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Dream Cellular,
LLC's engineered substrates posses substantially lower thermal time constants than monolithic substrates.
The Thermal page illustrated three of the main
factors that influence this characteristic in our engineered
lightweight mirrors. Now we will discuss a narrower thermal aspect. |
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Most optics have
the same achilles heel: thermal gradients. These gradients can
be between the air temperature and the substrate temperature.
But they can also be termperature gradients within the substrate
itself. If your application keeps the optics at an extremely
stable temperature, <0.1C, then you can disregard the following
information as it is written based on applications where there
are changing ambient temperatures. |
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A 1C internal temperature
gradient within a monolithic/solid 16" x 2" thick Pyrex
or Borofloat 33 mirror will cause roughly 180nm of figure error
(~1/3rd wave error at 550nm). However, these gradients are virtually
eliminated through the use of our engineered cellular blanks
and forced
ventilation. The average
CTE of Dream's mirrors is 2.6-2.7x10-6/K. Pyrex and Borofloat
33 have a CTE that is 22.6% higher. This also contributes to
the far superior figure-holding performance of Dream's engineered
mirrors. |
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Thermal mass typically
increases gradients that cause degradations. These degradations
often dominate the error budget. In simple terms this can be
called mirror seeing. Dream Cellular, LLC's engineered cellular
blanks and forced ventilation can virtually eliminate mirror seeing. Dream Telescopes
& Acc., Inc. unique Filtered
Air System Technology,
in combination with Dream Cellular, LLC's engineered cellular
substrates, not only help to reduce mirror seeing and other thermal
affects, but it also fills the optical chamber with filtered,
clean air. |
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Thermal mass which
leads to temperature gradients is a factor regardless of what
a specific optic is made from. Substrates can be made from aluminum,
copper, beryllium, silicon carbide, carbon
fiber, borosilicate glass and zero-expansion glass-ceramics,
to name just a few. Certain materials are stiffer or have a higher
heat conductivity than others. Stiffness and high heat conductivity
are properties we want in an optic. |
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