Single Crystal BBO Microwires And Nanowires:Synthesis And Optical Properties

As one-dimensional (ID) building blocks for micro-/nanoscale photonic circuits and devices, microwires and nanowires (MNWs) have attracted considerable attention in optics and photonics applications due to their applications ranging from optical modulation, wavelength conversion to near-field imaging. Present researches on1D free-standing MNWs mainly focus on the micro-/nanofibers, semiconductor and metal nanowires. Meanwhile, preparation and characterization of new nonlinear1D micro-/nanomaterials are also under exploration which will become one of the focus of attention.As one of the most widely used nonlinear optical crystals, β-BaB2O4(BBO) crystals offer special advantages of high nonlinear optical coefficients and high damage threshold. However, so far optical-quality BBO MNWs have not been reported.Based on previous research on BBO micro-/nanostructures, we have successfully synthesized BBO MNWs with sol-gel and hydrothermal methods, and investigated their optical properties in details.In the first part of this work (Chapter2), we report the synthesis of BBO MNWs using an organic-free hydrothermal method assisted with post annealing, with BaCl2·6H2O, NaOH and H3BO3as source materials. The influence of the reactants concentration, reaction time, reaction temperature and substrates at the heat treatment were studied. XRD、SEM and HRTEM were used to examine the as-synthesized BBO MNWs. The MNWs show triangular cross-section, with diameters ranging from500nm to2μm and lengths up to several hundred micrometers and, with excellent diameter uniformity and surface quality.We investigate optical waveguide properties of BBO MNWs. Our result show that BBO MNWs have waveguide capabilities with propagation losses of0.30dB/μm (at532nm) and0.21dB/μm (at671nm), respectively. In the third part of this work (Chapter4), we study the SHG in BBO MNWs. When excited by waveguided1064nm picosecond laser pulses, evident SHG signal at532nm is observed. The conversion efficiency of SHG is measured to be about8.4%, which is higher compared to bulk crystal.Our results show that, optical-quality BBO MNWs can be synthesized using sol-gel and hydrothermal methods. Under waveguiding excitation, BBO MNWs can be used as nonlinear optical waveguides with high SHG efficiency. With further efforts to improve the synthesis condition and quality, these BBO MNWs may play important roles in future micro-/nanoscale nonlinear optical applications.