Highly efficient nonlinear compression of mJ pulses at 2 µm wavelength to 20 fs in a gas-filled multi-pass cell

Abstract

Within this work we demonstrate the highly efficient nonlinear spectral broadening and subsequent temporal compression of 1.49 mJ pulses at 101 kHz repetition rate from an ultrafast thulium-doped fiber laser system employing a gas-filled multi-pass cell. To achieve spectral broadening, we use a krypton and helium-filled Herriott-type multi-pass cell with highly reflective broadband dielectric mirrors. The spectrally broadened pulses are subsequently compressed using fused-silica plates, resulting in a pulse duration of 20 fs and an overall excellent transmission of 96%. Furthermore, the beam quality is preserved up to the maximum output power of 144 W. It provides, to the best of our knowledge, the highest average power with few-cycle pulses at 2 µm wavelength with almost 10 times more pulse energy and 3 times more average power than previous 2-µm multi-pass cells, enabling future secondary source experiments.