How to Build an X-ray Interferometer
An interferometer becomes necessary when the diffraction limit requires a telescope to be so large that it becomes impractical to build. Instead one builds an array of telescopes and mix the signals at the focal plane. If handled properly, a computer can reconstruct an image comparable to that which would have been attained with a telescope of diameter equal to the separation of the two telescopes. A classic case is the Very Large Array (VLA) which is an array of radio telescopes in New Mexico that together function as a giant telescope, 36km across.
In the x-ray band of the spectrum, wavelengths are much shorter, so comparable resolution can be achieved with much smaller optics. Resolution comparable to that of the Hubble Space Telescope can be achieved with an optic less than a millimeter in diameter. The very finest images taken in any band of the spectrum are long baseline radio interferometers (e.g. the VLBA), which can reach down to about .001" (100x finer than HST) on certain, select objects. This can be matched in the x-ray with a baseline of just a few inches. When baselines become challenging (i.e. tens or hundreds of meters) the x-ray interferometer will resolve a millionth of an arcsecond or better!
The required technology is, of course, challenging. X-ray optics have been poor compared to conventional, visible band optics, and to take them to this new level will require some new approaches.
Nonetheless, we have a concept that appears to be feasible with today's technology. Concept
In the next series of pages, we present our concept. It is based on the traditional multi-telescope interferometer pioneered by Michelson early in the 20th Century.
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