The temperature coefficient of the optical path length as a function of the temperature in different optical glasses

An interferometric technique was used to determine the temperature coefficient of the optical path length (d S/d T ) as a function of the temperature in several optical glasses. The temperature range was between 25 °C and 180 °C. The studied samples included undoped and doped oxide glasses, such as low silica calcium aluminosilicate, phosphates, borates and also chalcogenides. The oxide glasses had d S/d T between 10 × 10 ⁻⁶ K ⁻¹ and 20 × 10 ⁻⁶ K ⁻¹ , while for the chalcogenides, these were around 70 × 10 ⁻⁶ K ⁻¹. The results showed that d S/d T’s increased with the temperature in all samples. For samples doped with Nd the d S/d T values were found to be independent of concentration. On the other hand, for the phosphate glass doped with Cr, d S/d T increased about 5% when compared with the Nd doped one. In conclusion, the used interferometric method, which is a considerably simpler and a lower cost technique, and is a useful tool to measure d S/d T in semi-transparent glasses as a function of the composition and temperature.