In a message dated 08/04/03, dyouden@......... writes:
> For information on high resolution stage interferometry go to:  
> http://www.zygo.com/
> Select semiconductor, stage position, zmi systems, and read all about it. 

Hi Dave,

       There is an excellent introductory document which will probably tell 
most folks more than they ever wanted to know about optical distance 
measurement using the wavelength of light, exactly how it is done and what 
the problems are. There are a lot of diagrams.
       This Technical Paper is in the section ZMI systems. "High-resolution, 
High-speed, Low Data Age Uncertainty, Heterodyne Displacement Measuring 
Interferometer Electronics". (149 k)    
       I can see why these systems are so expensive. The max range given in 
metres is very impressive. Fortunately, we only need to measure distances of 
maybe 1 mm for seismometers and less for feedback systems, so capacitative 
detectors can cope with the range and give an order of magnitude greater 
resolution. 
       However, my comment that optical systems which depend on wavelength 
need complex = expensive systems to get below 1/2 wavelenght seems to be 
accurate enough.
       Thanks Dave. I found it very instructive.

       Regards,

       Chris Chapman 
In a message dated 08/04/03, dyouden@......... writes:

For information on high res=
olution stage interferometry go to:  http://www.zygo.com/

Select semiconductor, stage position, zmi systems, and read all about it=
.. 




Hi Dave,



       There is an excellent introductory=20=
document which will probably tell most folks more than they ever wanted to k=
now about optical distance measurement using the wavelength of light, exactl=
y how it is done and what the problems are. There are a lot of diagrams.

       This Technical Paper is in the sect=
ion ZMI systems. "High-resolution, High-speed, Low Data Age=
 Uncertainty, Heterodyne Displacement Measuring Interferometer Electronics".=
 (149 k)   =20

       I can see why these sys=
tems are so expensive. The max range given in metres is very impressive. For=
tunately, we only need to measure distances of maybe 1 mm for seismometers a=
nd less for feedback systems, so capacitative detectors can cope with the ra=
nge and give an order of magnitude greater resolution.=20

       However, my comment that optical sy=
stems which depend on wavelength need complex =3D expensive systems to get b=
elow 1/2 wavelenght seems to be accurate enough.

       Thanks Dave. I found it very instru=
ctive.



       Regards,



       Chris Chapman