Femtosecond-Laser-Driven Cluster-Based Plasma Source for High-Resolution Ionography

The intense isotropic source of multicharged ions, with energy above 300 keV, was produced by femtosecond Ti:Sa laser pulses irradiation (intensity of ∼4x1017 W/cm2) of the He and CO2 gases mixture expanded in supersonic jet. High contrast ionography images have been obtained for 2000 dpi metal mesh, 1 μm polypropylene and 100 nm Zr foils, as well as for different biological objects. Images were recorded on 1 mm thick CR-39 ion detector placed in contact with back surface of the imaged samples, at the distances 140-160 mm from the plasma source. The obtained spatial resolution of the image was ∼600 nm. A 100 nm object thickness difference was resolved very well for both Zr and polymer foils. The multicharged ion energy for Carbon and Oxygen ions passing through the 1 μm polypropylene foil is estimated to give the energy of more than 300 keV. An almost equal number of ions were measured with total number of about 108 per shot at a different direction from plasma source. Easy production of different sub-MeV ions in wide space angle, recognizes femtosecond-laser-driven-cluster-based plasma as a well-suited bright source for novel type of submicron ionography to image different media, including nanofoils, membranes, and other low-contrast objects.