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Innovations in Variable-Delay Polarization Modulators (VPMs) for Precision Astronomy

This document discusses the advantages and applications of Variable-Delay Polarization Modulators (VPMs) in precision astronomy. VPMs provide intrinsic broadband performance and the capability to measure circular polarization, crucial for systematic instrument checks. Their design minimizes differential loss by using reflection methods rather than dielectrics and favors small linear motions for enhanced reliability. The integration of VPMs into the 350-micron, 32-pixel polarimeter Hertz at SMTO, Arizona, exemplifies their capability in advanced polarimetric measurements.

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Innovations in Variable-Delay Polarization Modulators (VPMs) for Precision Astronomy

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  1. Variable-delay Polarization Modulators (VPMs) D. Chuss, G. Novak 7/27/07

  2. Variable-delay Polarization Modulator(VPM)

  3. Advantages of VPMs • Can be made intrinsically broadband • Can measure circular polarization- a potentially useful systematic check of instrument • Used in reflection- no dielectrics to introduce differential loss. • Employs small, linear motions rather than large circular ones- A reliability issue.

  4. Hertz/SMTO NASA/GSFC: D. Benford, D. Chuss, M. Jackson, H. Moseley, J. Staguhn, G. Voellmer, E. Wollack Northwestern University: G. Novak, M. Krejny (GSRP) University of Arizona: C. Walker, C. D. d’Aubigny, C. Kulesa, D. Golish University of Chicago- R.F. Loewenstein Using a pair of VPMs, we have integrated the 350 micron, 32 pixel polarimeter Hertz onto the SMTO in Arizona.

  5. QVI 1: Selects Between Q & U (Grid wires at 22.5 degrees) QVI 2: Toggles Roles of detectors (Q->-Q) (Grid wires at 45 degrees)

  6. Dual Modulators

  7. Hertz/VPM

  8. Instrumental polarization- preliminary result Q=0.8 +/- 0.3% U=0.01 +/- 0.02% Data taken 4/24/07 Jupiter 29 observations tau~0.07, el=33 deg.

  9. NU Lab Tests- July 2007

  10. HAWC/VPM Integration

  11. VPM “Walkoff” Systematic • When placed at or near an image plane, the image formed by each polarization will be shifted relative to one another.

  12. Geometry

  13. Density Matrices Unpolarized Radiation Field Walkoff Polarization Modulation

  14. Unpolarized Airy Disk, 53 microns

  15. Analyzer misalignment: 1 degrees

  16. Image Translation (53 microns)

  17. Kilo-pixel Backshort-Under-Grid TES Arrays D. Chuss 7/27/07

  18. Basic TES Circuit Allen et al. (2006) Benford et al. IJIRMMW

  19. Time-Domain Multiplexing Irwin et al. (2004)

  20. GSFC BUG Architecture Allen et al. (2006) Staguhn et al. (2006)

  21. Pixel Frames Allen et al. (2006)

  22. Indium Bump-Bonding

  23. Large Format Arrays • 32 x 40 pixel arrays proposed as a continuation (ROSES) • These will be mated to the SCUBA MUXes • Pending funding, expected readiness date: late 2009 • Warm Electronics- suggest UBC source

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