Abstract

We present the first measurements and scientific observations of the solar photosphere obtained with a new two-dimensional polarimeter based on piezoelastic modulators and synchronous demodulation in a CCD imager. This instrument, which is developed for precision solar-vector polarimetry, contains a specially masked CCD that has every second row covered with an opaque mask. During exposure the charges are shifted back and forth between covered and light-sensitive rows synchronized with the modulation. In this way Stokes I and one of the other Stokes parameters can be recorded. Since the charge shifting is performed at frequencies well above the seeing frequencies and both polarization states are measured with the same pixel, highly sensitive and accurate polarimetry is achieved. We have tested the instrument in laboratory conditions as well as at three solar telescopes.

© 1994 Optical Society of America

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References

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  1. H. P. Povel, H. Aebersold, J. O. Stenflo, “Charge-coupled device image sensor as a demodulator in a 2-D polarimeter with a piezoelastic modulator,” Appl. Opt. 29, 1186–1190 (1990).
    [CrossRef] [PubMed]
  2. H. S. Stockman, “Differential imaging using charge-coupled image device (CCD) imagers with on-chip charge storage,” in Instrument in Astronomy IV, D. L. Crawford, ed., Proc. Soc. Photo-Opt. Instrum. Eng. 331, 76–80 (1982).
  3. C. U. Keller, F. Aebersold, U. Egger, H. P. Povel, P. Steiner, J. O. Stenflo, “Züich imaging Stokes polarimeter ZIMPOL I—design review,” LEST Tech. Rep. 53 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).
  4. J. C. Kemp, “Piezo-optical birefringence modulators,” J. Opt. Soc. Am. 59, 950–954 (1969).
  5. I. Yadigaroglu, “Prototype CCD solar polarimeter: evaluation experiments and calibration,” term thesis (Eidgenössische Technische Hochschule, 1991).
  6. D. J. Thorne, N. R. Waltham, G. M. Newton, I. G. van Breda, M. Fisher, P. J. Rudd, “CCD guidance system for the William Herschel telescope,” in Instrumentation in Astronomy VII, D. L. Crawford, ed., Proc. Soc. Photo-opt. Instrum. Eng. 1235, 400–412 (1990).
  7. J. O. Stenflo, C. U. Keller, H. P. Povel, “Demodulation of all four Stokes parameters with a single CCD ZIMPOL II—conceptual design,” LEST Tech. Rep. 54 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

1990 (1)

1969 (1)

Aebersold, F.

C. U. Keller, F. Aebersold, U. Egger, H. P. Povel, P. Steiner, J. O. Stenflo, “Züich imaging Stokes polarimeter ZIMPOL I—design review,” LEST Tech. Rep. 53 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

Aebersold, H.

Egger, U.

C. U. Keller, F. Aebersold, U. Egger, H. P. Povel, P. Steiner, J. O. Stenflo, “Züich imaging Stokes polarimeter ZIMPOL I—design review,” LEST Tech. Rep. 53 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

Fisher, M.

D. J. Thorne, N. R. Waltham, G. M. Newton, I. G. van Breda, M. Fisher, P. J. Rudd, “CCD guidance system for the William Herschel telescope,” in Instrumentation in Astronomy VII, D. L. Crawford, ed., Proc. Soc. Photo-opt. Instrum. Eng. 1235, 400–412 (1990).

Keller, C. U.

C. U. Keller, F. Aebersold, U. Egger, H. P. Povel, P. Steiner, J. O. Stenflo, “Züich imaging Stokes polarimeter ZIMPOL I—design review,” LEST Tech. Rep. 53 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

J. O. Stenflo, C. U. Keller, H. P. Povel, “Demodulation of all four Stokes parameters with a single CCD ZIMPOL II—conceptual design,” LEST Tech. Rep. 54 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

Kemp, J. C.

Newton, G. M.

D. J. Thorne, N. R. Waltham, G. M. Newton, I. G. van Breda, M. Fisher, P. J. Rudd, “CCD guidance system for the William Herschel telescope,” in Instrumentation in Astronomy VII, D. L. Crawford, ed., Proc. Soc. Photo-opt. Instrum. Eng. 1235, 400–412 (1990).

Povel, H. P.

H. P. Povel, H. Aebersold, J. O. Stenflo, “Charge-coupled device image sensor as a demodulator in a 2-D polarimeter with a piezoelastic modulator,” Appl. Opt. 29, 1186–1190 (1990).
[CrossRef] [PubMed]

C. U. Keller, F. Aebersold, U. Egger, H. P. Povel, P. Steiner, J. O. Stenflo, “Züich imaging Stokes polarimeter ZIMPOL I—design review,” LEST Tech. Rep. 53 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

J. O. Stenflo, C. U. Keller, H. P. Povel, “Demodulation of all four Stokes parameters with a single CCD ZIMPOL II—conceptual design,” LEST Tech. Rep. 54 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

Rudd, P. J.

D. J. Thorne, N. R. Waltham, G. M. Newton, I. G. van Breda, M. Fisher, P. J. Rudd, “CCD guidance system for the William Herschel telescope,” in Instrumentation in Astronomy VII, D. L. Crawford, ed., Proc. Soc. Photo-opt. Instrum. Eng. 1235, 400–412 (1990).

Steiner, P.

C. U. Keller, F. Aebersold, U. Egger, H. P. Povel, P. Steiner, J. O. Stenflo, “Züich imaging Stokes polarimeter ZIMPOL I—design review,” LEST Tech. Rep. 53 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

Stenflo, J. O.

H. P. Povel, H. Aebersold, J. O. Stenflo, “Charge-coupled device image sensor as a demodulator in a 2-D polarimeter with a piezoelastic modulator,” Appl. Opt. 29, 1186–1190 (1990).
[CrossRef] [PubMed]

C. U. Keller, F. Aebersold, U. Egger, H. P. Povel, P. Steiner, J. O. Stenflo, “Züich imaging Stokes polarimeter ZIMPOL I—design review,” LEST Tech. Rep. 53 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

J. O. Stenflo, C. U. Keller, H. P. Povel, “Demodulation of all four Stokes parameters with a single CCD ZIMPOL II—conceptual design,” LEST Tech. Rep. 54 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

Stockman, H. S.

H. S. Stockman, “Differential imaging using charge-coupled image device (CCD) imagers with on-chip charge storage,” in Instrument in Astronomy IV, D. L. Crawford, ed., Proc. Soc. Photo-Opt. Instrum. Eng. 331, 76–80 (1982).

Thorne, D. J.

D. J. Thorne, N. R. Waltham, G. M. Newton, I. G. van Breda, M. Fisher, P. J. Rudd, “CCD guidance system for the William Herschel telescope,” in Instrumentation in Astronomy VII, D. L. Crawford, ed., Proc. Soc. Photo-opt. Instrum. Eng. 1235, 400–412 (1990).

van Breda, I. G.

D. J. Thorne, N. R. Waltham, G. M. Newton, I. G. van Breda, M. Fisher, P. J. Rudd, “CCD guidance system for the William Herschel telescope,” in Instrumentation in Astronomy VII, D. L. Crawford, ed., Proc. Soc. Photo-opt. Instrum. Eng. 1235, 400–412 (1990).

Waltham, N. R.

D. J. Thorne, N. R. Waltham, G. M. Newton, I. G. van Breda, M. Fisher, P. J. Rudd, “CCD guidance system for the William Herschel telescope,” in Instrumentation in Astronomy VII, D. L. Crawford, ed., Proc. Soc. Photo-opt. Instrum. Eng. 1235, 400–412 (1990).

Yadigaroglu, I.

I. Yadigaroglu, “Prototype CCD solar polarimeter: evaluation experiments and calibration,” term thesis (Eidgenössische Technische Hochschule, 1991).

Appl. Opt. (1)

J. Opt. Soc. Am. (1)

Other (5)

I. Yadigaroglu, “Prototype CCD solar polarimeter: evaluation experiments and calibration,” term thesis (Eidgenössische Technische Hochschule, 1991).

D. J. Thorne, N. R. Waltham, G. M. Newton, I. G. van Breda, M. Fisher, P. J. Rudd, “CCD guidance system for the William Herschel telescope,” in Instrumentation in Astronomy VII, D. L. Crawford, ed., Proc. Soc. Photo-opt. Instrum. Eng. 1235, 400–412 (1990).

J. O. Stenflo, C. U. Keller, H. P. Povel, “Demodulation of all four Stokes parameters with a single CCD ZIMPOL II—conceptual design,” LEST Tech. Rep. 54 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

H. S. Stockman, “Differential imaging using charge-coupled image device (CCD) imagers with on-chip charge storage,” in Instrument in Astronomy IV, D. L. Crawford, ed., Proc. Soc. Photo-Opt. Instrum. Eng. 331, 76–80 (1982).

C. U. Keller, F. Aebersold, U. Egger, H. P. Povel, P. Steiner, J. O. Stenflo, “Züich imaging Stokes polarimeter ZIMPOL I—design review,” LEST Tech. Rep. 53 (Institute of Theoretical Astrophysics, University of Oslo, Oslo, 1992).

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Figures (8)

Fig. 1
Fig. 1

Cross section through the modified EEV P86223/M1 CCD imager.

Fig. 2
Fig. 2

Dark-current signal as a function of temperature from −5 to +20 °C. Top curve, without demodulation; bottom curve, with 50-kHz demodulation. The curves are the same at 100 kHz. The demodulation reduces the dark current significantly.

Fig. 3
Fig. 3

Gain table for a 30 × 30 region of the image with flat illumination and 50-kHz demodulation. The masked and exposed rows are visible because of the demodulation asymmetry (see text).

Fig. 4
Fig. 4

Stokes I of a sunspot near the disk center without correction for the gain table. Note the contamination by the fringes. The two strong lines near the center are the two Fe i lines near 6302 Å.

Fig. 5
Fig. 5

Simultaneous Stokes V/I of the sunspot shown in Fig. 4. Solid black and white corresponds to ±10% circular polarization. Note the absence of any gain table or charge-transfer efficiency defects.

Fig. 6
Fig. 6

Stokes Q/I of a sunspot near the solar limb. The spectral region is the same as in Figs. 4 and 5. Solid black and white corresponds to ±5% linear polarization. Note again the absence of any gain table or charge-transfer efficiency defects.

Fig. 7
Fig. 7

Stokes profiles of a single spatial point in a sunspot with 2-s exposure time observed in poor seeing conditions at the German Vacuum Tower Telescope. The left line is Fe i 5250.2 Å, and the right one is Fe i 5247.1 Å. The absorption feature between the two lines is due to the prism system used to combine the two lines on a single CCD chip.

Fig. 8
Fig. 8

Broadband circular polarization near the solar limb near 4500 Å. The upper panel shows the white-light image where the dark patch is a sunspot and the brighter areas are faculas. Both are magnetic structures. The lower panel shows the circular polarization signal resulting from the net asymmetry of the Stokes V signals in magnetic areas. Solid black and white corresponds to ±0.15% circular polarization.

Equations (5)

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S + = I + ( 1 + ζ ) c 1 + I - ( 1 - ζ ) c 2 + d + ,
S - = I - ( 1 - ζ ) c 1 + I + ( 1 + ζ ) c 3 + d - .
P obs = S + - S - S + + S - = P 2 c 1 - c 2 - c 3 2 c 1 + c 2 + c 3 + c 2 - c 3 2 c 1 + c 2 + c 3 1 - P c 2 - c 3 2 c 1 + c 2 + c 3 .
P obs 0 = c 2 - c 3 2 c 1 + c 2 + c 3 ,             P obs + = c 1 - c 3 c 1 + c 3 ,             P obs - = c 1 - c 2 c 1 + c 2 .
P = P obs - P obs 0 ½ ( P obs + - P obs - ) + P obs 0 P obs .

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