TG–DTA properties of new nonlinear optical materials: K2Ln(NO3)5·2H2O (Ln=La, Ce, Pr, Nd, Sm) Original Research Article

An interferometric method was used for the determination of refractive index of glassy SiO2 in the infrared (IR) wavelength region at temperatures ranging from 23.5 to 481°C by IR spectroscopy. The refractive index was found to increase with temperature at a given wavelength. Irregularities of the thermal coefficient of the refractive index (dn/dT) with temperature were observed and explained by the existence of crystal-like microstructures in silica glass. Optical dispersion (dn/dλ) exhibits a maximum at a given temperature. The wavelength at the maximum depends on temperature, showing irregularities with temperature like the thermal coefficient of refractive index.