Transverse scattering of radiation upon focusing of pump laser beam to line in experiments on X-ray laser

We present the results of experimental studies of the parameters of scattered radiation of a photo-dissociation iodine laser that is focused in a line onto a flat target made of germanium or zinc. At laser radiation intensities above 1013 W/cm2, an anomalously strong scattering in the direction of the line is observed in the form of narrow beams with a divergence of 5–10 mrad. In this case, the scattered energy is estimated to be 70–120 J, which corresponds to 30–50% of the total energy of the laser beam. This scattered radiation appears only in the presence of a prepulse with an intensity of no lower than 1011 W/cm2 that is emitted ∼5 ns earlier than the main laser pulse. At lower intensities of the prepulse, no anomalous scattering of radiation is observed, which indicates that the preliminary action of the laser radiation on the target plays a decisive role in the scattering mechanism.