SPECTRUM OF STIMULATED EMISSION DUE TO SELF-SATURATING TRANSITIONS IN HIGH-CONCENTRATION MEDIA.

An investigation was made of various cases of a population inversion between the **4I//1//1/////2 and **4I//1//3/////2 levels in Y//3Al//5O//1//2:Er**3** plus crystals. It is found that when nonradiative transitions from the upper levels to the active levels by the mechanism of multiphonon energy transfer are more probable, laser action occurs due to transitions between the Stark components of the **4I//1//1/////2 and **4I//1//3/////2 levels with the highest oscilator strengths. If nonradiative transitions due to ion-ion interaction are more probable, a ″red shift″ is observed in the lasing spectra.