Add to ORKGInternational audienceThermal and spectroscopic parameters suggest Yb-doped materials and in particular Yb:CaF 2 to be a good choice for diode pumped high power lasers [1-4]. In the frame of the Cilex-Apollon 10PW project we are developing new OPCPA pump sources based on those crystals [5]. We are presenting the last status of high-repetition rate multipass amplifiers based on Yb:CaF 2 developed in this project and how the exact measurement of the thermal lens allows us to optimize the design of the amplifier avoiding beam focusing and then to extract efficiently and reliably the energy without damaging the optics and access safely to a reliable stable regime within a 50 mJ-range