Self-Phase-Matched Second-Harmonic and White-Light Generation in a Biaxial Zinc Tungstate Single Crystal

Second-order nonlinear optical materials are used to generate new frequencies by exploiting second-harmonic generation (SHG), a phenomenon where a nonlinear material generates light at double the optical frequency of the input beam. Maximum SHG is achieved when the pump and the generated waves are in phase, for example through birefringence in uniaxial crystals. However, applying these materials usually requires a complicated cutting procedure to yield a crystal with a particular orientation. Here we demonstrate the first example of phase matching under the normal incidence of SHG in a biaxial monoclinic single crystal of zinc tungstate. The crystal was grown by the micro-pulling-down method with the (102) plane perpendicular to the growth direction. Additionally, at the same time white light was generated as a result of stimulated Raman scattering and multiphoton luminescence induced by higher-order effects such as three-photon luminescence enhanced by cascaded third-harmonic generation. The annealed crystal offers SHG intensities approximately four times larger than the as grown one; optimized growth and annealing conditions may lead to much higher SHG intensities

Bulk nanocomposite made of ZnO lamellae embedded in the ZnWO4 matrix: growth from the melt

International audienceAbstract Zinc oxide (ZnO) nanostructures exhibiting high exciton binding energy and efficient radiative recombination, even at the room temperature, are of increasing interest due to their prospective exploitation in optoelectronic and laser applications. However, attempts to synthesize well-ordered structures through simple and fast process have faced many difficulties. Here, we demonstrate a novel manufacturing method of ZnO lamellae embedded in a crystalline wide band gap dielectric matrix of the zinc tungstate, ZnWO 4 . The manufacturing method is based on a directional solidification of a eutectic composite, directly from the melt, resulting in a nanostructured bulk material. Electron microscopy studies revealed clear phase separation between the ZnO and ZnWO 4 phases, and cathodoluminescence confirmed exciton emission at room temperature and thus high quality and crystallinity of the ZnO lamellae, without defect emission. Hence, utilization of directional solidification of eutectics may enable cost-efficient manufacturing of bulk nanostructured ZnO composites and their use in optical devices. Graphical abstrac