Polarization Properties of a Birefringent Fiber Optic Image Slicer for Diffraction-Limited Dual-Beam Spectropolarimetry

摘要

The birefringent fiber optic image slicer design, or BiFOIS, adapts integral field spectroscopy methods to the special needs of high-sensitivity, spatially-resolved spectropolarimetry. In solar astronomy these methods are of particular importance, as dynamic magnetism lies at the heart of various multi-scaled phenomena in the solar atmosphere. While integral field units (IFU) based on fiber optics have been in continual development for some time, standard stock multimode fibers do not typically preserve polarization. The importance of a birefringent fiber optic IFU design stems from the need for dual-beam spatio-temporal polarimetric modulation to correct for spurious polarization signals induced either by platform jitter or atmospheric seeing. Here we characterize the polarization response of a second generation BiFOIS IFU designed for solar spectropolarimetry. The unit provides 60 × 64 spatial imaging pixels in a densely-packed, high filling factor configuration. Particular attention is placed on the spatial uniformity of the IFU polarization response. Calibrated first-light solar observations are also presented to demonstrate the performance of the device in a real application.