Talk:Sum-frequency generation

Mechanism
Are there special conditions which are necessary for photon combination to happen, or can any two photons do so? Do they have to collide with a particular material? What kind of proximity in time and space is needed? -- Beland (talk) 03:00, 12 March 2010 (UTC)

Assessment comment
Substituted at 07:17, 30 April 2016 (UTC)