Thermo-optical effects in diode end-pumped Yb-doped laser crystals and sesquioxide ceramics.
In this work we experimentally determined values of focal length for thermal lenses in diode end-pumped Yb<sup>3+ </sup>:<sup> </sup>YVO<sub>4</sub>, Yb<sup>3+ </sup>:<sup> </sup> Gd<sub>0.64</sub>Y<sub>0.36</sub>VO<sub>4</sub> crystals and Yb<sup>3+ </sup>:<sup> </sup>Y<sub>2</sub>O<sub>3</sub>, Yb<sup>3+ </sup>:<sup> </sup>Sc<sub>2</sub>O<sub>3</sub> laser ceramics. A chosen method for determination of thermal lens in solid state laser media as a function of pump power was based on measurement of a focal point displacement. In theoretical calculations of focal length of thermal lens we took into account effects of temperature and stress-dependent variations of the refractive index and distortion end faces of crystal. Data of focal lengths for thermal lenses in vanadate crystals and Yb<sup> </sup>:<sup> </sup>Y<sub>2</sub>O<sub>3</sub>, Yb<sup> </sup>:<sup> </sup>Sc<sub>2</sub>O<sub>3</sub> ceramics were obtained for the first time. Results were used for creation of terawatt femtosecond laser system with a repetition rate of 1 kHz.