Processes of heat generation in Nd+3 doped materials during pump-lase cycle

A study of the various channels of energy transfer from the upper lasing level of Nd:YVO 4 following direct pumping at 880nm is presented. The dependency of the heat that was generated in the laser crystals as a function of doping concentrations and different pumping and lasing conditions was measured along with the laser performance. In the absence of a laser resonator, the heat to pump power relation behaved linearly and was strongly dependent upon the Nd +3 doping concentration. During lasing at 1064nm, the heat to pump ratio dropped dramatically but still did increase linearly with growing concentrations. The heat to pump dependency upon different output couplers with the same laser crystal was ~linear too and increased with increasing intra-cavity power density. These experimental results suggest that different mechanisms govern the heat creation before and after laser threshold. Cross relaxation on top of the Stokes shift seems to govern heat creation before threshold, while excited state absorption and crystal impurities may be the mechanisms that govern the excess heat creation above threshold.