Spatial and pulse shape dependence of K source from high contrast fs laser plasmas in regime of Relativistic Engineering

Chen, L.-M.; Koga, J. K.; Kando, Masaki; Kotaki, Hideyuki; Nakajima, Kazuhisa; Bulanov, S. V.; Tajima, Toshiki; Xu, M. H.*; Li, Y.-T.*; Dong, Q. L.*; Zhang, J.*

Interaction of intense Ti: Sapphire laser with Cu foil targets has been studied by measuring hard X-ray generation. Hard X-ray spectroscopy and K X-ray conversion efficiency () from Cu plasma have been studied as a function of laser intensity via pulse duration scan (60 fs 600 fs), laser pulse energy scan (60 mJ 600 mJ) and target displacement scan from best focus. For intensity I W/cm, the Cu keep on increasing to reach a maximum value of at an intensity W/cm. The focusing is varied widely to give a range of intensities from 10 W/cm W/cm. Comparing to a recent publication, two individual emission peaks are obtained, one is at best focal spot and the other is at larger target offset corresponding to W/cm. Each peak is corresponding to different energy absorption mechanism. In addition, when we introduce slightly detuning of compressor gratings at the best focal condition, it shows generated by negatively skewed 100 fs pulse width laser irradiation reach and almost 7 times greater than the case of positively skewed pulse. Vacuum Heating is greatly stimulated in this case and preciously control of pre-plasma is the key factor in tuning control of X-ray emission in relativistic fs regime.