Optical materials for short wavelength generation

This review reports on recent achievements in the synthesis and crystal growth of materials for efficient generation of short wavelength light. Materials exhibiting harmonic generation, stimulated Raman scattering or upconversion are discussed. Early and recent work has confirmed that ferroelectric oxide and berate crystal are most feasible for harmonic generation, while structures containing molecular-like entities seem to be able to generate multiple stimulated Raman scattering responses. In the field of upconversion, halide materials turned out to be more efficient than e.g. oxides. Low-phonon materials such as chlorides or bromides yielded efficient luminescences down to the near UV region. However, chloride and bromide crystals containing rare earth ions generally are not stable in air. The search for stable host crystals may be considered a major challenge in the synthesis of new materials for upconversion. Independent of the nonlinear optical mechanisms of short wavelength generation, formation of waveguides gained considerable importance, because production for real world applications most evidently will follow a waver type technology. (C) 1999 Elsevier Science S.A. All rights reserved.