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 Spontaneous parametric down-conversion (SPDC), the amplification of the vacuum fluctuations in the low gain regime Optical Kerr effect, intensity dependent refractive index Self-focusing Kerr-lens modelocking (KLM) Self-phase modulation (SPM), a effect Optical solitons Cross-phase modulation (XPM) Four-wave mixing (FWM), can also arise from other nonlinearities Cross-polarized wave generation (XPW), a effect in which a wave with polarization vector perpendicular to the input is generated Sample non-parametric nonlinear processes: Stimulated Raman scattering Raman amplification Two-photon absorption, simultaneous absorption of two photons, transferring the energy to a single electron Multiphoton absorption Multiple photoionisation, near-simultaneous removal of many bound electrons by one photon See also Nonlinear optics Notes References Nonlinear optics Quantum optics