Third-Order Nonlinearities
المؤلف:
Walter Koechner Michael Bass
المصدر:
Solid-state Lasers
الجزء والصفحة:
343
23-1-2021
1663
Third-Order Nonlinearities
Third-order optical nonlinearities involve the nonlinear susceptibility tensor χ(3). This term governs third harmonic generation, optical Kerr effect, Raman effect, and Brillouin scattering. In general, χ(3) will couple together four frequency components, that is, three fields interact to produce a fourth field,
.......(10.7)
where ω4 = ω3 + ω2 + ω1. χ(3) is a four-rank tensor with 81 elements, because an array of 3×27 coefficients couple a single component of the polarization P to three independent components of three electric field vectors.
The third-order optical nonlinearity is thus a four-photon process. There can be up to three different input laser frequencies, but several of the frequencies can also be the same. In a lossless medium the susceptibility coefficients of χ(3) are real. In this case, the primary nonlinear optical effects are the generation of new frequency components and the intensity-dependent change in the refractive index (Kerr effect). In third-order interactions involving absorption, the imaginary part of χ(3) describes Raman and Brillouin scattering.
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