Scanning near-field optical microscopy images of microradiographs stored in lithium fluoride films with an optical resolution of λ∕12

Here we show a new, simple method to observe soft x-ray microradiographs of biological material. A thin film of lithium fluoride (LiF) works as image detector, storing the microradiograph obtained exposing biological samples to extreme ultraviolet and soft x-ray radiations. To read the stored image, collecting the optically stimulated visible luminescence emitted by the LiF active color centers locally produced by the x rays, a scanning near-field optical microscope is used with an optical aperture of 50nm, i.e., λ∕12, where λ is the wavelength of the collected photoluminescence.