The hard X-ray (>30 keV) continuum from the interaction of a Ti:sapphire/KrF intense femtosecond UV laser (50 mJ, 440 fs, 10 Hz at 248 nm) with a solid has been measured; the intensity on the target is up to 1017 W/cm2. The X-ray with energy of 200 keV has been observed; the temperature of the hot electron from fitting the spectrum utilizing Maxwellian distribution is 67 keV. This is the first measurement of hard X-rays from femtosecond KrF laser–solid interaction.

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