High power and high energy monolithic single frequency 2 μm nanosecond pulsed fiber laser by using large core Tm-doped germanate fibers: experiment and modeling

We report a high power and high energy all-fiber-based single frequency nanosecond pulsed laser source at similar to 1918.4 nm in master oscillator-power amplifier (MOPA) configuration. The pre-shaped pulsed fiber laser seed with a variable pulse duration and repetition rate were achieved by directly modulating a continuous wave (CW) single frequency fiber laser using a fast electro-optical modulator (EOM) driven by a arbitrary waveform generator (AWG). One piece of single mode, large (30 mu m) core, polarization-maintaining (PM) highly thulium-doped (Tm-doped) germanate glass fiber (LC-TGF) was used to boost the pulse power and pulse energy of these modulated pulses in the final power amplifier. To the best of our knowledge, the highest average power 16 W for single frequency transform-limited similar to 2.0 ns pulses at 500 kHz was achieved, and the highest peak power 78.1 kW was achieved at 100 kHz. Furthermore, mJ pulse energy was achieved for similar to 15 ns pulses at 1 kHz repetition rate. Theoretical modeling of the large-core highly Tm-doped germanate glass double-cladding fiber amplifier (LC-TG-DC-FA) is also present for 2 mu m nanosecond pulse amplification. A good agreement between the theoretical and experimental results was achieved. The model was also utilized to investigate the dependence of the stored energy in the LC-TGF on the pump power, seed energy and repetition rate, which can be used to design and optimize the LC-TG-DC-FA to achieve higher pulse energy. (C) 2012 Optical Society of America