Window for vacuum telescopes: Review of problem areas
Abstract
The mechanical properties of a large disk of BK7 glass, and the optical effects of the pressure load and thermal environment are discussed. A 150 cm diameter free window is feasible using BK7. For a maximum bending stress not exceeding 125 kp/sq cm, thickness should be greater than 7.7 cm. Active temperature control of the cell is required to overcome thermal nonuniformities between center and rim and to eliminate birefringence due to thermally induced stress. If multiwindow apertures are used, temperature within the assembly must be constant within 0.1K in the coherent case. The wedge angle of the elements should equal twice the resolution angle for incoherent use. The thickness should equal 0.2 lambda, the amount corresponding to a constant wedge angle for a coherent case window.
- Publication:
-
Large European Solar Telescope
- Pub Date:
- April 1982
- Bibcode:
- 1982lest.rept..199M
- Keywords:
-
- Reflecting Telescopes;
- Structural Design Criteria;
- Vacuum Tubes;
- Windows (Apertures);
- Active Control;
- Bending Moments;
- Birefringence;
- Mechanical Properties;
- Optical Properties;
- Temperature Effects;
- Thermal Stresses;
- Thickness;
- Astronomy