Figure-8 mode-locked Yb-doped fibre oscillator with a nonlinear amplifying loop mirror and power amplification

Abstract We report an all-polarization-maintaining Yb-doped fibre (YDF) femtosecond (fs) laser source at ∼1 µ m comprising a figure-8 mode-locked oscillator and two YDF amplifier stages. By employing a nonlinear amplifying loop mirror, we could achieve dissipative soliton mode-locking with an output of 24.6 mW at a repetition rate of 6.2 MHz. In our experiments, a Raman signal of 16% in the pulse energy helps to obtain stable mode-locked operation in the figure-8 oscillator. The dissipative soliton pulse from the oscillator is stretched by a chirped fibre Bragg grating and is amplified by a two-stage YDF amplifier. After compression, the YDF master-oscillator power-amplifier system yields fs pulses with a pulse energy of 2.3 µ J and a pulse duration of 274.6 fs at a repetition rate of 0.52 MHz. The output pulse energy is limited by the third-order nonlinearity of the fibre amplifier chain. Prospects for further pulse energy scaling are discussed.