Simultaneous Generation of UV Harmonics and Protons From a Thin-Foil Target With a High-Intensity Laser

We observe UV harmonics and protons with a 7.5-mum-thick polyimide target irradiated with a high-intensity Ti:sapphire laser. The laser intensity dependence of UV harmonics and proton signal is measured by varying the distance between the target surface and the best focus of the laser beam. In the case of appropriate condition for proton generation with a maximum energy of ~2.7 MeV, the weak broad spectrum in the UV region is generated. The UV harmonics of up to the fourth order are generated as the target is moved away from the best focus position. In this condition, the maximum energy of protons is reduced to ~1 MeV. The simultaneous generation of the harmonics and protons is observed at the amplified spontaneous emission intensities between ~5 times 10¹¹ and ~5 times 10¹² W/cm².