  We report on the realization of an all-fiber laser source that delivers
single-frequency pulses at 1645 nm, on a linearly polarized single-mode beam,
based on stimulated Raman scattering in passive fibers. The pulse energy
reaches 14 $\mu$J, for a repetition rate of 20 kHz, and the spectral linewidth
is 9.5 MHz, almost Fourier-transform limited for the 100 ns square pulses. To
the best of our knowledge, this energy is the highest reported at 1645 nm in an
all-fiber laser source. Our method consists in reducing the stimulated
Brillouin scattering (SBS) gain for the pump and signal pulses, respectively by
sweeping the optical frequency of the pump beam, and by applying a strain
gradient on the amplification fiber. This compact laser source is now used in a
transportable lidar system to measure simultaneously wind velocity and methane
(CH4) concentration.
