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Dream's engineered mirrors
posses substantially
lower thermal time
constants compared to monolithic (solid) mirrors. 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 occur when
there is a difference between the air temperature and the mirror's
temperature. But they can also be temperature gradients within
the mirror itself. If your application keeps the optics at an
extremely stable temperature, <0.1°C, 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 1°C internal temperature
gradient within a monolithic/solid 16" x 2" thick borosilicate
glass mirror will cause roughly 180nm of figure distortion (~1/3rd
wave error at 550nm). However, these gradients are virtually
eliminated through the use of our engineered lightweight mirrors
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. |
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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's engineered lightweight mirrors and forced ventilation can virtually eliminate mirror seeing. Dream's unique
Filtered
Air System Technology,
in combination with Dream's engineered lightweight mirrors, 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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