Fluorescence quantum efficiency and Auger upconversion losses of the stoichiometric laser crystal NdAl3(BO3)4 -: art. no. 235111

Multiwavelength thermal lens technique has been carried out to determine the fluorescence quantum efficiency of Nd3+ ions in the NdAl3(BO3)(4) stoichiometric microchip laser crystal. The value obtained for the quantum efficiency, around 0.30, is an anomalously high value when compared with other Nd3+ stoichiometric crystals. Other parameters of great relevance in the laser performance (such as thermal diffusivity, thermal conductivity, and temperature induced path length change) have been also estimated. From the analysis of thermal lens measurements under different excitation intensities we have obtained the upconversion parameter. By comparing this experimental value with that calculated from the microscopic theory we have been able to determine the energy migration assisted upconversion as the dominant mechanism, in the excitation power regime used. Finally, we have concluded that energy transfer upconversion processes strongly reduce the metastable quantum efficiency constituting a non-negligible heat source in strongly pumped NdAl3(BO3)(4) crystals.