Linear- and nonlinear-optical properties of a new gadolinium calcium oxoborate crystal, Ca_4GdO(BO_3)_3

TLDR

Large, high‑quality Ca₄GdO(BO₃)₃ crystals are grown by Czochralski pulling and are transparent from 0.32 to 2.7 µm with favorable phase‑matching for second‑harmonic generation. Linear and quadratic nonlinear‑optical properties of this new monoclinic biaxial borate crystal are reported. Experimental phase‑matching measurements with a tunable femtosecond broadband source from 0.8 to 2.1 µm are compared with theoretical predictions. The crystal is moisture‑insensitive, exhibits a type‑I effective nonlinear coefficient of 1 pm V⁻¹ in the ZX plane, a 1 GW cm⁻² damage threshold at 0.532 µm, and achieves over 50 % second‑harmonic conversion with a 15‑mm Nd:YAG laser, making it an excellent candidate for next‑generation frequency‑conversion and parametric devices.

Abstract

Large and good-optical-quality crystals of gadolinium and calcium oxoborate, Ca4GdO(BO3)3 (GdCOB) have been grown from a melt by the Czochralski pulling method. The crystal is absolutely insensitive to moisture. Linear- and quadratic nonlinear-optical properties of this new monoclinic biaxial borate crystal are reported. The crystal is transparent in the visible and the near IR (from 0.32 to 2.7 µm), with favorable phase matching conditions for second-harmonic generation. Experimental phase-matching results, measured with a femtosecond broadband pulse parametric generator source tunable from 0.8 to 2.100 µm, are compared with theoretical predictions. The effective nonlinear coefficients are determined, leading to deff=1 pm/V for type I crystals in the ZX plane. The damage threshold is as high as 1 GW/cm2 at 0.532 µm. The second-harmonic generation conversion efficiency of a Q-switched Nd:YAG laser with a 15-mm long crystal is greater than 50%. These values together with the possibility of growing large crystals make GdCOB an excellent candidate for the next generation of crystals for frequency conversion and parametric processes.