I have had much success with a microscope-based laser interferometer. It may be
overkill for what you need, but if not I've attached a GIF file of the
experimental setup. I have measured deflections with an accuracy of
approximately 1 nm with phase-only/mostly micromirrors. For cantilever devices,
I have experienced a limiting factor depending on the range of deflection. This
setup produces a continuous set of data depicting localized deflection vs.
device actuation.

Another possibility is a WYCO (sp?) interferometer system which does the same
thing over the entire surface of the device. I have heard of varying accuracy,
so I'm not able to compare the two systems. I have only seen one at MIT and I
was informed that it was not as accurate.

If you have further questions about the setup, let me know...

M. Adrian Michalicek
[email protected]