DIRECT UPPER-STATE PUMPING OF THE 2.8 MU-M ER-3+-YLF LASER

Direct resonant pumping of the 4I11/2 upper state of the 2.8-mu-m Er3+:YLF laser at 0.97-mu-m is shown to be more efficient than other pumping schemes which have been used for this transition. Upper-state pumping avoids nonradiative losses arising from phonon and self-quenching decays inherent in other pumping schemes. Efficient performance of the 2.8-mu-m laser is maintained on condition that extremely shallow pump absorption is avoided. Reduced efficiency for shallow pump absorption is attributed to upconversion loss arising from high pumping rates.