High energy-resolution measurements of x-ray into ultraviolet parametric down-conversion with an x-ray tube source

We describe high energy-resolution measurements of parametric down-conversion of x-rays into ultraviolet radiation using a standard laboratory x-ray tube source with very minor modifications. We measure the effect in diamond and in lithium fluoride crystals in the ultraviolet range from 30 eV to 65 eV. We show that the effect depends strongly on the fluorine L_I edge at 37 eV and on the K edge of the lithium at 55 eV. The comparison with theory reveals that the classical model that was previously used for the description of the effect agrees with the experimental results in diamond. However, the discrepancies of the model with the experimental results in lithium fluoride are prominent.