Excitation mechanisms for upconversion lasers

A number of nonlinear upconversion excitation mechanisms have been used to achieve lasing at wavelengths that are shorter than those of the pump light. We found that sequential two-step absorption was the principal process in YAlO3+ and LaF3+ whereas energy transfer upconversion dominated in YLiF4+. A nonlinear absorption process associated with cross relaxation resulted in upconversion lasing in YLiF4+. © 1990.