Fifty years of nonlinear laser optics

The issue in your hands is devoted to the event widely celebrated by the international scientific community: the fiftieth anniversary of nonlinear laser optics, a branch of optics that includes "the study and application of phenomena related to a nonlinear response of matter to optical fields" [1]. It follows from the definition in Ref. [1] however that nonlinear optics originates from the pre-laser era. As early as 1926, working at the Department of Physics, M. V. Lomonosov Moscow State University, S. I. Vavilov and V. L. Levshin detected light absorption saturation in uranium glasses. Later, weak luminescence depolarisation nonlinearity and photoinduced absorption dichroism were discovered. Those studies had a pioneering character, but they were initiated in the years when physics had very modest experimental facilities. Vavilov's important role in the advent and subsequent development of nonlinear optics was repeatedly emphasised by Academician Khokhlov [2]: "It is well known that S. I. Vavilov was the father of nonlinear optics. His work in this area was begun long before the advent of lasers. The first nonlinear effect — light absorption saturation in uranium glasses — was discovered by Vavilov and Levshin in 1926". Moreover, the term "nonlinear optics" was coined by Vavilov.