The discovery of x rays by Röntgen in 1895 [1] was widely noticed, mainly due to the large interest in images of the interior of the human body. They were simple shadowgraphs, similar to the contact copy of a photographic negative, and were impressive, because x rays could penetrate tissue without scattering. Such shadowgraphs still represent the main application of x rays today. The shadowgraph technique has been extended to resolve fine features in microscopy; x-ray lithography is an application of this technique, which promises the fabrication of the electronic chips of the future.

Röntgen tried immediately to deflect, refract, or reflect x rays, in order to explore the possibility of imaging devices. He did not observe any deflection and stated in his first note that the refractive index of all materials for x rays was very close to that of air or vacuum with a deviation of less than 0.05. He also checked if x rays could be reflected, by comparing the transmission of blocks of various materials in powder form to that of solid blocks. He found no difference in the transmission. Because multiple reflections from the powder surfaces would have enhanced scattering, like sugar or snow does for visible light, he concluded that the reflectivity had to be extremely low. He summarized that x rays could not be deflected by refraction, reflection, and scattering, and that lenses and mirrors for x rays were not possible.

The discovery of x-ray diffraction from crystals [2] provided for the first time a method to deflect x rays by large angles.

© 1994 Society of Photo-Optical Instrumentation Engineers

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