Thermal lens spectroscopy through phase transition in neodymium doped strontium barium niobate laser crystals

In this work the anisotropic thermal lens (TL) effect was studied in Nd3+ doped SrxBa1−xNb2O6 crystals with two different stoichiometries (x=0.47 and 0.61). TL measurements were carried out as a function of temperature from 30 up to 140°C so that the effect of phase transition was investigated. A strong enhancement in the TL effect during the ferro-to-paraelectric phase transition has been observed. Additionally, we have found an inversion of the TL signal with the crystal stoichiometry. This fact is explained in terms of a different thermal expansion along the c axis for both crystals, as measured by x-ray diffraction experiments. The obtained results open the possibility to tailor a crystal stoichiometry that minimizes the TL effects.