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From Wikipedia, the free encyclopedia
Nonlinear optics (NLO) is the branch of optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light.
Nonlinear effects in physics have been observed and described in multiple fields, however it is only comparatively recently that the nonlinear effects in optics have been of practical interest. Optical nonlinearities in materials are typically only significant for very large light intensities, where the magnitude of the electric field is comparable to that of the binding fields of the atoms of the material, with such intensities typically only accessible using a laser. As such the field has grown immensely with the invention and continued development of high power laser systems. In this intenisty regieme, the optical properties of the material, such as the refractive index, can be modified by the incident light, and the superposition principle no longer holds, leading to the modification of properies such as the frequency of the incident light. At extremely high optical intenisties above the Schwinger limit, the vacuum itself is expected to become nonlinear.
The nonlinear response of the material yields a large number of optical phenomenon. Many of these effects have practical applications in the modern laser system construction, and can be used in a number of experimental applications including spectroscopy