The Evolution of the Nanowire Array under the Influence of Prepulse of Intense Femtosecond Laser and Its Consequences on the K α Production

The quasi-monochromatic Kα source based on the intense ultra short pulse laser is one of the attractive research topics in the short pulse laser applications. Using relatively simple setup, it is possible to produce bright hard x-ray line emission from several keV to a few tens keV with sub-ps pulse duration[1] and ~10 micrometer source size[2]. This ultra short x-ray flash has great potentials in a variety of applications, such as biomedical imagines [3-4] and ultra fast probing of atomic structures [5]. It is also developed as a novel backlighter for the pulsed radiography of high energy density physics [6-7]. The Kα emission is excited in the dense target by the fast electrons generated during laser plasma collective interaction. Previous works have presented the detailed studies on the Kα emission with both non-relativistic [8] and relativistic [9] lasers. The high conversion efficiency (ηk) of laser to Kα emission is an important subject in the research for the purpose of applications. The high conversion efficiency of laser to fast electrons and appropriate electron spectra are essential in achieve this goal. The solid targets with nano structure surface have been proved to be effective in enhancing the laser absorption and the x-ray production in the moderate laser intensity. For the high laser intensity, the simulations[10] show the similar enhancement. However, the inherent prepulse of short pulse laser may modify the surface structure before the main pulse impinges on the target. There [11]is very few detailed study on the evolution of the nano-structured target under the influence of prepulse of intense femtosecond laser and its consequences on the Kα production. We