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In article ,
Earl Colby Pottinger wrote: People are still struggling to make imaging interferometry work well at distances of a hundred *meters* with both telescopes resting on solid rock. Henry, correct me if I am wrong. But I thought with present day computers you don't need to hold the distance steady between the scopes. Rather you needed to know the distance to a fraction of a wavelenght between the scopes at the time the signals are recorded. The key requirement is that you need to be able to measure the relative phase of the photons arriving at the two scopes. There are two ways you can do that, in principle. One way is to bring those photons together so they interfere, and measure the results of the interference. That gives you a direct readout of the relative phase. The length of the optical path that brings the photons together must be stable -- or at least continuously measurable -- to a fraction of a wavelength, because any change in its length adds spurious phase differences between the photons. The other thing you can do is *record* the phases of the photons at each scope, along with very precise time references, so you can compare them later at your leisure, essentially simulating the interference in the computer. The problem is, we have no way to do that for *light*. The required speed of the phase measurement and recording system is four or five orders of magnitude higher than that for radio. Opps, just realized with long radiowaves even the phase shift can be measured - if you need the phase of visible light to be recorded at both scopes at the same time I don't think we have reach that tech yet. Exactly. -- "Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | |
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