[time-nuts] Laser Temperature System

[WB6BNQ]

   WAS Re: [time-nuts] Restoring GR 1120-AB Frequency Standard

   Mike,

   I fail to see how you would apply the laser interferometer system to
   the measurement of temperature.  At least as a viable means of
   temperature control to any reasonable degree.

   At the Navy's Primary Standards Lab, here in San Diego, there is a very
   complete laser interferometer measurement system.  It is housed in its
   own room that is "completely" controlled for environmental conditions,
   i.e., temperature, humidity, air filtration, etc.  The actual laser
   platform is a huge, highly machined micro-flat granite table of
   considerable weight mounted to a fine grain concrete pillar that goes
   down to the bedrock, some 30 feet below, and is completely separate
   from the rest of the building's foundation.

   When the operator enters this laser room, it takes a little over 30
   minutes for his body heat to be stabilized into the matrix of the rooms
   environment before any real measurements can be made.  Even though this
   granite table is, like in the neighborhood of, around 2000 lb., laying
   a standard U.S. Navy glass coffee cup (empty) on the very, very corner
   of the granite will deform the light beam quite visually.

   My reason for the above description is to point out the scale of the
   installation, the sensitivities and the problematic issues one would
   have in trying to control temperature sans everything else changing.  I
   suppose it can be reduced in size, but then doing so also reduces the
   sensitivity of the system.  Did I mention that the granite table is 3
   feet square ?  That allows for folded beams to increase the length for
   the needed sensitivity.

   Now equate all of the above to a small oven in an instrument.  Not
   likely possible.

   Bill....WB6BNQ

   Mike Monett wrote:

       Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:

       >  Max

       > A capacitance  bridge  using  a transformer would  be  a  lot
     more
       > stable than merely using the capacitance to vary the  frequency
     of
       > an LC oscillator.

       > The advantage of a capacitive sensing technique over a  light
     beam
       > is that it has much simpler and potentially more stable
     mechanical
       > system than when a the mercury colum interrupts a light beam.

       > Unless of course on has the Mercury column move a moire grating
     or
       > similar setup  such  as  making the top of  the  mercury  column
     a
       > reflector in an interferometer system.

       >  Bruce

       Very clever! According to this web page, interferometry could give
     a
       resolution of 0.15 nm, or close to the radius of a silver atom:

       [1]http://www.aerotech.com/products/engref/intexe.html

       This video  shows the basic principle in case you want to  make
     your
       own:

     [2]http://www.metacafe.com/watch/1381543/laser_interferometer_homema
     de_for_20/

       You can  see  from  the   movement   of  the  fringes  how
     sensitive
       interferometry can  be. This should  give  unprecedented
     temperature
       control, so maybe someone has already done it. A google search
     gives
       lots of hits, but it is difficult to distinguish between
     controlling
       the termperature of something, and the need for accurate  control
     of
       temperature to get stable fringes!

       Great idea!

       Regards,

       Mike Monett

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References

   1. http://www.aerotech.com/products/engref/intexe.html
   2. http://www.metacafe.com/watch/1381543/laser_interferometer_homemade_for_20/
   3. https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts