Contrasting behavior of covalent and molecular carbon allotropes exposed to extreme ultraviolet and soft x-ray free-electron laser radiation

All carbon materials, e.g., amorphous carbon (a-C) coatings and C60 fullerene thin films, play an important role in short-wavelength free-electron laser (FEL) research motivated by FEL optics development and prospective nanotechnology applications. Responses of a-C and C60 layers to the extreme ultraviolet (SPring-8 Compact SASE Source in Japan) and soft x-ray (free-electron laser in Hamburg) free-electron laser radiation are investigated by Raman spectroscopy, differential interference contrast, and atomic force microscopy. A remarkable difference in the behavior of covalent (a-C) and molecular (C60) carbonaceous solids is demonstrated under these irradiation conditions. Low thresholds for ablation of a fullerene crystal (estimated to be around 0.15 eV/atom for C60 vs 0.9 eV/atom for a-C in terms of the absorbed dose) are caused by a low cohesive energy of fullerene crystals. An efficient mechanism of the removal of intact C60 molecules from the irradiated crystal due to Coulomb repulsion of fullerene-cage cation radicals formed by the ionizing radiation is revealed by a detailed modeling

In situ focus characterization by ablation technique to enable optics alignment at an XUV FEL source

In situ focus characterization is demonstrated by working at an extreme ultraviolet (XUV) freeelectronlaser source using ablation technique. Design of the instrument reported here allows reachinga few micrometres resolution along with keeping the ultrahigh vacuum conditions and ensureshigh-contrast visibility of ablative imprints on optically transparent samples, e.g., PMMA. This enableson-line monitoring of the beam profile changes and thus makes possible in situ alignment ofthe XUV focusing optics. A good agreement between focal characterizations retrieved from in situinspection of ablative imprints contours and from well-established accurate ex situ analysis with Nomarskimicroscope has been observed for a typical micro-focus experiment

Strand break formation in plasmid DNA irradiated by nanosecond XUV-laser pulses

The development of the desktop, repetitive XUV laser based on collisionally pumped transition of Ne-like Ar ions in a pinching capillary discharge [1] is of interest for numerous applications in radia-tion biophysics. Ionizing radiation induces a variety of DNA damages including single-strand breaks (SSBs), double-strand breaks (DSBs), abasic sites, modified sugar and bases. Most theoretical and ex-perimental studies have been focused on DNA strand scissions, in particular production of DNA double-strand breaks. The complexity of lesions produced in DNA by ionizing radiations is thought to depend on the amount of energy deposited at the site of each lesion. We have studied the nature of DNA damage induced directly by the pulsed 46.9 nm radiation provided by a capillary-discharge Ne-like Ar laser (CDL). Different surface doses were delivered with a repetition rate of a few Hz and an average pulse energy ~ 1 μJ. A simple model DNA molecule, i.e., dried closed-circular plasmid DNA (pBR322), was irradiated. The agarose gel electro-phoresis method was used for determination of both SSB and DSB yields

Biological Action in and out of the Water Window

This study is dealing with the difference of radiation chemical yields of single and double strand breaks induced in plasmid DNA by photons inside and outside of the soft X-ray water window, i.e., in the wavelength range from 2.28 nm to 4.88 nm. Photons were generated by various plasma sources providing nanosecond and sub-nanosecond pulses of extreme ultraviolet, soft X-ray and X-ray radiation. DNA strand breaks were determined by agarose gel electrophoresis. Higher radiation chemical yields of both single and double strand breaks were found using picosecond and nanosecond sources of extreme ultraviolet and X-ray radiation