Sub-70 fs Kerr-Lens Mode-locked Yb:CaF2 laser oscillator delivering up to 2.3 W

Calcium fluoride has raised a great interest in the laser community since its revival in 2004 [1,2] when it has been doped with ytterbium ions. Thanks to its broad emission bandwidth, its good thermal properties and its strong energy-storage ability, Yb:CaF₂ is particularly suitable for high-energy, high-power femtosecond laser systems [2,3]. Nevertheless, due to the very long lifetime of Yb:CaF₂ and its low nonlinear refractive index (1.6 10^-20 m²/W), the stable sub-100-fs mode-locking operation (ML) of Yb:CaF₂ remains challenging and very few works have reported operation in this regime [4]. Up to now, the ML of Yb:CaF₂ oscillators has only been achieved using a saturable absorber mirror to produce stable femtosecond pulses. We report, to the best of our knowledge, on the first demonstration of sub-70 fs pulses Kerr Lens Mode locked oscillator in Yb:CaF₂ by means of a high-brightness pump source [5].