Absolute extreme ultraviolet yield from femtosecond-laser-excited Xe clusters

Large Xe clusters ${(10\mathrm{}}^5–{10}^6$ atoms per cluster) have been irradiated with ultrashort (50 fs) and high-intensity $(\sim 2\times {10}^{18}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2)$ pulses from a Ti:sapphire multi-TW laser at 800 nm wavelength. Scaling and absolute yield measurements of extreme ultraviolet (EUV) emission in a wavelength range between 7 and 15 nm in combination with cluster target characterization have been used for yield optimization. Maximum emission as a function of the backing pressure and a spatial emission anisotropy covering a factor of two at optimized yields is discussed with a simple model of the source geometry and EUV-radiation absorption. Circularly polarized laser light instead of linear polarization results in a factor of 2.5 higher emission in the 11 to 15 nm wavelength range. This indicates the initial influence of optical-field ionization for the interaction parameter range used and contrasts to collisional heating that seems to influence preferentially higher ionization. Absolute emission efficiency at 13.4 nm of up to 0.5% in 2π sr and 2.2% bandwidth has been obtained.