Passively Q-switched diode-pumped Nd:YAG and Nd:YVO4 using (Cr4+,Ca2+):YAG and (Cr4+,Mg2+):YAG saturable absorbers

We report the operation of passively Q-switched diode-end-pumped Nd:YAG and Nd:YVO4 lasers by employing Cr4+-doped garnets with Ca2+ or Mg2+ as charge compensators. We found that the laser performance improved significantly, mainly in the Nd:YVO4 system when (Cr4+,Mg2+):YAG sample was used as a passive Q-switching. For example, in the Nd:YVO4 and Nd:YAG lasers, the maximum peak power using (Cr4+,Mg2+):YAG saturable absorber was higher by a factor of 8.5 and 2.6, respectively, relative to (Cr4+,Ca2+):YAG. This fact is attributed to better optical quality of the (Cr4+,Mg2+):YAG sample, as a result of improved dopant distribution and reduced internal stresses inside the saturable absorber crystals. Similar passively Q-switched laser performance can be obtained by using other garnets with an open structure, and hence, with low internal stresses, such as (Cr4+,Ca2+):GGG. We also compared the laser performance of Nd:GdVO4 with the same saturable absorbers and obtained both passive Q-switching and passive mode locking. By using an analytical model with the relevant physical parameters of the laser crystals and saturable absorbers it is possible to optimize the laser performance.