A watt-level fiber-based femtosecond source at 980 nm

In this paper, we present a novel fiber laser system operating at 980 nm that overcomes the limitations related to three-level operation of Yb-doped fiber amplifiers to produce femtosecond pulses. The system is composed of a mode-locked fiber laser producing 4.7 ps at 20 MHz. The pulses then are successively amplified in a polarization-maintained core-pumped fiber amplifier followed by a cladding pumped power amplifier based on a counter-pumped air-clad fiber amplifier. The fiber amplifier was pumped by a high-brightness fiber pigtailed laser diode operating at 915 nm. Self-phase modulation-induced spectral broadening has been achieved after transmission of amplified pulses through an optimized length of passive air-clad fiber spliced to the Yb-doped air-clad fiber. The air-clad enables pump delivery to the active fiber so that the pump power was free-space launched into the passive fiber end. The passive fiber was designed to match the dimensions of the Yb-doped fiber to minimize signal and pump loss.