Editing Nonlinear optics (section)

===Frequency-mixing processes===
* [[Second-harmonic generation]] (SHG), or ''frequency doubling'', generation of light with a doubled frequency (half the wavelength), two photons are destroyed, creating a single photon at two times the frequency.
* [[Third-harmonic generation]] (THG), generation of light with a tripled frequency (one-third the wavelength), three photons are destroyed, creating a single photon at three times the frequency.
* [[High-harmonic generation]] (HHG), generation of light with frequencies much greater than the original (typically 100 to 1000 times greater).
* [[Sum-frequency generation]] (SFG), generation of light with a frequency that is the sum of two other frequencies (SHG is a special case of this).
* [[Difference-frequency generation]] (DFG), generation of light with a frequency that is the difference between two other frequencies.
* [[Optical parametric amplification]] (OPA), amplification of a signal input in the presence of a higher-frequency pump wave, at the same time generating an ''idler'' wave (can be considered as DFG).
* [[Optical parametric oscillation]] (OPO), generation of a signal and idler wave using a parametric amplifier in a resonator (with no signal input).
* [[Optical parametric generation]] (OPG), like parametric oscillation but without a resonator, using a very high gain instead.
* [[Half-harmonic generation]], the special case of OPO or OPG when the signal and idler degenerate in one single frequency, 
* [[Spontaneous parametric down-conversion]] (SPDC), the amplification of the vacuum fluctuations in the low-gain regime.
* [[Optical rectification]] (OR), generation of quasi-static electric fields.
* [[Nonlinear light-matter interaction with free electrons and plasmas]].<ref>{{cite journal|title=Experimental observation of relativistic nonlinear Thomson scattering|first1=Szu-yuan|last1=Chen|first2=Anatoly|last2=Maksimchuk|first3=Donald|last3=Umstadter|date=17 December 1998|journal=Nature|volume=396|issue=6712|pages=653–655|doi=10.1038/25303|arxiv=physics/9810036|bibcode=1998Natur.396..653C|s2cid=16080209}}</ref><ref>{{cite journal|title=Observation of Nonlinear Effects in Compton Scattering|first1=C.|last1=Bula|first2=K. T.|last2=McDonald|first3=E. J.|last3=Prebys|first4=C.|last4=Bamber|first5=S.|last5=Boege|first6=T.|last6=Kotseroglou|first7=A. C.|last7=Melissinos|first8=D. D.|last8=Meyerhofer|first9=W.|last9=Ragg|first10=D. L.|last10=Burke|first11=R. C.|last11=Field|first12=G.|last12=Horton-Smith|first13=A. C.|last13=Odian|first14=J. E.|last14=Spencer|first15=D.|last15=Walz|first16=S. C.|last16=Berridge|first17=W. M.|last17=Bugg|first18=K.|last18=Shmakov|first19=A. W.|last19=Weidemann|date=22 April 1996|journal=Phys. Rev. Lett.|volume=76|issue=17|pages=3116–3119|doi=10.1103/PhysRevLett.76.3116|pmid=10060879|bibcode=1996PhRvL..76.3116B|url=https://cds.cern.ch/record/311275|type=Submitted manuscript|access-date=6 September 2018|archive-url=https://web.archive.org/web/20190621224531/https://cds.cern.ch/record/311275|archive-date=21 June 2019|url-status=dead}}</ref><ref>{{cite journal |last1=Koga |first1=J. |last2=Esirkepov |first2=T.Z. |last3=Bulanov |first3=S.V. |title=Nonlinear Thomson scattering in the strong radiation damping regime |journal=Physics of Plasmas |volume=12 |issue=9 |pages= |date= 2005|doi=10.1063/1.2013067 }}</ref><ref>{{cite journal|title=Plasma mirrors for ultrahigh-intensity optics|first1=C.|last1=Thaury|first2=F.|last2=Quéré|first3=J.-P.|last3=Geindre|first4=A.|last4=Levy|first5=T.|last5=Ceccotti|first6=P.|last6=Monot|first7=M.|last7=Bougeard|first8=F.|last8=Réau|first9=P.|last9=d’Oliveira|first10=P.|last10=Audebert|first11=R.|last11=Marjoribanks|first12=Ph|last12=Martin|date=1 June 2007|journal=Nat Phys|volume=3|issue=6|pages=424–429|doi=10.1038/nphys595|bibcode=2007NatPh...3..424T}}</ref>