Efficient Raman shifting of microjoule pulses in N2-filled anti-resonant fiber

We demonstrate efficient frequency down-conversion of femtosecond pulses based on the interplay of Raman-enhanced self-phase modulation and impulsive redshifting in gas-filled anti-resonant hollow-core fiber. With 20 µJ and 140 fs pulses at 1030 nm launched into a short length of fiber, pulses with durations below 100 fs are generated between 1100 and 1300 nm, with over 26% efficiency and above 5 µJ energy, for peak powers between 50 and 100 MW. The modest experimental requirements and highly efficient conversion make this a practical source for wavelength-specific applications.