Efficiency of erbium 3-µm crystal and fiber lasers

The population dynamics of erbium 3-μm crystal and fiber lasers are compared experimentally and theoretically. Laser slope efficiencies of 40% in Er:LiYF4 and 23% in a fluorozirconate fiber are experimentally demonstrated under Ti:sapphire pumping. These are both to our knowledge the highest values reported so far for the different host geometries. On the basis of the excitation and loss mechanisms, the best pump wavelengths are determined to be 970 mm in LiYF4 and 791 nm in a fluorozirconate fiber. The theoretical limit of the slope efficiency with respect to absorbed pump power is redefined as depending on the major population mechanisms of the system. Calculated values are 56% in Er:LiYF4 and 27% in a fluorozirconate fiber.