Further development of the Xe laser plasma 11-nm radiation source – new data on laser energy absorption and spectroscopy

Absorption of the laser pulse energy in the plasma has been shown to change from 8.5% at irradiation of a gas-puff target with a beam narrow-focused onto a near-central area of the jet up to 65% at the wide defocused irradiation. An analysis of this phenomenon is based on a hypothesis that plasma density decays significantly during the 10ns laser pulse due to hydrodynamic expansion of the hot plasma. A similarity of the EUV (Extreme UltraViolet) intensity and the laser light absorption as functions of the laser beam diameter suggests a revision of the conventional idea of a strong EUV radiation self-absorption in a cold peripheral shell of the laser plasma whereas the high absorptivity of the laser radiation by the plasma looks like a major feature to gain high efficiency of an EUV source.