The Imaging Plate is a flexible electron detector, where an active layer of tiny crystals locally store high energetic radiation. The storage crystals are made from doted barium fluoro-bromide embedded in some blue colored resin. The electron irradiation excites the crystals in their luminescence center to a semi-stable state. The image information, formed by this excitation is stable for many hours and decays within days. By an illumination with red laser light, the crystals are excited again and stimulated to release the stored information as blue luminescence signal. The amount of blue light released depends on the first exitation with
electrons and is a direct measure of the electron dose. As this is a physical process it is fully reversible without degradation, so the Imaging Plate can be reused many times. By exposing to white light for a period of 10 to 15 minutes gradually all excitation is released and the plate is ready to be exposed again. The active layer is protected by a thin polymer layer on top. It is supported by a polymer layer and a thin metal (antimagnetic) base that gives its mechanical stability. (see figure top right)
As the excitation is stored within the crystal luminescence centers the number of available storage cells is virtually unlimited. For this reason the plate is not saturated in a TEM. Only the readout device limits the dynamic range. The electron enters the plate and deposits its energy by exciting a large number of crystal centers. The lateral electron scattering is limited to a few micron so the information is highly localized. The blue color of the resin absorbs the red laser light while perfectly transmitting the blue luminescence signal so lateral scattering of the readout light is greatly reduced.
These features make the Imaging Plate an ideal electron detector:
- High Sensitivity as one electron produces a number of photons. So virtually every single electron can be detected.
- High dynamic range as there is no saturation.
- Sharp Images as the information is highly localized (Low crosstalk)
- Large detection area.