Single-frequency erbium-doped fiber amplifier with high energy gain at low repetition rates

We report pulse energy of 1.6 mJ at 1 kHz repetition rate from a single-frequency fiber amplifier with high energy gain of 19 dB at 1560 nm, using a 2.4 m long, Very-Large Mode Area (VLMA) Polarization-Maintaining (PM) erbium-doped fiber with 50 μm core diameter and absorption of 50 dB/m, core-pumped with a CW, 1480 nm Raman fiber laser. The in-pulse power fraction was 85%. The FWHM of the output pulses was 1.48 μs at 1 kHz repetition rate. At 150 Hz repetition rate, of interest in coherent wind LIDAR systems, we report 1 mJ, with energy gain of 17 dB, in-pulse power fraction of 72%, and FWHM of 1.24 μs. Stimulated Brillouin scattering limited the maximum energy reported here. The output of the fiber amplifier was diffraction limited, with mean beam quality factor, M², of 1.04. The polarization extinction ratio exceeded 20 dB.