Speckle Interferometry Interferometrie below 10µm

From: luck80@xxxxxxxxx
Date: 27 Aug 2006 02:27:39 -0700

Hi all...

I'm trying to measure object forms with speckle interferometry and two
wavelengths

LAMBDA_synth = (lambda_1*lambda_2) / (2*|lambda_1-lambda_2|)

I'm using some roughness comparators with Ra=0.4µm.
As long as I work with a LAMBDA_synth greater than 100µm everything
works fine.
But as soon I get arround 25µm, I measure some OPD caused by the
lenses.
And below 5µm there are stripes at all anymore.

Any ideas why I can't measure below 5 µm?

.

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