An interferometric approach to the measurement of the diffuse light from optical surfaces and systems
Images of astronomical sources are affected by stray light produced in the Earth atmosphere and in the telescope optics. The stray light causes a cross-talk phenomenon between intensity and spectral distribution at the image plane. As far as telescope stray light is concerned, its amount largely depends on the finish grade of telescope optics. Available techniques to measure the finish grade of optical components include the accurate profilometry of the surfaces and the usage of star simulators. Referring to digital phase-shift interferometry, a novel technique is presented where the diffuse light is evaluated after speckle field statistics. This technique may be easily used to give an a priori estimate of telescope stray light. At the exit pupil of a measuring interferometer, partially developed speckle patterns are produced by reflection or transmission of the probe beam on the optics under test. The standard deviation of the field distribution is shown to account for the stray light at the image plane by Fourier transform. The technique is demonstrated on a set of selected samples of different surface finish. Results prove the approach suited to qualify single optical components and to properly model their imaging properties. The application of the speckle technique to functioning reflecting telescopes is also discussed.
Astronomy and Astrophysics
- Pub Date:
- September 1993
- stray light - instrumental scattering