A Brief Survey of Nonlinear Optics: Second Harmonic Generation and Two-Photon Absorption

Abstract

The purpose of this chapter is to introduce the theoretical fundamentals responsible for nonlinear optical (NLO) processes. Fascinating key processes such as second harmonic generation (SHG), third harmonic generation (THG), and two-photon absorption (TPA) are the consequences of light–matter interaction described by higher order corrections. The use of these techniques is the most popular for multiphoton imaging which is a powerful microscopy technique that has found growing application in fields ranging from fundamental physics to biomedicine.