Alternative approaches for highly efficient diode-pumped lasers

Yb3+-doped gain media are promising candidates for high efficient lasers since they have a broad spectrum, a long fluorescence lifetime, a quantum efficiency close to one and they can be pumped directly by laser diodes. Nevertheless even the heating of those laser media causes problems like thermal lenses, limited average output powers due to thermal destruction and huge cooling efforts. One promising method to reduce the thermal load in the laser medium is the usage of cryogenic amplifiers. This paper shows the changes absorption and emission spectrum for Yb:CaF that allows diode pumping at 980 nm and lasing at 922 nm and thus decreases quantum defect to about 1%. This allows the construction of a laser with a theoretical Stokes limit for the slope efficiency of 99% and thus extremely high potential for very efficient laser operation. In this way the laser medium barely heats up during the laser process.