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

We experimentally demonstrate chirp transfer from NIR ultrashort pulses to UV through four-wave-mixing (FWM) in gas-filled hollow-capillary-fiber (HCF) . Femtosecond pulses from Yb:KGW laser fundamental radiation (ω) and its 2nd harmonic (2ω) are used to generate an idler UV pulse of the frequency at 3ω by the FWM process 3ω=2ω+2ω-ω. Chirp of the NIR pulses can be transferred to the UV pulses with the opposite sign. The conversion is over 13% for the FWM process under the phase-matching gas pressure when the HCF is filled with argon gas. Along with experimental results, we present principles and numerical calculations for this frequency mixing and pulse shaping regime to enable applications in indirect chirp control and spectral modification.