For second-order nonlinear-optical processes in the ultraviolet, appropriate materials with a sufficiently large band-gap typically exhibit smaller nonlinear coefficients than materials with comparably smaller band-gap. Whispering gallery resonators, with their outstanding quality factors, provide field enhancement and can compensate for these small coefficients. We report on the successful fabrication of a whispering gallery resonator made of lithium tetraborate, a suitable material for ultraviolet applications with a small nonlinear coefficient of d₃₁ = 0:073 pm/V. Quality factors of the order of 108 are observed from the ultraviolet to the near-infrared spectrum. The inferred absorption coefficients of lithium tetraborate are below 0.2 m^-1 in the visible and near-infrared. Continuous-wave second harmonic generation from 490 nm light to 245 nm is observed with conversion efficiencies up to 2.2 %.

Date Published: 27 February 2015
PDF: 6 pages
Proc. SPIE 9347, Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XIV, 93470A (27 February 2015); doi: 10.1117/12.2079829

Published in SPIE Proceedings Vol. 9347:
Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XIV
Konstantin L. Vodopyanov, Editor(s)