Michelson interferometer-Coherence required?
Michelson interferometer-Coherence required?
(OP)
Good day. I'm using a Michelson interferometer constructed on a cushioned optical table to measure deflections of small, pressurized membranes (2mm square and a few micrometers thick). We are currently using a small He-Ne for the light source, but would like to switch to a pulsed YAG (Continuum SureLite with the power significantly cut down) so that we can capture essentially instantaneous interferograms of the membrane being flexed dynamically (up to about 1kHz). Here's the problem: The (large and difficult to move) YAG is in one room, and my experiment is in the next room. So my professor says "no problem, rig up a series of mirrors to reflect the light from one room into the other and use it in your experiment". Riiigght, I say, but the laser light needs to be coherent for effective interferometry, and I question if the coherence will be maintained after reflection off 6 mirrors (each having lambda/10 flatness at best) and travelling a distance of about 60 feet. She says to try it anyway.
Who's crazy here? Do I have a prayer of generating clear interference patterns with this arrangement? Thanks!
Who's crazy here? Do I have a prayer of generating clear interference patterns with this arrangement? Thanks!





RE: Michelson interferometer-Coherence required?
If it works send us a pic - eatmore.toast@physics.org
Vik
RE: Michelson interferometer-Coherence required?
You are right: the YAG has a TERRIBLE wavefront; pulsed lasers and especially solid state ones have this behaviour.
That's why u use He-Ne in school for Michelson: gas laser, plus low power = nice wavefrnt profile, good for interferometry.
Your adviser wouldn't know anything about optics, would she?
Cheers
RE: Michelson interferometer-Coherence required?
You may be able to achieve what you want without the extra trouble. Coherence won't be a problem with the YAG, but there are a lot of other factors in trying to pipe the beam over that could distort your results.
Bob
RE: Michelson interferometer-Coherence required?
interferometer.
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