Kilowatt level transform-limited 150 ns monolithic pulsed fiber laser emitting in the L band

We report on a high peak power pulsed fiber laser emitting in the L band limited by stimulated Brillouin scattering (SBS). On-going developments target at building fiber lasers for CO₂ sensing from space such as ASCENDS emitting at 1572nm. Unfortunately the relevant CO₂ lines compatible with Erbium amplification are located in the L amplification band, where the cross sections are small. Consequently, those fiber sources have low non-linear threshold and low efficiency. The European Space Agency is funding a project dedicated to the design of a high power pulsed fiber laser for CO₂ DIAL monitoring with emission lines located closed to 1579 nm. The system requires 150 ns pulse duration at 4 kHz pulse repetition frequency (PRF). The high precision on the CO₂ concentration measurement requires narrow linewidth and the laser is primarily limited by Stimulated Brillouin Scattering (SBS). SBS threshold can be improved by: reducing fiber length, reducing effective Brillouin gain or increasing effective area. Due to the small cross-sections of Erbium in L band, large doping concentration or large fiber length are required. Large mode area phosphate Erbium-Ytterbium codoped fibers have been used to generate 84 μJ for 1 μs pulses with 1% efficiency which corresponds to ~84 W peak power.