Vacuum ultraviolet spectropolarimeter design for precise polarization measurements

Area of Science:

• Astronomy and Astrophysics
• Solar and Stellar Physics
• Plasma Physics

Background:

• Weak magnetic fields in the Sun and stars' upper atmospheres are challenging to measure.
• Polarization measurements in the vacuum ultraviolet (VUV) region offer a novel approach.
• Previous methods lacked the precision required for detecting faint magnetic signals.

Purpose of the Study:

• To propose and detail a VUV spectropolarimeter design for precise magnetic field measurements.
• To adapt this design for the NASA-JAXA Chromospheric Lyman-alpha Spectropolarimeter (CLASP) mission.
• To measure the linear polarization (Stokes Q and U) of the hydrogen Lyman-α line.

Main Methods:

• A novel VUV spectropolarimeter design featuring two optically symmetric channels.
• A single concave diffraction grating acting as both a spectral disperser and beam splitter.
• Minimizing reflective components to achieve high VUV throughput and reduce polarization errors.

Main Results:

• The proposed design is adopted for the CLASP mission.
• The instrument will measure linear polarization of the hydrogen Lyman-α line profile.
• Expected polarization degree is approximately 0.1%, with minimized errors from flux variation and photon noise.

Conclusions:

• The developed VUV spectropolarimeter design is suitable for inferring weak magnetic fields.
• This instrument will enhance our understanding of solar and stellar atmospheric dynamics.
• The CLASP mission will provide unprecedented polarization data in the VUV.