Recent advances in rare earth-based borate single crystals: Potential materials for nonlinear optical and laser applications

Due to an increase in the requirement for ultraviolet and visible laser sources nonlinear optical crystals are gaining importance. Borate-based nonlinear optical crystals such as lithium borate LiB3O5 (LBO), CsLiB5O10 (CLBO), SrBe2B2O7 (SBBO), KBe2BO3F2 (KBBF) and K2Al2B2O7 (KAB) have excellent transmission ranges extending from the ultraviolet into the infrared region. But their hygroscopic nature retards their use in real-time applications. Rare earth-based borate crystals such as rare earth calcium oxy borate RECa4O(BO3)3 (RECOB) and rare earth calcium borate RE2CaB10O19 (RECB) have excellent nonlinear optical behaviour and also allow the substitution of ‘laser-active’ ions to create ‘laser crystals’. Further they are non-hygroscopic which favours them in practical applications. A review on RECOB and RECB crystals is presented along with a discussion on our attempts to grow yttrium calcium oxy borate YCa4O(BO3)3 (YCOB), lanthanum calcium oxy borate LaCa4O(BO3)3 (LCOB), yttrium calcium borate Y2CaB10O19 (YCB) and lanthanum calcium borate La2CaB10O19 (LCB) crystals. These crystals possess excellent transmission properties combined with nonlinear optical behaviour. They also exhibit high laser damage threshold (LDT) values.