Hi Gareth,


Perhaps you can place a small force (in a known direction) on the sample as
you observe the way the fringes shift. This will easily tell you the
direction of the height variation (probably a much simpler method than
trying to compare the phases of reflected light -- especially because
anything  you try to do to compare the phases would require a measurement
way outside of the coherence length of a reflection!)

Just a thought from your friendly neighborhood Japanese translator...

Warren

_________
Dr. Warren Smith
Japanese-English Translation Services
Japanese-English Technical Services
1-800-884-5387

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