The general principle is illustrated by the three-level laser of Figure 12.3.4(a), for which the optical laser pump radiation driving the 1,3 transition is so strong that it roughly equalizes N 1 and ...The general principle is illustrated by the three-level laser of Figure 12.3.4(a), for which the optical laser pump radiation driving the 1,3 transition is so strong that it roughly equalizes N 1 and N 3 . The key to this laser is that the spontaneous rate of emission A 32 >> A 21 so that all the active atoms quickly accumulate in the metastable long-lived level 2 in the absence of stimulation at f 21 . This generally requires D 32 >> D 21 , and finding materials with such properties for a desi…
