D r e a m

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.

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.
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.

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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