we report the generation of sub 20 fs UV pulses with 300 μJ energy at 1 kHz repetition rate by applying spectral broadening of the UV pulses during filamentation in argon. The original UV pulses, applied in the experiment, are generated as the third harmonic (TH) of an amplified Ti:sapphire laser system at 268 nm. The THG stage is pumped by the fundamental frequency (FF) of a regenerative/multipass Ti:sapphire amplifier at 805 nm. The laser provides up to 12 W of average power at 805 nm with 135 fs pulse duration and 1 kHz repetition rate. In this experiment 7 mJ of the FF pulse energy was applied. The generated TH pulse energy exceeds 1 mJ and the duration is 100 fs
