Very Low Threshold CW Excitation of Superfluorescence at 2.72 μm in Er 3+

Several evidences, typical of a superfluorescence effect, have been obtained for the first time under continuous excitation. Emission from Er3+ in LiYF4 at 10 K is obtained at 2.72 μm with a threshold of ≃ 3 mW of absorbed power at 6470 Å.