Nonlinear optics

Lore & Background

That year saw the almost simultaneous observation of two-photon absorption at Bell Labs and the discovery of second-harmonic generation by Peter Franken et al. at University of Michigan, both shortly after the construction of the first laser by Theodore Maiman. However, some nonlinear effects were discovered before the development of the laser. The theoretical basis for many nonlinear processes was first described in Bloembergen's monograph 'Nonlinear Optics'.

Reader's Guide

Nonlinear optics is significant because it explains how intense light can alter the optical properties of materials, leading to a host of phenomena such as frequency doubling, high-harmonic generation, and self-focusing. Its legacy includes enabling technologies like laser mode-locking, optical parametric oscillators, and attosecond pulse generation. The field is divided into perturbative nonlinear optics, valid below 10¹⁴ W/cm², and nonperturbational or extreme nonlinear optics, which investigates extremely high-order harmonics and relativistic effects. Nonlinear optics also underpins practical devices such as electro-optic modulators and acousto-optic modulators, and its study continues to advance understanding of light-matter interactions at the most fundamental levels.

Did You Know?

• Maxwell's equations are linear in vacuum, so nonlinear processes only occur in media, though quantum electrodynamics predicts vacuum nonlinearity above the Schwinger limit.
• The motion of bound electrons has a very short response timescale, making it particularly relevant for ultrafast nonlinear optics.