Lpc2000

I'm going back in time here to a reflectometer system I was involved 
with from '85 to '89. It used both reflected signal strength and phase 
shift to measure the thickness of deposition layers down to Angstroms. 
Absloute distance is measured in a similar fashion using CW radar, by 
modulation of the transmitted frequency, but I'm not into lasers enough 
to know if that is a comon technique.

Al

rtstofer wrote:

>--- In lpc2000@yahoogroups.com, Onestone <onestone@...> wrote:
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>>I thought the commercial systems used phase shift to determine distance?
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>>Al
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>I believe the phase shift approach is used to measure distance moved,
>not absolute position.  Laser interferometry (counting interference
>fringes or counting wave nulls) has been around for many years.  We
>used it to calibrate the optical encoders on numerical control
>equipment way back in the late '60s.
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>Richard
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>Yahoo! Groups Links
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