Enhanced performance of thin-disk lasers by pumping into the zero-phonon line.

Pumping Yb:YAG or Yb:LuAG into the zero-phonon line at 969 nm instead of using the common pump wavelength of 940 nm reduces the heat generation by 32%. In addition to the 3% increase of the Stokes efficiency, this significantly reduces the diffraction losses caused by the thermally induced phase distortions leading to a remarkable increase of the overall efficiency especially of fundamental-mode thin-disk lasers. Using this pumping scheme in an Yb:LuAG thin-disk laser, we achieved 742 W of nearly diffraction limited (M2≈1.5) output power at an unprecedented high optical efficiency of 58.5%. For multimode operation (M2≈15) the maximum optical efficiency of an Yb:YAG thin-disk laser was increased to 72%.