|WikiProject Physics||(Rated B-class, Mid-importance)|
"When light is scattered from an atom or molecule, most photons are elastically scattered (Rayleigh scattering). The scattered photons [...]" -- I think, someone should rewrite these lines, they sound scattering to me =)
How do I tell if for example http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/raman.html is copyright? Should I incorporate parts of that text (rewriting them a bit differently) into this one to make it more complete?
- The simple answer is that it is almost certainly copyright, (probably of the university rather than the author in this case) so you can't incorporate parts of the text by copy and paste. What you can do is use it as a reference of the facts, and can then write text based on those facts. Average Earthman 13:05, 7 Oct 2004 (UTC)
That seems pretty clear, thanks. I'll do that when I get the time to do a decent job of it unless someone else can do it before. Also I think attention will have to be paid to not overlap too much with information already present on Raman spectroscopy...
- The second paragraph needs rewriting. Perhaps this revision makes sense:
- The interaction of light with matter in a linear regime allows the matter to absorb or stimultaneously emit light, the energy of which precisely matches the difference in energy levels of an interacting electron.
- Italic parts were changed. I'm not sure if this revision is accurate, but the original makes little sense. --Weevil 10:15, 6 Apr 2005 (UTC)
2nd or 3rd order?
Is Raman scattering a 2nd or 3rd order effect? It says here it's 2nd order, but I was under the impression it was 3rd order. (If it can happen in symmetric materials, then it must be 3rd order.)
Raman scattering unless it is stimulated is a linear optical effect!
- Raman scattering is a third order effect. It occurs in nonisotropic and isotropic medium.
- see for instance "Quantum Electronics" by Amnon Yariv
Most Raman is first order, the Raman scattering increases lineraly with the excitation intensity! You need second order pertubation theory to describe within quantum mechanics and there are two photons and one lattice (or molecular) vibration involved, but it is still first order. However, when you try really hard you can get second and third order Raman signals and coherent anti-stokes Raman scattering (CARS) is third order. Grmf
Then i delete the statement about Raman beeing third order, see e.g. D. A. Long, Raman Spectroscopy (McGraw-Hill, 1977). There is lots which could be improved in the article Grmf
Raman scattering is a third order effect. See page 261 of Principles of Nonlinear Optical Spectroscopy by Shaul Mukamel 1995. Any statement refering to it as a first order effect is either wrong, or a limited classical description. Since the output frequency differs from the input frequency, it cannot be first order. Secondly, it happens in symmetric materials, and is therefore not second order. Writting a Feynman diagram, or using a wave mixing energy level (WMEL) diagram shows that it is a third order effect. The statement that "most raman is first order" makes no sense in a quantum mechanical frame. CARS, stimulated Raman, and your normal Raman scattering experiment differ in how many excitation lasers versus vacuum photons are used (ignoring phase matching, naturally). While looking at how the signal scales with respect to an input laser can be used as an fair guide to determine the order of an effect classically, one cannot ignore vacuum photons for a rigorous treatment. Nmathew 18:02, 18 April 2007 (UTC)
Hm, this seems to be a difference in viewpoints of a theoretician and experimentalist. For me (the experimentalist), a limited classical description is perfectly fine as long as it describes the experiment well. The classical treatment describes normal Raman scattering (spontaneous, not too high electric field) well as long as it is off resonance. In this sense it is right to say that Raman is a linear process. The non-linearity needed to get a frequency change is provided by the interaction with the lattice- (or molecular-) vibration (or rotation). There is a methodological aspect as well, as Shaul Mukamel writes in the introduction of his book “Principles of Nonlinear Optical Spectroscopy”: Optical measurements can be naturally classified according to their power-law dependences on the external electric field. No virtual photons here! That is why he writes on page 261: … “ in a strict sense the technique is ‘linear’.”, with “the technique” referring to spontaneous light scattering Raman and fluorescence). You might have gained further insight into the process by going through the full quantum mechanical treatment, but I guess you have not learnt anything more than the experimentalists has already found out. And it is far too complicated for an encyclopedia article anyhow. Grmf
Uses of Raman Effect
It should be mentioned the DTS (Distributed Temperature Sensing) in which the Stokes and the anti-Stokes Raman scattering are compared in a SRS system (only one of them is temperature-dependent, I can't remember which). This is used for measuring temperature along electrical cables and oil wells, early fire detection as well as many other applications.
Another new use for stimulated raman scattering is in-vivo video microscopy. This just a news article: http://www.eurekalert.org/pub_releases/2010-12/hu-nmt120110.php, the original journal article's citation is "Science 3 December 2010: Vol. 330 no. 6009 pp. 1368-1370 DOI: 10.1126/science.1197236 " (I'm relatively new to authoring so I'm unsure how to proceed) Falconerd (talk) 02:45, 7 December 2010 (UTC)
It sounds like this effect can have a directional bias (light is not scattered in all directions equally, without regard to the direction of the incoming radiation). It would be interesting to get details on that and also have a diagram illustrating it.
The Raman effect has indeed a directional bias: the intensity of Raman scattering depends on the scattering angle (and as a matter of fact, the polarization state of the scattered light also depends on the scattering angle). However, unlike for Rayleigh scattering, no simple formula can be found that describes this dependence in all situations. The precise form of the dependence varies with kind of transition that is taking place and with the polarization states. However, I don't know what is appropriate to add to the Wikipedia article for this point. More information can be found in following reference: "The Raman Effect, A Unified Treatment of the Theory of Raman Scattering by Molecules" by Derek A. Long (ISBN 9780471490289, DOI 10.1002/0470845767). 188.8.131.52 (talk) 11:42, 2 April 2013 (UTC)
Maybe it should be deleted: http://www.onforum.com/tutorials/acrobat/raman.pdf does not work, it does not send you to a Raman Scattering Pdf. —Preceding unsigned comment added by 184.108.40.206 (talk) 13:45, 13 November 2007 (UTC)
"In 1922, Indian physicist C. V. Raman published his work..." - is it necessary to emphesise that he was Indian? This never done for British, German, American physicists, etc., and it's inconsistent with, for example, Thomson scattering ("... first explained by the physicist J.J. Thomson"). The emphasis on his nationality seems to imply that prominent Indian physicists are uncommon, which is arguably not the case.
I'm not Indian by the way, so this isn't a Nationalistic chip-on-the-shoulder. I just like consistency :D
C. V. Raman was the first Indian scientist to win the Nobel Prize for Physics, and hence it makes sense to emphasise his nationality in this sense as it is a (arguably) somewhat significant historic fact. - Shaktal
Update External Link
I am the program coordinator of the ACS-National Historic Chemical Landmarks program. I have updated the references to ACS-NHCL web content, as those pages are being replaced. KLindblom (talk) 21:50, 6 June 2012 (UTC)