Recently new interest has developed in upconversion laser pumping, whereby laser output is obtained in transitions of rare earth ions in a variety of hosts that initiate in an ionic energy level higher that can be directly accessed by a single pump photon. This situation can come about through cooperative energy sharing by two or more ions or a sequential absorption process. Levels thus excited can lead to laser emission at both shorter or larger wavelengths than that of the pump. Particularly interesting are visible and UV systems pumped at wavelengths that are available from diode lasers.
© 1989 Optical Society of AmericaPDF Article