Ultrashort 198- and 158-nm pulses are generated simultaneously by cascaded four-wave mixing of the second and third harmonics of a 80-fs Ti:Sapphire laser in filamentation propagation through a single Ar gas cell. The energies of the 198- and 158-nm pulses are 7.6 μJ and 600 nJ, respectively. The duration of 198-nm pulse is determined to be ca. 45 fs by transient-grating frequencyresolved optical grating, which indicates that the pulse is intrinsically transform limited and chirped by the rear window of the gas cell. The spectral bandwidths of 198- and 158 nm support the transform limited pulse durations of 40 and 28 fs, respectively.
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