LiB3O5 (LBO) crystals are used to generate the second, third, and fourth harmonics of near-infrared solid-state lasers. At high power levels, the material’s performance is adversely affected by nonlinear absorption. We show that as-grown crystals contain oxygen and lithium vacancies. Transient absorption bands are formed when these intrinsic defects serve as traps for “free” electrons and holes created by x rays or by three- and four-photon absorption processes. Trapped electrons introduce a band near 300 nm and trapped holes produce bands in the 500-600 nm region. Electron paramagnetic resonance (EPR) is used to identify and characterize the electrons trapped at oxygen vacancies (the unpaired electron is localized on one neighboring boron). Self-trapped holes and lithium vacancies with the hole trapped on an adjacent oxygen are also observed with EPR. At room temperature, we predict that most of the unwanted defect-related ultraviolet absorption created by a short laser pulse will decay with a half-life of 29 µs.
Optical Materials Express
B. C. Holloway, C. A. Lenyk, T. D. Gustafson, N. C. Giles, D. Perlov, and L. E. Halliburton, "Oxygen vacancies in LiB3O5 crystals and their role in nonlinear absorption," Opt. Mater. Express 12, 4155-4168 (2022)
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Plain-text title: Oxygen vacancies in LiB3O5 crystals and their role in nonlinear absorption.