Ref: Laser Metrology/ Encoders

So not much chance of an el-cheapo interferometer type thing, it's super
accurate lab type stuff all the way.
Thanks very much for the reply, it cleared up my confusion. I was thinking of
waves as the surface of the water going up and down which seems like a bit of
a misconception regarding light.....and there was some quantum too.
So all in all the 2 beams are necessary as the phasing of the beams is what
makes the wavelength measurable.
And a laser pointer isn't really a usable source as the wavelengths are
messed up (not sure if its the lengths or the alignment or if I'm barking up
the wrong tree altogether).
Besides all that, something would be needed to count all the phases and there
are around 4 million of them a meter if the sensor is beside the laser and
the beam is being reflected back from whatever is being measured. Actually,
that bit isn't too bad and 4000 divisions per mm is a usefull number.
Could you give me a better idea on laser pointers or cd drive lasers as a
light source? The concept doesn't seem to tricky but something to hold it all
together on a vibrating machine looks difficult, it seems like it would need
3 or more side by side to tell which direction the thing is moving. Oh,
and 'if you need to ask, you can't afford it' prisms, but it would be nice
even to see it working on a steady surface.
Looking over that, I'm assuming the phases stay where they are if the
distance stays the same and aren't going in and out at some speed related to
the speed of light. is that right?
Thanks again, eying up my troublesome cd drive in anticipation :)
cheers

--
We're only in it for the volume.
-- Black Sabbath