Design requirements of a spectropolarimeter for solar extreme-ultraviolet observations and characterization of a K-mirror based on Brewster's angle
Measuring the linear polarization signal in extreme-ultraviolet (EUV) spectral lines, produced by the Hanle effect, offers a promising technique for studying magnetic fields in the solar corona. The required signal-to-noise ratio for detecting the Hanle polarization signals is on the order of 101 (off-limb) to 106 (disk center). Measuring such low signals in the photon starved observations demands highly efficient instruments. In this paper, we present the design of an instrument, SpectroPOLarimeter for Extreme-ultraviolet Observations (SPOLEO), which utilizes reflective components with suitable mirror coatings and thicknesses to minimize the throughput losses. We analyze the system performance within the spectral range from 740 to 800 The K-mirror-based polarimeter model provides a polarizing power of 20%40% in this wavelength range. Based on the system throughput and polarizing power, we discuss various possibilities for achieving the required signal-to-noise ratio, along with their limitations. Due to lack of facilities for fabrication and testing in the EUV, we have calibrated a prototype of the reflection-based polarimeter setup in the laboratory at the visible wavelength of 700 nm. 2024 Optica Publishing Group.
Khan R.; Dharmadhikari R.; Mathur H.; Nagaraju K.; Jain S.R.; Phanindra D.V.S.; Sagayanathan K.
Applied Optics, Vol-63, No. 34, pp. 8738-8747.
ISSN: 1559128X; PubMed ID: 39602680; CODEN: APOPA
https://doi.org/10.1364/AO.537460 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85210967116&doi=10.1364%2fAO.537460&partnerID=40&md5=e213331f98ec813db6d0f3769091f169
Khan R., Indian Institute of Astrophysics, Bengaluru, 560034, India, University of Calcutta, College Street, Kolkata, 700073, India, High Altitude Observatory, National Center for Atmospheric Research, Boulder, 80307, CO, United States; Dharmadhikari R., Indian Institute of Astrophysics, Bengaluru, 560034, India, University of Calcutta, College Street, Kolkata, 700073, India; Mathur H., Indian Institute of Astrophysics, Bengaluru, 560034, India, University of Calcutta, College Street, Kolkata, 700073, India; Nagaraju K., Indian Institute of Astrophysics, Bengaluru, 560034, India; Jain S.R., Christ University, Bengaluru, 560034, India; Phanindra D.V.S., Indian Institute of Astrophysics, Bengaluru, 560034, India; Sagayanathan K., Indian Institute of Astrophysics, Bengaluru, 560034, India