The paper discusses the spectral-broadening processes of femtosecond pulses in the high-frequency region when optical breakdown occurs in a gaseous medium. It is shown that the spectrum of the generated high-frequency radiation contains several isolated maxima whose positions are determined by the properties of the medium and by the thickness of the layer of gas. An illustration is given of the role of taking into account the dispersion of the nonlinear refractive index in the high-frequency region of the optical range of the spectrum when optical breakdown is being modelled. The results of the modelling are compared with experimental data from an investigation of the optical breakdown of a layer of sulfur hexafluoride.
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