Refractive-index dispersion for BaF 2 –GdF 3 –ZrF 4 –AlF 3 glasses

Refractive-index dispersion measurements were performed on bulk specimens of 2-, 4-, or 6-mol % AlF3 doped 33BaF2–4GdF3–63ZrF4 (mol %) glass and 4-mol % LiF, CsF, YF3, CdF2, SnF2, or PbF2 doped 31.68BaF2–3.84GdF3–60.48ZrF4–4AlF3 (mol %) glass in the wavelength region from 0.4047 to 5.3036 μm. The material dispersion curve and zero material dispersion wavelength were estimated on the basis of refractive-index dispersion measurements. The slope of the material dispersion curve for these fluoride glasses was less steep than that for SiO2 glass in the wavelength range estimated. The zero material wavelength λ0 shifted to a shorter wavelength with increasing AlF3 concentration. The λ0 is 1.675 μm for 31.68BaF2– 3.84GdF3–60.48ZrF4–4AlF3 (mol %) glass. When 4-mol % LiF, CsF, YF3, CdF2, SnF2, or PbF2 were doped into these glasses, each λ0 shifted from 1.675 to 1.670, 1.668, 1.673, 1.681, 1.683, or 1.704 μm, respectively. The temperature dependence values of the refractive-index dispersion and material dispersion for 31.68BaF2–3.84GdF3–60.48ZrF4–4AlF3 (mol %) glass were also obtained. The temperature coefficients of the refractive index were negative values (dn/dTrelative = −1.0 × 10−5/°C) and the wavelength dependence of dn/dT was small. The wavelength λ0 shifted from 1.675 to 1.605 μm, due to the rise in the measurement temperature from 25° C to 250° C.