The Calibration of the Advanced Stokes Polarimeter
The Calibration of the Advanced Stokes Polarimeter
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DOI：
10.1086/313004
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发表时间：
1997-06
期刊：
影响因子：
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通讯作者：
A. Skumanich;B. Lites;V. Pillet;P. Seagraves
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文献类型：
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作者：
A. Skumanich;B. Lites;V. Pillet;P. Seagraves
我们描述和应用了已经发展起来的校准高级斯托克斯偏振仪和补偿国家太阳天文台/太阳黑子真空塔望远镜引入的偏振效应的方法。利用对太阳盘中心和太阳黑子本影中磁场定向尽可能接近视线的点的观测，将望远镜的七参数模型与在各种镜角下获得的数据进行了拟合。偏振器本身的响应矩阵是通过使用偏振校准光学装置来确定的，该偏振校准光学装置修改了离开望远镜但在进入偏振器之前的光束的偏振状态。同时得到了响应矩阵和望远镜参数的全局最小二乘解。描述了一种详细的增益校正过程，该过程将光谱图像中的倍增增益误差降低到通常小于1%。在仪器产生的≃1-5×10-2Ic背景极化下，我们成功地恢复了峰值为1×10-3Ic的净线偏振分布。在背景中，即使有足够的平均，小于≃3×10-4Ic的净偏振信号也会由于光度和其他校准误差而丢失。
We describe and apply the methods that have been developed to calibrate the Advanced Stokes Polarimeter and to compensate for the polarization effects introduced by the Vacuum Tower Telescope at the National Solar Observatory/Sunspot. A seven-parameter model of the telescope is fitted to data obtained at a variety of mirror angles using observations of both the center of the solar disk and that point within a sunspot umbra at which the magnetic field is oriented as close to the line of sight as possible. The response matrix of the polarimeter itself is determined by the use of polarizing calibration optics that modify the polarization state of the beam exiting the telescope but before entering the polarimeter. A global least-squares solution is obtained simultaneously for the response matrix and the telescope parameters. A detailed gain-correction procedure is described that reduces the multiplicative gain errors in the spectral images to typically less than 1%. We have successfully recovered net-linear polarization profiles with peak amplitudes of 1 × 10-3Ic against an instrumentally produced background polarization of ≃1-5 × 10-2Ic. Net-polarization signals smaller than ≃3 × 10-4Ic are lost, even with sufficient averaging, in a background due to photometric and other calibration errors.