A Ti:sapphire based laser system provided 30-fs pulses centered at 800 nm with up to 3 mJ energy was used in the experiment. The input beam was focused by a concave mirror with radius of 3 m into a 1.5 m long glass cell. No iris-diaphragm or other beam reshaping tools were used for filament adjustment. The gas cell was filled with SF6 or for comparison with Ar at variable pressure of 0.1–0.7 bar. After the filament start point the laser radiation was spatially confined and propagated through the entire gas cell. Diameter of central, bright part of the beam was in a range of 2 mm directly after the output window. The output spectra recorded directly after the cell filled gases are shown in Fig. 1. The filament in SF6 demonstrate qualitatively different spectral shape, as compared to Ar, with dramatic enhancement in frequency conversion out of fundamental spectral range especially towards the higher-frequency domain. FWHM of the detected spectrum reached almost octave bandwidth of 440–875 nm.
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