INVESTIGATIONS ON THE SLOPE EFFICIENCY OF A PULSED 2.8-MU-M ER3+LIYF4LASER

A slope efficiency of 40% from an Er3+:LiYF4 laser is demonstrated und er pulsed Ti:sapphire pumping at 973 nm. With reduction of the pump-pu lse duration a significant decrease of the slope efficiency and an inc rease of the threshold is observed in the experiment and confirmed wit h high accuracy in a computer simulation. This behavior is due to inte rionic upconversion from the lower laser level, which leads to energy recycling into the upper laser level. The upconversion rate is negativ e at threshold but increases strongly with rising pump-pulse energy, t hus enhancing the slope efficiency. The conditions are derived that ar e necessary for achieving the high slope efficiency of the energy-recy cling regime. (C) 1997 Optical Society of America.