SNOM characterization of micro-radiographs stored in lithium fluoride thin films

Nowadays the possibility to obtain micro-radiographs is limited in resolution by the detection properties of the used technique. Here we show a new method to create and observe micro-radiographs. A thin film of Lithium Fluoride works as image detector, storing the micro-radiograph obtained exposing biological material to Extreme Ultra-Violet and soft X-ray radiations. To read the stored image, collecting the optically stimulated luminescence of the active color centers produced by the X-rays, a Scanning Near-Field Optical Microscope (SNOM) is used, for its peculiarity to overcome the diffraction limit, showing details smaller than the wavelength of the collected light. The samples were illuminated with 458 nm laser light and an uncoated tapered optical fiber was collecting the fluorescent signal emitted by the Lithium Fluoride color centers. The SNOM images of these micro-radiographs stored in Lithium Fluoride films showed an optical resolution of 50 nm, corresponding to lambda/12, where lambda is the wavelength of the collected light.