A thermal lens study of undoped and Fe₂O₃-doped silicate glasses at different wavelengths

Abstract
The mode mismatched thermal lens technique has been wed to determine the temperature coefficient of optical path length, ds/dT, of undoped and 2% Fe₂O₃-doped silicate glasses, at different wavelengths. The aberrant model, which takes into account the thickness change of the sample, was used as the theoretical model. The results showed that ds/dT is (2.1 ± 0.1) x 10^-6 K^-1 at 632.8 nm and (2.4 ± 0.1) x 10^-6 K^-1 at 442 nm for the undoped sample and (4.66 ± 0.03) x 10^-6 K^-1 at 632.8 nm and (6.1 ± 0.1) x 10^-6 K^-1 at 442 nm for the iron doped sample. The greater value of this parameter found for the doped sample at the Fe³⁺ absorption band (442 nm), was associated with the bigger value of the temperature coefficient of the electronic polarizability caused by the presence and environment of Fe³⁺ iron in the structure of the glass.