1. Calibration of the Polarization Property of SOT K.Ichimoto, Y.Suematsu, T.Shimizu, Y.Katsukawa, M.Noguchi, M.Nakagiri, M.Miyashita, S.Tsuneta (National Astronomical Observatory of Japan, Mitaka, Tokyo, JAPAN) T. D. Tarbell, R. A. Shine, C. M. Hoffmann, T.Cruz (Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA USA) B. W. Lites, D. F. Elmore (High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO USA) and SOT Team Solar-B Science Meeting #6, 2005.11.8-11 in Kyoto Abstract Calibration of SOT polarization property was performed during the natural sunlight test of SOT in June 2005 using a heliostat at Mitaka. Well calibrated sheet polarizers (linear and circular) was placed on the OTA to control the incident Stokes vector, and the polarimeter response matrix, X, was determined for the spectropolarimeter (SP) and the narrowband filter instrument (NFI), where X is defined by S out = X S in (S in : incidence Stokes vector, S out : product of SOT by the onboard demodulation). The crosstalk between I,Q,U,V will be negligible after the calibration with the obtained X matrix at photometric accuracy of 10 -3. The sensitivity of SOT on polarization (and also on magnetic fields) at all wavelengths observed by Narrowband Filter Instrument (NFI) are also discussed. 1. The polarization measurement error and SOT requirement assumed matrix real matrix The polarization measurement error can be given by :  S = S ” -S = { (XT) r -1 XT- E } S ≡ D   (XT) S  0.3333 0.3333 0.2500 0.0010 0.0500 0.0067 0.0050 0.0010 0.0067 0.0500 0.0050 0.0010 0.0067 0.0067 0.0500 SOT requirement on accuracy of XT is,, Crosstalks among I,Q,U,V should be negligible at  = 0.1% S ’ = XT S = SOT product after onboard demodulation S “ = (XT) r -1 S ’ = reduced Stokes vector after calibration  (XT) < Flow to get the Stokes vector from a polarimeter if (XT) r = XT +  (XT)  E +  (XT) Scale error  = 0.001 (photom.accuracy) a = 0.05 (scale tolerance) P l = 0.15 (max. linear pol.) P v = 0.2 (max. circular pol.) 3. Test configuration Sheet polarizer window (I,Q,U,V) mask FPP Heliostat Polarization calibration of entire SOT was performed during natural sunlight using a heliostat at Mitaka. June 2005 @NAOJ cleanroom Well calibrated three sheet polarizers are put on the telescope entrance at every 45 deg.. SOT coordinate HNCP37R 1.0000 0.9866 0.0000 0.0428 0.1052 0.1047 0.0000 0.0043 -0.1064 -0.1057 0.0000 -0.0044 0.9811 0.9763 0.0001 0.0425 transmission= 0.346 HNCP37L 1.0000 0.9868 0.0000 -0.0432 0.0032 0.0034 0.0002 -0.0001 -0.0636 -0.0633 0.0001 0.0027 -0.9905 -0.9853 -0.0002 0.0430 transmission= 0.354 HN38 1.0000 0.9916 0.0000 0.0025 0.9989 0.9969 0.0000 0.0022 0.0145 0.0145 0.0000 - 0.0003 0.0000 0.0008 0.0003 - 0.0006 transmission= 0.358 Mueller matrix of sheet polarizers Q U V 4. Data reduction SOT products x ij are determined by least square fitting, together with some unknowns of polarizers. Example of least square fitting Polarizer /angle k = 1 ~ 12 angle 0 45 90 135 0 45 90 135 0 45 90 135deg. Incident Stokes vectors determined by polarizers c R = P lR cos2  R, V R = 0.9811 s R = P lR sin2  R, P lR = 0.1496 c L = P lL cos2  L, V L = 0.9905 s L = P lL sin2  L, P lL = 0.0637 P l = 0.9990 RCP LP LCP Symbols: observed Lines: fitting results 2. Strategy of SOT polarization control The SOT polarization has been controlled in various steps, 1 ) Optical elements (glass, coating, etc.) 2) Optical assemblies (CLU, CTM-TM, etc) 3) Polarimeter (FPP + CTM-TM + PMU) 4) Entire SOT  sun test 5) In orbit Element and component level testings help a lot to select the best optical elements and to make entire SOT a reliable polarization instrument. OTA:  50cm Gregorian Telescope FPP: HDM (Heat Dump Mirror) M2 M1 2ndary field stop CLU (collimator Lens Unit) PMU (Polarizaiton Modulator Unit) Tip-tilt mirror In this poster presentation, polarization calib. for entire SOT using sunlight is focused. 5. Spectro-Polarimeter Left 1.0000 0.2205 0.0187 -0.0047 0.0012 0.4813 0.0652 -0.0014 0.0001 0.0513 -0.4803 -0.0057 -0.0025 0.0032 -0.0046 0.5256 Right 1.0000 -0.2112 -0.0170 -0.0051 -0.0025 -0.4875 -0.0560 0.0022 -0.0001 -0.0426 0.4907 0.0060 0.0027 -0.0008 0.0042 -0.5301 Median Mueller matrix x matrices at scan center; CCD image The x matrix can be regarded as uniform in the CCD. Each point is the median in the CCD, scale = average + 0.01, dotted horizontal lines show tolerances for each element x-matrix elements vs. the scan position Asterisk: Left CCD Diamond: right CCD The x matrix can be regarded as constant over the scan position each element is scaled to median + tolerance, x 00 (=1) is replaced by I-image Left 0.0000 0.0157 -0.0046 0.0064 0.0016 0.0105 -0.0041 0.0031 0.0012 -0.0047 0.0088 0.0012 -0.0024 0.0038 -0.0005 0.0073 Right 0.0000 -0.0332 -0.0027 -0.0155 0.0086 -0.0065 -0.0019 -0.0098 -0.0016 0.0049 -0.0087 -0.0019 0.0015 -0.0063 0.0016 -0.0037 repeatability Measurements of two successive days are compared. dx = x(on 6/14) - x(on 6/13), scan center, median value Repeatability of measurement except the first column are within the SOT tolerance. (See also Lites etal. ) 6. Narrowband Filter Instrument (NFI) Example of X matrix over the CCD, 5172, shutterless, 80x1024 left: theta= -1.571deg. 1.0000 -0.2994 -0.0336 -0.0435 0.0009 -0.4544 0.0208 0.0045 -0.0009 0.0287 0.4478 0.0068 -0.0085 0.0318 -0.0134 0.5774 right: theta= -4.441deg. 1.0000 -0.2871 -0.0305 -0.0434 -0.0003 -0.4473 0.0653 0.0038 -0.0007 0.0738 0.4435 0.0061 -0.0077 0.0310 -0.0150 0.5718 Sensitivity of NFI to linear and circular polarization are determined for each wavelengths of NFI X matrix for NFI shutterless mode can be regarded as uniform in each left and right half of the CCD, but they have a mutual rotation of about 2.8deg. Retardation of the waveplate 7. Detection limit of NFI for weak magnetic fields The MgI517.2 line provides opportunities for diagnosing the vector magnetic fields in lower chromosphere, NaI 589.6nm is suitable for measuring the line of sight component of B in lower chromosphere. H  has no sensitivity on the transversal field. Results: Detection limit of NFI for weak magnetic fields,  = 0.001 1) Diagonal elements of x-matrix give the polarization sensitivity of SOT Q z, V z are Zeeman signal in spectral line Q p, V p are SOT response 2) Detection limit of Q p, V p are given by the photometric accuracy in spectral line  is photometric accuracy in continuum ~ 0.001 3) Zeeman singnal (Q z, V z ) in weak magnetic field can be given by the assumption that the Zeeman effect is a simple separation of I-profile 4) Thus detection limit for the magnetic fields are given Line profile convoluted with the tunable filter profile Steps of evaluation Summary -‘SOT polarization response matrix’ (X) for use in flight operation are determined with the required accuracy. -X matrix of SP can be regarded as uniform over each left and right CCD and for the scan positions. -X matrix for NFI shutterless mode can be regarded as uniform in each left and right half of the CCD, but they have a mutual rotation of about 2.8deg. which should be corrected in the data reduction. -We suggest to determine the first columns of the X matrix more accurately after launch using the continuum in data obtained in orbit. -The sensitivity of SOT on polarization at each wavelength observed by NFI was evaluated, together with its capability for detecting the weak magnetic fields. -The MgI517.2 line provides opportunities for diagnosing vector magnetic fields in lower chromosphere, NaI 589.6nm is suitable for measuring the line of sight component of B in lower chromosphere, while H  has no sensitivity on the linear polarization.