54 W nanosecond Yb-doped all-fiber amplifier at ultra-high repetition rate (tens of MHz) based on mode-locked fiber oscillator and single-mode fiber stretcher

Abstract

We report on a nanosecond all-fiber amplifier with repetition rate of tens of MHz. It is based on a passively mode-locked fiber oscillator at 1064 nm, which has a pulse width of 28 ps and repetition rate of 27.7 MHz. The single-mode fiber with length of 8 km is adopted as a fiber stretcher, in which new frequency components are introduced by strong nonlinear effect such as self-phase modulation, resulting in the broadening of spectral bandwidth from 0.4 nm to around 20 nm. The group-velocity dispersion of the 8 km fiber stretcher is −38 ps (nm km) −1, which stretches the pulse duration of the picosecond pulse to 1–7 ns. At the repetition rate of 27.7 MHz, an average power of 54 W is demonstrated with pulse width of 1.3 ns, and 21 W is achieved with pulse width of ∼5 ns, which have optical-to-optical conversion efficiencies of 41.2% and 30.1% respectively. This all-fiber amplifier based on the passively mode-locked fiber oscillator and 8 km single-mode fiber stretcher is capable of delivering nanosecond pulses while maintaining an ultra-high repetition rate of tens of MHz.

Compact 15 mJ Fiber–Solid Hybrid Hundred-Picosecond Laser Source for Laser Ablation on Copper

“…The SPM-induced spectrum broadening is proportional to the maximum nonlinear phase shift Фmax, which is given by Фmax = γP0Leff, where γ is the SPM is a nonlinear effect produced by picosecond pulsed lasers in the amplification, especially in fiber lasers. The SPM-induced spectrum broadening is proportional to the maximum nonlinear phase shift φ max , which is given by φ max = γP 0 L eff , where γ is the nonlinear coefficient, P 0 is the peak power of the incident pulses, and L eff is the effective length of the fiber [30]. Therefore, the nonlinear phase shift is proportional to the intensity of the incident pulses, which can be significant accumulated in high-peak-power lasers.…”