Photorefractive effects that are generated or affected by X-rays may allow to design an X-ray imaging system with high spatial resolution. Different concepts are studied: (1) The X-ray image yields a photoconductivity pattern. An external electric field is applied and hence a space-charge field builds up that is a replica of the original X-ray image. Through the electrooptic effect a spatial modulation of the birefringence occurs. This birefringence pattern can be detected directly with visible light, a polarizer, an analyzer, and a CCD camera. (2) An elementary holographic grating is recorded. The X-rays yield again a photoconductivity pattern and erase the hologram inhomogeneously. The diffracted light now bears the X-ray image. Both approaches are are studied with lithium-niobate crystals (LiNbO3). This material is found to be highly resistant against permanent damage caused by X-rays. Undesired photochromic effects are also found to be very weak. First experimental investigations of the two camera concepts are presented, and the principal advantages and disadvantages of such imaging systems are discussed. Besides high spatial resolution, that is limited in principle just by the wavelength of the probe light, other advantages are the time-integrative character of such a detector togehter with full reversibility.
© 2001 Optical Society of AmericaPDF Article
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