Diode-pumped self-starting mode-locked femtosecond Yb:YCa ₄O(BO₃)₃ laser

A self-starting mode-locked femtosecond laser is accomplished with an oxoborate self-frequency doubling crystal Yb:YCa4O(BO3)3 (Yb:YCOB) as the gain medium and a semiconductor mirror as the saturable absorber. Pumped by a 976-nm fiber-coupled diode laser with 50-μm core diameter, stable mode-locked laser pulses up to 430 mW were obtained at a repetition rate of 83.61 MHz under 5-W pump power. The autocorrelation measurement shows that the pulse duration is as short as 150 fs by assuming the sech² pulse shape at a central wavelength of 1048 nm. This work has demonstrated a compact and reliable femtosecond laser source for prospective low-cost applications.