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Filters

Filters. N. Geis MPE. PACS Filter Scheme. Filter scheme with 5 or 6 filters in series in each instrument channel to provide sufficient out-of-band suppression Specified in-band transmission > 80 % for long-pass and dichroic filters ~ 80 % for band-pass filters

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Filters

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  1. Filters N. Geis MPE Filters

  2. PACS Filter Scheme • Filter scheme with 5 or 6 filters in series in each instrument channel to provide sufficient out-of-band suppression • Specified in-band transmission • > 80 % for long-pass and dichroic filters • ~ 80 % for band-pass filters • > 40 % for each filter stack • ~ 50 % expected • Out-of band suppression ~ 99% per filter Filters

  3. Example Filter Chain: Long-Wavelength Photometer Dichroic beam splitter130.µm Long-pass edge filters 52.µm 110.µm 125.µm Short-pass edge filter 210.µm Filters

  4. Examples of QMW filters Filter Types Examples of QMW filters This style used in Bolometers and Ge:Ga detectors This style used everywhere else Filters

  5. Filter Curves - Typical Blocking Filters Filters

  6. Filter Curves - Dichroic Spectrometer Shortest wavelength band close to edge of workable dichroic range Filters

  7. Filter Curves - Dichroic Photometer Shortest wavelength band badly affected by resonant effect --> fundamental problem Filters

  8. PACS Filter Status • 18 of 26 (single) filters for CQM received • Most filters exceed in-band design specs • initial surface cleanliness problem solved • 2 bolometer filters rejected for FM/FS but to be “used as is” for CQM • Embedded contamination (large items) shadow bolometers significantly (see pictures next page) Filters

  9. Defects not at real position 1 “streak” “insect” placed at center “Fibre blob” Blue bolometer array red bolometer Vignetting from Contamination in 2 Bolometer Filters acceptable: few % unacceptable: 35 % Filters

  10. PACS Filter Status • Dichroics are worse than expected: • reflected wavelength range less extended than prediction (resonant damping at 1st overtone of edge wavelength) • suppression of long wavelength in reflection only 95% on average==> probably a principal problem of QMW dichroic technology, i.e., can not be fixed for FM Filters

  11. OGSE Filters Filters

  12. OGSE Filter Status • Room temperature radiation from outside has to be attenuated to ~ telescope levels when using external sources. • Attenuation of a few 100 to be achieved by metal-on-mylar filters. • Needed attenuation values achieved on prototype filters But... Filters

  13. OGSE Filter Problems • Room temperature radiation from outside likely prevents proper cooldown of filters • Low thermal conduction (mylar, inconel stainless) • high absorptivity (10...50%) • Filter predicted temperatures above LN2 temperature, at emissivity ~ 30%==> remaining background levels factor ~10 too high Need additional cold 10um-absorbing or reflecting filter: -- cryst. Quartz (+) Availability (-) Redesign, ghost images, factor 3 -- QMC mesh filter (+)factor 1 (-) Schedule? Filters

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