Anisotropy of thermal and spectral characteristics in Tm:YAP laser crystals

Thermal expansion coefficients along three main crystallographic axes of Tm-doped YAlO3 (Tm:YAP) single crystals were investigated in the temperature range of 30–1350 °C, and the results showed that they are 11.9458, 5.0012 and 10.5439 × 10−6 K−1, respectively. Polarized absorption and fluorescence spectra of Tm:YAP crystals in a–c directions were measured. The absorption cross sections near 794 nm are 8.64, 9.22 and 6.80 × 10−21 cm2, respectively. According to the fluorescence spectra, the b-axis emission cross section at 1.86 is determined to be 4.33 × 10−21 cm2, larger than those along two other axes. The results above showed that the anisotropy effect of thermal and optical characteristics exists in Tm:YAP crystal and b orientation is the preferred one. The origin and peculiarities of anisotropy were investigated and discussed.