The Wilson Interferometer.
in [Relativity]
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From: Uncle Al on 20 Oct 2009 18:38 Henry Wilson DSc wrote: > > Would this work? > > I am wondering if an interferometer of the basic Michelson type would produce > fringes if the crossbeam was removed altogether. > > (use fixed pitch font) > > S------->-----------/----------<---------M > > O > > If the source light is truly coherent I see no reason why the returning light > should not interfere with the direct beam and form rings on the 45 mirror, > which would be seen by the observer O. > > If anyone here understands interferometers they will know that the eyepiece or > camera focusses on the 45 mirror. I say THAT is where the fringes form. So what > difference does a crossbeam make? arXiv.org:0706.2031 arxiv.org:0801.0287 -- Uncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2
From: Jerry on 20 Oct 2009 19:33 On Oct 20, 5:33 pm, HW@..(Henry Wilson DSc). wrote: > Would this work? > > I am wondering if an interferometer of the basic Michelson type would produce > fringes if the crossbeam was removed altogether. > > (use fixed pitch font) > > S------->-----------/----------<---------M > > O > > If the source light is truly coherent I see no reason why the returning light > should not interfere with the direct beam and form rings on the 45 mirror, > which would be seen by the observer O. > > If anyone here understands interferometers they will know that the eyepiece or > camera focusses on the 45 mirror. I say THAT is where the fringes form. So what > difference does a crossbeam make? (sigh) Work it out, idiot. Without a crossbeam, classical wave theory (i.e. aether-based) does not predict velocity-dependent fringe shifts. Jerry
From: Tom Roberts on 20 Oct 2009 20:22 Henry Wilson DSc wrote: > S------->-----------/----------<---------M Look up Wiener fringes. > If anyone here understands interferometers they will know that the eyepiece or > camera focusses on the 45 mirror. Not true. In a Michelson interferometer the eyepiece is focused at infinity. To understand why requires an analysis of the various light rays. Tom Roberts
From: Tom Roberts on 20 Oct 2009 23:04 Henry Wilson DSc wrote: > [about an interferometer] > Well, without dispersion there would be no path length differences and no > fringe pattern. Not true. How do you think interferometers in vacuum work? You must ANALYZE the different light rays, not just make unfounded assertions. Hint: every light source has a nonzero divergence, and every eyeball has a nonzero radius. Tom Roberts
From: Jonah Thomas on 21 Oct 2009 00:14
HW@..(Henry Wilson DSc). wrote: > Well, without dispersion there would be no path length differences and > no fringe pattern. > > Try this arrangement then, which is what I really meant: > > S------->----------/\----------<---------M > > > > > O > > Now the observer receives light from both the source and the mirror > via the two half silvered mirrors. > If the source beam is coherent and parallel, why shouldn't > interference occur. The fact that the path lengths are different > shouldn't matter. http://skullsinthestars.com/2008/09/03/optics-basics-coherence/ * well-stabilized laser: coherence time, 10^-4 seconds, coherence length = 30 km * filtered thermal light: coherence time, 10^-8 seconds, coherence length = 3 m 3 meters is enough to do a lot. But some lasers have a shorter coherence length than that. > I'm asking this because of claims here that two similar but > independent laser beams can interfere. http://skullsinthestars.com/2008/09/12/interference-between-different-photons-never-occurs-not-1963/ "Coherence" is basicly a measure of how well the light interferes. Over time and distance laser light from a single source interferes with itself less well. To get laser light from two sources to interfere you have to tune them carefully, and presumably the better that's done the longer they'll interfere. This link describes the first experiment that showed interference between two different lasers. The interference was weak enough that it had to be detected. "Thanks to the weakness of the fringe pattern and the poor photo reproduction of the era, the photograph is a bit of a Rorschach test of a scientific result. the microphotometer tracing below it, though, is unambiguous: the fields from the two independent lasers produce a fringe pattern!" You might be interested in another experiment described in the same link. They did low-intensity interference studies, and found that light from the two different lasers interfered even when almost always one photon would have been absorbed before the next photon from either laser arrived. That is, the two lasers were doing interference but it was not two photons interfering. It was something that does not make sense. |