Due to Yb:CaF2 crystal low quantum defect and a comparably long fluorescence lifetime, ytter-bium-doped gain media are preferably utilized for high-power diode-pumped systems and laser amplifiers with high optical-to-optical conversion efficiencies. From this point of view, Yb:YAG is now the most important and developed one. Just recently, ytterbium-doped alkaline-earth fluori-des (Yb:CaF2) have attracted considerable interest for use in diode-pumped femtosecond (fs) la-sers and amplifiers.
Alkaline-earth fluorides which can be easily grown by using the standard Czochralski or Bridgman technique show a wide optical transmission range, a low dispersion behavior and limited nonlinear effects under intense laser irradiation. It was recently shown that Yb:CaF2 single crystal can be grown up to diameters of about 200 mm, which is superior for high-energy short-pulse lasers with centimeter-sized apertures