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.