The high transparency of carbon-containing materials in the spectral region of "carbon window" (lambda approximately 4.5-5nm) introduces new opportunities for various soft X-ray microscopy applications. The development of efficient multilayer coated X-ray optics operating at the wavelengths of about 4.5nm has stimulated a series of our imaging experiments to study thick biological and synthetic objects. Our experimental set-up consisted of a laser plasma X-ray source generated with the 2nd harmonics of Nd-glass laser, scandium-based thin-film filters, Co/C multilayer mirror and X-ray film UF-4. All soft X-ray images were produced with a single nanosecond exposure and demonstrated appropriate absorption contrast and detector-limited spatial resolution. A special attention was paid to the 3D imaging of thick low-density foam materials to be used in design of laser fusion targets.

The paper deals with the recent results of the experiments on soft X-ray imaging of various carbon-containing objects: biological samples, artificial carbon fibres, graphite slices, etc. The working wavelength was chosen to be 4.5 nm due to high penetration ability of these soft X-rays in the carbon materials. The experimental set-up included: laser plasma Xray source (generated with the 2nd harmonics of Nd:YAG laser), scandium-based thin-film filter and highly reflective spherical multilayer mirror. The Co/C multilayer's reflectivity was measured to be about 15 % at normal incidence that was high enough to produce soft X-ray images using single nanosecond exposure. The work demonstrates a possibility to produce high contrast images outside "water window" region for study of relatively thick (tens of microns) unstained samples that may lead to new fields of applications of the soft x-ray microscopy

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