New oxyborate crystal, GdCa₄O(BO₃)₃: Defects and optical properties

Large size and high quality doped and undoped GdCOB crystals were grown using Czochralski pulling method from Pt crucible under air atmosphere. The defects were observed using microscopy combined with chemical etching method. The cause of the twins, inclusions and dislocation defects in GdCOB crystal were discussed. The optimum phase-matching direction is out of the main plane, which is along (θ = 66.8, φ = 132.6). The intracavity second-harmonic-generation (SHG) conversion efficiency of 12 mm long GdCOB cut along this optimum PM direction is 25%, 1.22 W continuous-wavelength green laser was obtained at 10 W LD power. When GdCOB crystal is doped by Sr²⁺, Bi³⁺ Li⁺, Yb³⁺ and Tm³⁺ cations, the SHG conversion efficiencies are improved obviously because the cations make the anion groups in GdCOB crystal more distorted. Gd_0.37Y_0.63COB crystal can realize non-critical PM third-harmonic-generation (THG) at room temperature. The THG properties of β-BBO and Gd_0.37Y_0.63COB crystals are compared. The self-frequency-doubling (SFD) properties of NdGdCOB crystal were studied. The SFD optical-optical conversion efficiency of NdGdCOB crystal is 14.4% when pumped by Ti:sapphire laser while it is 7.7% when pumped by dye-laser. The passive Q-switched and modulated Q-switched phenomena were analyzed. The power density of the passive Q-switch pulse was 16.5 MW/cm². When gadolinium ion was substituted by Dy³⁺ ion, the Dy:GdCOB crystal will emit yellow fluorescent at 585 nm. Yb³⁺ ion has sensitizing effect on other rare-earth ions in GdCOB crystal. The upconversion mechanisms in co-doped GdCOB crystal were discussed.