Saturation effects in nonlinear absorption, refraction, and frequency conversion: a review

Over the past few decades, there has been extensive research work carried out in the area of nonlinear optics and opened a myriad of applications in material science and engineering. In coherent light-matter interaction, the nonlinear optical processes exhibit a saturation behavior at high-intensity laser excitation. This review article was written based on most of the research articles published till now in such a way to provide complete information on saturation effects, generally seen in nonlinear optics. In this review article, we have given a brief discussion on the saturation effect which is taken place in nonlinear absorption, refraction, and frequency conversion. The saturation in single- and multi-photon absorption processes is discussed in detail. We have also given a detailed analysis of the saturation that occurred in the nonlinear refractive index and how the nonlinear gradient refractive index creates diffraction in the transmitted laser beam. Further, we discussed on the saturation involved in the nonlinear frequency conversion due to various factors. Our review will be of interest to the large community that seeks to use the applications of high-intensity light-matter interaction.