Nd3+ and Lu3+ Doped CaF2 Crystals as Novel Amplifier Materials for High-Energy Infrared Lasers

Within neodymium-doped laser crystals, the doping of fluorite-type single crystals reveal the unique possibility for high-energy laser amplification at 1 mu m, which makes these materials especially appealing to the field of nuclear physics, particularly inertial confinement fusion. In this work, a complete and detailed spectroscopic investigation of CaF2:Nd3+ single crystals co-doped with various concentrations of Lu3+ ions was performed using several spectroscopy techniques. The results show that an increase in Lu3+ concentration tends to increase the Nd3+ transitions' quantum efficiency, as a consequence of the replacement of Nd-Nd clusters by Nd-Lu clusters. By carefully choosing the Lu3+ concentration, the time windows used in time-resolved spectroscopy, the excitation and fluorescence wavelengths, it is possible to isolate the absorption and emission spectra of each type of Nd-Lu clusters (labelled NL1 and NL2) and to further derive absorption and emission cross sections for each active centre. We used the time-resolved excitation spectra to reconstruct the absorption spectra of different samples in which Nd-Nd clusters and the two types of Nd-Lu clusters coexist. Thus we were able to estimate the concentration of each type of Nd3+ centres as a function of the Lu3+ concentration, showing in particular that above 5%Lu3+, all quenched Nd3+ clusters have been replaced by emitting Nd-Lu clusters. Finally, laser operational parameters, such as radiative lifetimes and stimulated emission cross sections have been estimated, and the model has been proved self-consistent by a spectroscopic cross-check procedure.