Novel nonlinear crystals

Abstract

The field of nonlinear optics, as we know it today, was born as a direct consequence of the invention of the laser in the early sixties. Nonlinear effects in electromagnetism had been observed as early as the late nineteenth century by Kerr, Rontgen, Kundt, and Pockels, and later by Raman in 1927 when he discovered spontaneous scattering of light into new wavelengths in passing through a transparent medium. However, it was not until 1961 that the first observation of coherent nonlinear optical effects was made by Franken et al. (1961), who demonstrated second-harmonic generation of light in the crystal of quartz. This discovery propelled the field of modern nonlinear optics and initiated intensive research in materials science and crystal technology. In a short period following this discovery, several other nonlinear optical phenomena including parametric amplification and frequency mixing were identified, and many important concepts such as phase-matching were quickly developed. During this period, much effort was also expended at the fundamental level on studies of crystal optics and the understanding of the most important aspects of nonlinear interactions of light with matter. With the rapid parallel progress in laser technology and the availability of higher-intensity laser sources in new spectral regions, an increasing number of nonlinear optical experiments became viable and many new nonlinear optical techniques were developed. Today, nonlinear optics is a vast area, and undoubtedly one of the most important areas, of physics, with a diverse range of applications in many other areas of science. The aim of this chapter is to provide an insight into this subject and review some of the most recent progress made in the development of new nonlinear optical materials and devices. The early part of the chapter is concerned with a brief discussion on the physical origin of some of the important nonlinear optical effects and techniques used for the exploitation of these effects, such as phase-matching. This section will also contain a review of crystal optics and a discussion of nonlinear susceptibilities. In the later part, we describe several important nonlinear materials that have recently been developed, discuss their use in frequency-conversion devices, and outline their potential for future nonlinear optical applications.