Enhancement of soft X-ray emission from fs laser plasma by using mixture of molecule and atomic gases as cluster jet targets and its application for nanostructure imaging

Submicron scale clusters, produced by mixture of molecular (CO₂) and atomic (He) gases expanding from the specifically designed super-sonic nozzle, have been irradiated by femtosecond laser pulses in order to build up a bright debris-free soft X-ray source. Spectroscopy measurements showed that X-ray flux in the strongest oxygen spectral lines (He_β at 665.7 eV and L_yα at 653.7 eV) produced by the plasma from gas mixture clusters is 2-8 times larger than in the case of using pure CO₂ or N₂O clusters as targets and reaches values about 2.8x10¹⁰ ph/(sr · pulse). Lines intensity and spatial dimension were measured from two observation point - along and perpendicular to the laser beam propagation directions. Images of 100 nm thick Mo foils in a wide field of view (cm² scale) with high spatial resolution (700 nm) were obtained using LiF crystals as soft X-ray imaging detectors. Agreement between calculated and measured intensity of the image fragment which illustrates overlapping of Mo foil layers confirms accuracy of the plasma parameters measurements.