Vacuum window optical power induced by temperature gradients

David R. Hearn

doi:10.1117/12.363523

24 September 1999 Vacuum window optical power induced by temperature gradients

David R. Hearn

Proceedings Volume 3750, Earth Observing Systems IV; (1999) https://doi.org/10.1117/12.363523
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1999, Denver, CO, United States

Abstract

The Advanced Land Imager (ALI) of the EO-1 satellite has been calibrated under its normal operating conditions in a thermal vacuum chamber. The optical equipment for the calibrations had to be placed outside the chamber. The effects on the calibrating beam of the vacuum chamber window are described here. Since the instrument senses the reflected solar spectrum, the existing fused-silica window was found to have adequate spectral transmission properties. It also was measured to cause little wavefront error by itself. When the chamber is under vacuum, and the interior cold shroud is cooled to approximately 100 K, the window develops significant optical power. This is a result of radiational cooling of the window, coupled with change of its index of refraction with temperature. Such an effect seriously compromises the spatial calibrations of the instrument, particularly MTF measurements. This effect was overcome in two ways: A heating plate placed outside the window was used to alter the temperature distribution until its effect on the wavefront was negligible. The more practical solution was to measure the window power with an interferometer, and compensate for it by shifting the target reticle of the collimator.

Citation Download Citation

David R. Hearn "Vacuum window optical power induced by temperature gradients", Proc. SPIE 3750, Earth Observing Systems IV, (24 September 1999); https://doi.org/10.1117/12.363523

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available