Talk:Second-harmonic generation

External link request
I have substantially revised the article and suggest that someone adds the following external link (to a page under my control):

http://www.rp-photonics.com/frequency_doubling.html Encyclopedia of laser physics and technology on frequency doubling = second harmonic generation

RPaschotta 13:30, 30 Apr 2006 (UTC)
 * Done. Thanks very much for the revisions, and for not inserting a link to your own site. Your site is excellent and much-used by myself and colleagues, by the way.--Srleffler 22:37, 4 November 2006 (UTC)

Efficiency
Can we have some numbers about maximum real world conversion efficiency? Depending on pulse energy, length, wavelength, rep. rate? I've heard, that flat top ns pulses allow 0.9, while gaus fs only 0.2. Arnero 11:15, 12 July 2007 (UTC)


 * This is very parameter dependant. If you talk about conversion of a weak signal through a strong pump, you can get close to unity. If you talk about the conversion of all input photons, you are typically limited by the triple harmonic generation which will take some of your signal away. The numbers you have heard of are likely to be valid for a given crystal with fixed experimental parameters only. UnHoly 06:18, 13 July 2007 (UTC)

Can the output-complemend be regenerated over .2? Any lasers do this? -lysdexia 14:12, 21 October 2007 (UTC) —Preceding unsigned comment added by 68.123.4.253 (talk)

Article importance
I added "Mid" to the article's importance in the Physics Project. I did so because Optics is Top-Class, and the hierarchy should be Optics->Nonlinear Optics->Second Harmonic Generation. However, WP:1.0/Criteria states that Mid means that "Subject fills in more minor details". Since I work in this field I'm inclined to think this article should be rated "High" importance, but I didn't want to overrate it. --Arnoques (talk) 20:10, 27 November 2008 (UTC)


 * I'd say that "mid" is right - within the Physics project, there's a guideline of "High: Important or famous. Something an undergraduate physics major could have heard of or studied." I'd argue that SHG is a more specialist topic than that.  I've also updated the class to "C" - does this seem right? Djr32 (talk) 13:04, 30 November 2008 (UTC)


 * I agree with both assesments. --Arnoques (talk) 02:30, 1 December 2008 (UTC)

Mechanism
Are there special conditions which are necessary for photon combination to happen, or do any photons of the same frequency capable of combining? Do they have to collide with a particular material? What kind of proximity in time and space is needed? -- Beland (talk) 02:55, 12 March 2010 (UTC)

Hyperpolarizability
It is time for a physical chemist to explain this effect in terms of molecular hyperpolarizability, the second-order electric susceptibility per unit volume. In the last fifteen years, chemists have been synthesizing molecular substances with hyperpolarizabilities 4-5 orders of magnitude greater than those of ionic substances. How about Hyper Rayleigh Scattering? You can get SHG out of that too. Laburke (talk) 22:56, 10 September 2011 (UTC)

Index matching
I worked on second harmonics generation as a physics student many years ago. I recall that index matching (in a birefringing crystal) was essential for effective SHG. Is this still required? I guess it is fairly simple to explain, without formulae: without index matching, the generated 2nd harmonic wavelets extinguish each other. Rbakels (talk) 21:48, 18 November 2011 (UTC)

Definition of Variables in Derivation
A non-expert (like myself) may not know what some of the symbols mean. For people familiar with optics variables such as the index of refraction are obvious, but I don't know what d_eff means. Could someone clarify this in the article? Thanks, Mallonna (talk) 04:42, 27 April 2013 (UTC)

Resonant interaction and Draft:three-wave equation
There is now an article on resonant interaction and I believe that it provides the correct theoretical background for this article. More precisely, Draft:three-wave equation does this too, since assorted non-linear optics papers mention this equation or something similar... I don't want to modify this article because I don't know the details. 67.198.37.16 (talk) 01:48, 17 September 2020 (UTC)

Is SHG available in the x-ray / gamma photon spectrum for medical applications?
Is SHG a.k.a frequency-doubling only available for IR/visible/UV light spectrum or X-ray and gamma photons as well? This question is of great practical importance but not clearly spelt out in the article.

E.g. Cobalt-60 machine is an affordable and low-maintenance (replace isotope capsule once in 5 years) "passive mode" radiation therapy device. It's now considered obsolete for having only 1.25 MeV gamma-ray output, reaching just a few cm under the skin. Modern electron LINACs provide 6 MeV or more in tungsten-target gamma mode, reaching tumors deeper inside the body, but are more expensive and maintenance-intensive, not well-suited for the developing world. If Cobalt machines could be fitted with two stages of SHG, they could output 1.25*2*2 = 5 MeV gamma and enable better cancer rad treatment in poor / remote locations. Efficiency loss could be compensated by making the Co60 capsule larger and its lead shielding "egg" thicker walled. 78.131.76.35 (talk) 09:46, 5 July 2023 (UTC)