Abstract
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.
Highlights
Fulfilling the PM condition causes generated wave-amplitude contributions from different locations of the material to sum up in the phase domain
The μ-PD was invented for the growth of single crystal fibers[22,23]; it has been used for the growth/solidification of eutectic-based, photonic crystal-like materials[24,25], metamaterials[26] and bulk nanoplasmonic materials obtained by direct doping of glass matrices with plasmonic nanoparticles[27]
We reveal that ZnWO4 single-crystal has the ability to modulate the frequency of a pump wave via second-harmonic generation
Summary
Pawel Osewski[1], Alessandro Belardini[2], Emilija Petronijevic[2], Marco Centini[2], Grigore Leahu[2], Ryszard Diduszko[1], Dorota A. Crystalline materials lacking inversion symmetry can exhibit second-order nonlinear optical properties, which can give rise to the phenomenon of frequency doubling[1], where an input (pump) wave generates a wave with twice the optical frequency in the medium. We demonstrate phase-matched second-harmonic generation and white-light generation at normal incidence in a biaxial monoclinic ZnWO4 single crystal grown by the micro-pulling-down method. To our knowledge, this is the first demonstration of efficient SHG in zinc tungstate. We report on the possibility of further improving SHG efficiency by crystal annealing
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