Wavelength tuning of nanosecond pulses in Erbium-doped fluoride fibre amplifier

We investigate the amplification of mid-infrared nanosecond laser pulses in a single-mode Er-doped fluoride fibre amplifier. The seed laser pulses in the wavelength range around 2790 nm are generated in a wavelength-tuneable, PPLN-based OPO, with sub-10 ns pulse durations and pulse energies of few 100 nJ at a repetition rate of 10 kHz. The single-stage fibre amplifier consists of a double-clad, single-mode Er-doped fluoride fibre with a doping concentration of 70000 ppm, pumped at 980 nm in counter-propagation to the laser signal. The sub-10 ns laser pulses are amplified to pulse energies above 35 µJ, resulting in gain values of more than 20 dB and peak powers above 5 kW. The gain bandwidth and wavelength range of the fibre amplifier are investigated at different gain values and wavelength tuning is demonstrated over the range from 2711 nm to 2818 nm.