Spectrum broadening of ultrashort ultraviolet pulse in dual-color laser field
双色场下紫外超短脉冲的频谱展宽

When collinear dual-color intense laser pulses are overlapped in time, a strong coupling interaction occurs between their plasma filaments. Due to the cross phase modulation, strong non-linear effects are generated and the spectrum width of the ultrafast ultraviolet (UV) pulse is further broadened. The original UV pulse with a bandwidth of 1.5 nm and energy of 0.45 mJ is obtained by tripling the frequency of a Ti:sapphire laser system. The UV pulse and the near inferred pulse of 7.1 mJ can induce plasma filaments separately after focusing within an argon gas cell, leading to an obvious modulation of the UV spectrum. The full width at half maximum of UV spectrum increases to 6.4 nm which is 4 times the width of spectrum before focusing and 2.5 times the width of single ultraviolet filament broadening. In this experiment, we mainly study the frequency spectrum evolution of dual-color co-filament in argon gas under the condition of different time delays, coupling locations and gas pressures. Optimizing these factors can yield a valid approach to achieving extremely ultrafast pulses in the range of ultraviolet.