Measurement of thermal refractive index coefficients of nonlinear optical crystal RbBe2BO3F2

• Temperature-dependent refractive indices of RBBF crystals are measured.
• Thermo-optic dispersion equations of RBBF crystals are derived.
• Temperature-dependent phase matching angles for SHG of RBBF crystals at 266 nm are reported.

The principal refractive indices of RbBe2BO3F2 (RBBF) crystal at wavelengths of 0.194, 0.254, 0.363, 0.405, 0.435, 0.546, 0.644, 0.706, and 1.014 μm are accurately measured by using the vertical incidence method within the temperature range from 24 to 160 °C. Equations of thermal refractive index coefficients as a function of wavelength that could be used to calculate the principal thermal refractive indices at different wavelengths are derived. Moreover, experimental phase-matching angles for second harmonic generation of RBBF at 266 nm wavelength at different temperatures as well as the theoretical values built on our experiment results are also given.