Nonlinear optics

Abstract

This chapter provides a brief introduction into the basic nonlinear-optical phenomena and nonlinear optics discusses some of the most significant recent advances and breakthroughs in nonlinear optics, as well as novel applications of nonlinear-optical processes and devices. Nonlinear optics is the area of optics that studies the interaction of light with matter in the regime where the response of the material system to the applied electromagnetic field is nonlinear in the amplitude of this field. At low light intensities, typical of non-laser sources, the properties of materials remain independent of the intensity of illumination. The superposition principle holds true in this regime, and light waves can pass through materials or be reflected from boundaries and interfaces without interacting with each other. Laser sources, on the other hand, can provide sufficiently high light intensities to modify the optical properties of materials. Light waves can then interact with each other, exchanging momentum and energy, and the superposition principle is no longer valid. This interaction of light waves can result in the generation of optical fields at new frequencies, including optical harmonics of incident radiation or sum- or difference-frequency signals. It can even lead to the production of ultrashort light pulses in the attosecond (10⁻¹⁸ s) domain. The experimental setup needed to obtain high-order harmonics is given followed by a discussion of the microscopic and macroscopic physics underlying the generation of attosecond pulse trains and single attosecond pulses. The field of attosecond science is reviewed, different measurement techniques are described, and some applications are discussed.