Progress of niobate laser materials

Abstract

Sapphire, garnet, vanadate and tantalate crystal are the most prominent optical materials and play extremely important roles in optics, especially in lasers. Nb element belongs to the same sub-group with V and Ta elements and niobates (LnNbO₄, Ln=Y, Gd and La) with monoclinic structure have been proved as outstanding self-activated phosphor as early as 1960s. Due to their excellent luminescent properties, their investigations have never been interrupted. In the recent years, we focused on the single crystal growth technology of rare-earth doped niobates and a series of rare-earth doped niobate single crystals have been grown successfully using Czochralski method. Meanwhile, their structure, mechanical, luminescent properties and so on have been characterized. Continuous-wave lasers of 0.9 μm, 1.03 μm and 1.06 μm, and passively Q-switched lasers using Cr⁴⁺:YAG as saturable absorber have been generated successfully in Nd- and Yb-doped niobate crystals for the first time, to the best of our knowledge. In this paper, the preparation, characterization and laser performance of niobate crystals at the lasing wavelength of 1 μm, including YNbO₄, GdNbO₄, Gd_1-xY_xNbO₄ and Gd_1-xLa_xNbO₄ single crystals doped with Nd³⁺ and Yb³⁺ are systematically reviewed by highlighting the most recent research progress.