Spectral combining of pulsed fiber lasers: scaling considerations

We show spectral combination of pulsed fiber laser systems for the first time to our knowledge. In this proof of principle experiment, two directly modulated wavelength-stabilized tunable external cavity diode lasers (ECDL) serve as independent seed sources. Each signal is amplified in a two stage ytterbium-doped fiber amplifier. The spatial overlap is created using a transmission grating with a combining efficiency as high as 92%. No beam quality degradation has been observed for the combined beam compared to a single emission. An electronic delay is used to adjust the temporal overlap of the pulses from the spatially separated amplifier setups. The presented approach offers an enormous scaling potential of pulsed fiber laser systems, which are generally limited by nonlinear effects or fiber damage. We show that the huge gain bandwidth of Yb-doped fiber amplifiers and the high diffraction efficiency of dielectric reflection gratings in this wavelength range yield potential for a combination of up to 50 channels. For state-of-the-art ns-amplifier systems > 100 MW of peak power, > 100 mJ of pulse energy and average powers of > 10 kW seem feasible.