Abstract

Upconversion excitation processes can be used to obtain laser operation at wavelengths that are shorter than that of the pump source. Efficient operation of such lasers is possible in materials with metastable intermediate energy levels that act as population storage reservoirs. Excitation of higher levels that emit short-wavelength radiation can occur by absorption of a second photon from the intermediate level, or by energy transfer processes involving two ions in an intermediate state. Stimulated emission by upconversion excitation using flashlamp pumping was fust reported in 1971.¹

© 1988 Optical Society of America