The Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) will employ a wide variety of spectral filtration components including narrow band, medium band, wide band, and far ultraviolet (FUV) long pass filters, spatially-variable filters (ramp filters), VIS/IR polarizers, NUV polarizers, FUV prisms, and a grism. These components are spread across ACS's Wide Field, High Resolution, and Solar Blind channels which provide diffraction-limited imaging of astronomical targets using aberration-correcting optics which remove most aberrations from HST's Optical Telescope Assembly (OTA). In order for ACS to be truly advanced, these filters must push the state-of-the-art in performance in a number of key areas at the same time. Important requirements which these filters must meet include outstanding transmitted wavefront, high transmittance, uniform transmittance across each filter, spectrally structure-free bandpasses, exceptionally high out of band rejection, and a high degree of parfocality. These constitute a very stringent set of requirements indeed, especially for filters which are up to 90 mm in diameter. The development of optical metrology stations used to demonstrate that each ACS filter will meet its design specifications is discussed. Of particular note are specially-designed spectral transmissometers and interferometers.
Keywords: bandpass filters, transmissometry, index of refraction, focal shift, transmitted wavefront
Brief Biography, Principal Author:
Presently: Douglas B. Leviton, Optical Engineer in the Optics Branch at Goddard Space Flight Center, Greenbelt, MD; Optics lead engineer for development of the HST ACS filter set; Research areas include development of test methods for flight optics, new optical fabrication technology, and new technology optical encoders; B.S. Physics, Emory University, Atlanta, GA, 1981; M.S. Physics, Georgia Institute of Technology, Atlanta, GA, 1983
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