Octave-spanning supercontinuum from an efficient gigahertz femtosecond Yb:KGW laser with 2.2-W average power

This paper presents a very efficient and compact passively SESAM-mode locked Yb:KGW laser oscillator with the highest peak power (6.7 kW) ever obtained for a gigahertz femtosecond diode-pumped solid-state lasers (DPSSL). At a repetition rate of 1.01 GHz the laser generates pulses as short as 290 fs with an average output power of 2.2 W. The spectral bandwidth is 4.8 nm at a center wavelength of 1042 nm and the time-bandwidth product is 0.383, which is close to the ideal theoretical value of 0.315. The slope efficiency is 44% and the optical-to-optical efficiency is 38%. A major challenge of mode locking at high repetition rates is to prevent Q-switched mode locking. Stable and self-starting continuous-wave (cw) mode locking was achieved with an optimized SESAM design and a small mode area in the gain material. A high brightness tapered diode laser with a nearly diffraction limited beam with a lateral beam propagation factor of M²_1/e2 =1.1, containing more than 70% of the power in the central lobe was used. This enabled an average pump radius of ≈ 38 μm at a pump power of 5.9 W with an electrical consumption of less than 25 W. Very recently, the repetition rate was further increased to 2.4 GHz, at an average power of 2.3 W and a pulse duration of 293 fs.