“…This dependence leads to various particular nonlinear laws for the permittivity: cubic (Kerr), quintic, cubic-quintic, polynomial nonlinearities, power nonlinearity with noninteger degree, saturated nonlinearities, and so on. These nonlinearities were actively experimentally [4,5,[38][39][40][41][42][43][44][45][46] as well as theoretically [2,6,9,13,21,32,[35][36][37][47][48][49][50][51][52][53][54][55][56] studied.…”