Conversion efficiency and spectral broadening of the K-α line emitted from planar titanium targets irradiated with ultra-short laser pulses of high intensity

Abstract

A study of the conversion efficiency and line shape of the K-α x-ray line radiation from a planar titanium target irradiated by an ultra-short laser pulse is performed. The conversion efficiency and spectral broadening are studied as a function of laser intensity (5 × 1016–1018 W cm−2), laser pulse duration (45 fs–800 fs), and laser fluence (2 × 103–4.2 × 104 J cm−2). The K-α1 line (4510 eV) is observed to be broadened (up to ∼9 eV), predominantly towards the higher energy side and strongly depends on the laser fluence rather than on laser intensity. The reason for the spectral broadening is attributed to K-α emission in warm dense plasma. The role of hot electrons and direct laser heating on spectral broadening is outlined. In addition to this, our observations indicates that the presence of pre-plasma strongly contribute to the observed broadening through the inner-shell transitions in multiply charged titanium ions in the pre-plasma. The appropriate laser irradiation parameters to achieve high conversion efficiency and minimum spectral width of the K-α radiation are identified. The study is important, since the control of the spectral profile is of general interest for diffraction or scattering experiments in view of its potential in increasing temporal resolution.