Published online by Cambridge University Press: 15 April 2000
Excited state absorption of laser (≅ 1.3 µm, corresponding to the $^4{\rm F}_{3/2}\to {}^{4}I_{13/2}$ laser channel) and pump (790-860 nm) radiation have been investigated in Nd doped YAl3(BO3)4 non-linear laser crystal. Laser gain slope efficiency measurements as a function of pump wavelength have been used to estimate the excited state absorption of pump radiation. On the other hand, excited state absorption cross-section in the 1300−1400 nm wavelength range has been measured by using two beam spectroscopy. We have obtained that excited state absorption cross-section for pump radiation is negligible whereas around 1.3 µm it is comparable to the stimulated emission cross-section from 4F3/2 state, so that the net gain cross-section becomes negative for certain wavelengths.