  X-ray imaging allows for a non-invasive image of the internal structure of an
object. The most common form of X-ray imaging, projectional radiography, is
simply a projection or "shadow" of the object rather than a point-to-point
image possible with a lens. This technique fails to take advantage of the
resolving capabilities of short-wavelength X rays. Various X-ray microscopes,
typically operating with soft X rays (< 10 keV), use focusing X-ray optics to
obtain higher resolution images of the internal structure of an object. Due to
the short focal length of focusing X-ray optics, it becomes difficult to focus
on the internal structure of larger objects in such a way to provide
significant magnification to be resolvable. Here we present an imaging
mechanism that utilizes two-photon X-ray ghost imaging to produce a true
point-to-point image of the internal structure of an object, with the potential
to introduce focusing X-ray optics or a scintillator-lens pairing to produce a
magnified secondary ghost image. The focusing X-ray optics would image the
primary ghost image (which has no physical structure to it) allowing the
imaging of internal structures deeper than a standard X-ray microscope would
allow. In principle, once some experimental barriers are overcome, this X-ray
"ghost microscope" may achieve nanometer spatial resolution and open up new
capabilities that would be of interest to the fields of physics, material
science, and medical imaging.
