Evidence of plasma polarization shift of Ti He-α resonance line in high density laser produced plasmas

Abstract

A spectroscopic study of the He-α (1s21s 0 - ls2p 1p1) line emission (4749.73 eV) from high density plasma was conducted. The plasma was produced by irradiating Ti targets with intense (I ≈ 1×l019 W/cm2), 400nm wavelength high contrast, short (45fs) p-polarized laser pulses at an angle of 45°. A line shift up to 3.4±1.0 eV (1.9±0.55 mÅ) was observed in the He-α line. The line width of the resonance line at FWHM was measured to be 12.1±0.6 eV (6.7±0.35 mÅ). For comparison, we looked into the emission of the same spectral line from plasma produced by irradiating the same target with laser pulses of reduced intensities (≈1017 W/cm2): we observed a spectral shift of only 1.8±1.0 eV (0.9±0.55mÅ) and the line-width measures up to 5.8±0.25 eV (2.7±0.35 mÅ). These data provide evidence of plasma polarization shift of the Ti He-α line.