Sub-40-fs diode-pumped ytterbium-doped mixed rare-earth calcium oxoborate laser

We present a detailed comparative investigation of the continuous-wave and mode-locked laser performance of a mixed rare-earth calcium oxoborate crystal, Yb:(Gd,Y)Ca₄O(BO₃)₃, abbreviated as Yb:(Gd,Y)COB, for all three principal optical polarizations. Pumped by a low-power, single-transverse-mode, fiber-coupled laser diode at 976 nm, the Yb:(Gd,Y)COB laser generated soliton pulses as short as 32 fs at 1052.4 nm via soft-aperture Kerr-lens mode-locking, delivering an average output power of 51 mW at ∼66.2 MHz for light polarization E || Z. For light polarization E || Y, slightly longer (34 fs) pulses were directly generated at 1053.7 nm, with a higher average output power of 86 mW at ∼66.7 MHz. To the best of our knowledge, these results represent the shortest pulses ever achieved from any Yb³⁺-doped borate crystal.