Optimal concentration of active particles in four-level and quasi-four-level laser systems

The population of the active levels in both CW and pulsed regimes as functions of the concentration of the active impuritie's is deduced by means of the luminescence decay curve. A method is proposed for the determination of the optimal concentration of active impurities with a view to maximizing net transition population from the upper laser energy level to the lower one for the four-level and quasi four-level system. For the four-level system, the optimal concentration of Nd3+ ion in Nd:YAG is calculated and compared with the experimental results. For the quasi-four-level system, the optimal concentration of Tm3+, Tb3+ ions are calculated to be 2.42 at % 0.21 at % for CW regime and 14.14 at % 1.82 at % for pulsed regime (the width of the pulse being 40 mus) in LiYF4 crystal.