Mode-mismatched thermal lens determination of temperature coefficient of optical path length in soda lime glass at different wavelengths

The time-resolved and steady-state mode-mismatched thermal lens technique has been used to determine the temperature coefficient of optical path length ds/dT at different wavelengths of soda lime glasses (72 wt % SiO2, 18 wt % Na2O, 10 wt % CaO, and 70.5 wt % SiO2, 17.5 wt % Na2O, 10 wt % CaO, 2 wt % Fe2O3). The aberrant model, which takes into account the thickness change of the sample and is more realistic than the parabolic treatment when used to describe the thermal lens effect, was used as the theoretical model. The results showed that ds/dT is (2.1±0.1)×10−6 K−1 at 632.8 nm and (2.4±0.1)×10−6 K−1 at 442 nm for the undoped sample and (4.66±0.03)×10−6 K−1 at 632.8 nm and (6.1±0.1)×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 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.