Enhancement of keV x-ray emission in laser-produced plasmas by a weak prepulse laser

Abstract
X-ray conversion efficiency in a 0.53-μm laser-produced copper plasma is studied in the 1.5–5.0 keV range as a function of laser pulse duration (τL) with a laser intensity of 1×1014 W/cm2. The efficiency increases as τ1.3L at pulse lengths of less than 400 ps. For a 200-ps pulse duration, an enhancement of the conversion efficiency is observed with the use of a prepulse. The efficiency is found to be proportional to the scale length of a preformed plasma. Enhancement of a factor 3 is observed for the shots with a prepulse.