Soft x-ray lasers and Raman amplification in plasmas

A new 3–4 TW Ti:sapphire laser system operating at 5 Hz, 800 nm has been installed, which is capable of providing laser intensities more than 1018 W/cm2 with proper focusing optics. These high power laser pulses have been employed as the pumping pulse for optical field ionization of Li for generation of soft x-ray radiation in microcapillary plasmas. The spatio-temporal evolution of the microcapillary plasma has been studied by both hydrodynamic simulations and interferometric density measurements. A waveguiding density profile has been observed and the waveguiding of intense laser pulses in microcapillary discharges have been demonstrated. The gain generation for the n = 2–1 transition at 13.5 nm in LiIII ions was investigated in two types of plasmas. A gain length product of GL ≈ 3 and GL ≈ 7 were estimated in laser created plasmas and in discharge created plasmas, respectively. The analysis shows that waveguiding of the pumping pulses can increase the interaction length thus to improve the gain length product. Another possibility of producing high power laser pulses by Raman amplification for pumping the soft x-ray laser has been investigated. The amplification of ultrashort pulses through the Raman process in plasmas has been demonstrated for the first time. Further investigations with broadband seed pulses produced by an optical parametric oscillator show consistency with the theory and the observed Raman resonance is in agreement with the plasma density measurements.