ABSTRACT
Nonlinear optics is the study of the interaction between intense electromagnetic radiation and matter. It describes phenomena arising when the response of a medium to the electric field of light leaves the linear regime associated with the familiar and ubiquitous effects, such as reflection, refraction and absorption, comprising classical optics. In the presence of a sufficiently intense light source, the approximation of linearity breaks down. A new and much broader class of optical phenomena may be observed. Prototypical among these nonlinear optical effects is the production of light at new frequencies. Indeed, nonlinear optics is generally considered to have begun in 1961 when Franken and coworkers demonstrated optical secondharmonic generation (SHG) by insertion of a quartz crystal along the path of a laser beam [1]. In addition to the generation of new frequencies from excitation of a monochromatic source, nonlinear optical effects lead to the coupling between beams of identical and disparate frequencies, as well as to the action of a beam of light on itself.
