Repeated passes of the pump radiation through the crystal
increase not only the absorption efficiency but also the effective
pump power density. Therefore, the thin disc design is suitable
for quasi-three-level systems like Yb :YAG, which need high
pump power densities to overcome transparency threshold and
efficient cooling at the same time. Because of an additionally
high Stokes efficiency and good thermomechanical properties
of the laser host, Yb :YAG was chosen as presently the most
promising laser material to scale output power of the thin disc
laser up to the kilowatt range