132 W, 1.3 mJ, sub-two-cycle pulses at 1.8 μm wavelength

Few-cycle laser systems in the short-wavelength infrared (SWIR) region (from 1.4 µm to 3 µm) with high pulse energy and high average power have become increasingly impactful as driving sources for THz, mid-infrared and soft X-ray generation with numerous subsequent applications. Compared with the well-established near-IR region, the longer wavelength enables higher conversion efficiency in the THz and mid-infrared generation, and is considered as a favorable tradeoff between pushing the high harmonic generation phase matching cut-off up to the water window region (300 eV - 500 eV) while maintaining reasonable single emitter efficiency. In this contribution, we present our first results of the nonlinear post compression of a high-power ultrafast thulium-doped fiber laser output in a 1.05 m long rod-type hollow-core fiber filled with ~3 bar argon. With around 90 fs input pulse duration (FWHM) and 180 W input average power, the nonlinear compression stage delivers compressed pulses with a duration of 10.2 fs (FWHM), an average output power of 132 W. This corresponds to 1.3 mJ pulse energy at a repetition rate of 101 kHz and 1.64 cycles at a central wavelength of 1.87 µm. With this, we estimate a compressed pulse-peak power of about 80 GW, with an energy content of ~66% in the main feature. It is the highest average power mJ-class few-cycle source in the SWIR region reported to date. Featuring a unique combination of peak- and average-power with less than 2 cycle pulses, this laser source is highly interesting for nonlinear frequency conversion addressing THz, mid-infrared and soft X-ray region.