188 W average power coherently combined Tm-doped fiber laser system delivering ultrashort pulses with 1.86 mJ energy

We report on our results of the coherent combination of four Tm-doped rod-type fiber amplifiers. The chirped pulse amplification system emits an average output power of 188 W and a pulse energy of 1.86 mJ at 100.86 kHz repetition rate. The compressed pulses were measured via second order frequency optical gating. The retrieval reveals a compressed pulse duration of the laser system of 84 fs resulting in peak power of 17.7 GW. The amplifier interferometer was stabilized using locking of coherence by single-detector electronic frequency-tagging and piezo driven mirrors in front of the amplifier channels. The long term stability of the source was tracked with a thermal power sensor over a duration of 120 minutes and shows a stability of <0.1 % rms over this measurement period. To the best of our knowledge, this is the highest average power ultrafast mJ-class short-wavelength infrared laser to date. This proves the applicability of coherent combining techniques in Tm-doped fiber laser systems, opening the route towards performance scaling of ultrafast SWIR laser sources to kW-class average power levels with multi-mJ energies. Additionally this renders this technology the ideal candidate for frequency conversion into the soft X-ray, mid infrared and THz spectral region.