Diffraction-limited, 10-W, 5-ns, 100-kHz, all-fiber laser at 155 μm

This Letter reports on an all-fiber-integrated master-oscillator, power amplifier system at 1.55 μm producing 5-ns, 100-μJ pulses. These pulses are generated at a 100 kHz repetition rate, corresponding to 10 W of average power. The seed source is a low-power, current-modulated, single-frequency, distributed feedback semiconductor laser. System output is obtained from a standard single-mode fiber (Corning SMF-28). Consequently, the beam is truly diffraction limited, which was independently proven by M2 measurements. Further increase of peak power is limited by onset of significant spectral broadening due to nonlinear effects, primarily four-wave mixing. Numerical simulations based on six-level rate equations with full position- and time-dependence were developed to model propagation of pulses through the amplifier chain. This capability allows minimization of the amplified spontaneous emission, which can be directly measured using a fast acousto-optic modulator to gate the pulses.