Ghost-Imaging Technology Could Have Satellite Application Published Sept. 19, 2008 By Maria Callier AFOSR ARLINGTON, Va. -- AFRL-funded investigators from the University of Maryland, Baltimore Campus are conducting research under the name of "ghost imaging," wherein a visual image of an object is created by means of light that has never interacted with the object. The emerging technology may eventually result in the more versatile use of field sensors, and could have space utility as well. It was in 1995 that the University of Maryland's Professor Yanhua Shih initiated what would become known as ghost-imaging research. The focus of Dr. Shih's effort was the use of entangled photons. During his experimentation, one photon passed through stenciled patterns in a mask to trigger a detector, while another photon was captured by a second detector. Surprisingly, an image of the pattern appeared between the two detectors, a phenomenon the physics community promptly labeled "ghost imaging." In an article entitled "Reflection of a Ghost," published in the April 2008 edition of Physical Review, fellow researcher Dr. Keith Deacon alludes to the promise that ghost imaging holds for future application to satellite technology. Specifically, ghost imaging may enable satellites to be equipped with a detector that, when coupled with a second camera, could take images of the sun. Further, this same type of configuration could generate ghost images of the earth's surface during even the most inclement (i.e., obstructive) atmospheric conditions. Dr. Shih worked with two cohorts from the US Army Research Laboratory, Drs. Ron Meyers and Keith Deacon, in producing ghost images using thermal light. The three scientists combined signals from two detectors--one of which that collected light reflected from a toy soldier and the other that took a digital picture of the light source used for the experiment. The mechanics of ghost imaging are similar, though not identical, to those involved in flash photography. In snapping a flash-lit photo using a normal camera, the image forms as a result of photons emitted from the flash, bounced off the object, and focused through the camera lens onto photoreactive film or a charge-coupled array. Conversely, ghost images do not form as a result of light (photons) hitting an object and bouncing back. Instead, the camera captures photons emitted from sources of light that did not hit the object and paired (through a quantum effect) with photons from light that did. The ghost image begins to appear once the camera has recorded approximately 1,000 photon pairs in this manner.