To evaluate in first
instance the impact on the device performance of the reverse cross-relaxation
parameter, we calculated the required pump intensity to reach a given value of  population inversion. This is only a first indication since in
laser or amplifier operation other pehomena may interplay with reverse
cross-relaxation, like photodarkening, since pathways involve population of Tm
levels affected by reverse cross-relaxation (Millar et al. 1988, Broer, Krol, and DiGiovanni 1993, Taccheo et al. 2011, Jetschke et al. 2013, Lupi et al. 2016). Fig. 2
shows, for sample T4, the results for inversions from 0% to 50%. The inversion
is defined as the difference between N2 and N1 (N2-N1)
normalized to the doping concentration.