecule, one- and two-photon allowed transitions are mutually exclusive. In quantum mechanical terms, this difference results from the need to conserve spin. Since photons have spin of ±1, one-photon absorption requires excitation to involve an electron changing its molecular orbital to one with a spin different by ±1. Two-photon absorption requires a change of +2, 0, or −2."
Only circularly polarized light carries angular momentum. Linearly polarized light does not, but there are still different selection rules for one- and two-photon absorption. These selection rules have to do with the symmetry of the states under inversion (or parity). The spin of the states is the same for both processes.
Perhaps the article could be amended so that the example refers explicitly to circularly polarized light, or generalized to include other examples of one- and two-photon processes that probe states with different symmetries.
Jmkinder1 (talk) 20:34, 3 June 2008 (UTC)
replies: text: All photons carry one unit of spin, regardless of polarization. -- Fuzzyeric (talk) 15:17, 3 November 2009 (UTC)
thread_title:  Selection Rules 

message: Hi, I am a little confused with the formula for the two-photon absorption coefficient \beta, because when I insert the magnitudes N and \sigma in units with cm how can then \beta have the unit of m/W? A formula for \beta is published in Kato et. al. Chem. Eur. J. 2006, 12, 2303-2317, unfortunately the units of \beta are not mentioned. However it seems as if in that paper \beta is cm/W because all length are given in cm in that paper. The rest of the formula is equal to that given here on Wikipedia.
Could some expert comment on that!  — Preceding unsigned comment added by 140.78.174.177 (talk) 08:43, 10 September 2012 (UTC)
thread_title:  TPA Coefficients