Asymmetric chirp control by four-wave-mixing in gas-filled hollow capillary fibers

In this study, we demonstrate the antisymmetric transfer of chirp from near-infrared (NIR) ultrashort laser pulses to ultraviolet (UV) pulses through four-wave mixing (FWM) in an argon-filled hollow capillary fiber (HCF). By carefully controlling the gas pressure for phase matching, femtosecond pulses from a Yb:KGW laser and its second harmonic are used to generate an idler UV pulse at a frequency of 3ω via the FWM process (3ω = 2ω + 2ω - ω). Notably, the chirp of the NIR pulses is transferred to the UV pulses with the opposite sign. Under phase-matching conditions, the conversion efficiency exceeds 13%. This work could be used to generate ultrashort UV pulses with arbitrary linear chirp by changing the group delay dispersion (GDD) of the NIR pulses. Especially, negatively chirped UV pulse should have broad applicability because pulses usually suffer from positive dispersion propagating in medium and the pre-compensated UV pulse could solve part of these questions. Both numerical simulations and experiments were conducted to study the chirp transfer in the FWM process.