Refractive index dispersion and Raman scattering spectra of a germanium single crystal enriched with $^{70}$Ge isotope

The spectral dependence of the refractive index (RI) of a germanium single crystal enriched in the isotope $^{70}$Ge ($>$ 99.92 at.%) in the spectral range 5500–500 cm$^{-1}$ (1.8–20 $\mu$m) was measured. The data obtained are compared with the results for single crystals of other germanium isotopes ($^{72}$Ge, $^{73}$Ge, $^{74}$Ge, $^{76}$Ge). In the entire studied range, the refractive index values of $^{70}$Ge are higher than for heavier isotopes. This confirms the previously identified trend towards an increase in the RI with a decrease in the atomic mass of germanium isotopes. The Raman spectra of first- and second-order light scattering of a $^{70}$Ge single crystal at a temperature of 293 K.