All-fiber GHz few-cycle pulse generation at 2 µm

We demonstrate an all-fiber GHz mode-locked laser system with few-cycle duration operating at 2 µm. Based on a dispersion-managed mode-locked oscillator, a multi-stage fiber amplifier, and a nonlinear pulse compressor, the laser system can deliver watt-level few-cycle pulses at a fundamental repetition rate of 1.041 GHz. This 2-µm pulsed laser offers outstanding performance metrics, including a pulse duration of 33 fs (corresponding to ∼5 optical cycles) and an average power of 4.17 W. Moreover, the all-fiber laser system exhibits excellent power stability, and the integrated relative intensity noise (RIN) is only 0.052% (10 Hz–1 MHz). It is anticipated that this new, to the best of our knowledge, laser source is promising for frontier applications, including coherent supercontinuum generation, nonlinear frequency conversion, and laser–material interaction.