# Developments of Multi-wavelength Spectro-Polarimeter on the Domeless Solar Telescope at Hida Observatory

## TL;DR

This paper presents a newly developed multi-wavelength spectro-polarimeter for the Domeless Solar Telescope, enabling simultaneous full Stokes spectra acquisition across multiple wavelengths to improve solar magnetic field diagnostics.

## Contribution

The paper introduces a novel multi-wavelength spectro-polarimeter with advanced calibration and high sensitivity, capable of simultaneous observations in multiple spectral windows.

## Key findings

- Instrumental polarization characterized and calibration established.
- Cross-talk among Stokes parameters minimized to 0.06%-1.2%.
- Achieved sensitivity of 0.03% in 20-60 seconds across 500-1100 nm.

## Abstract

To obtain full Stokes spectra in multi-wavelength windows simultaneously, we developed a new spectro-polarimeter on the Domeless Solar Telescope at Hida Observatory. The new polarimeter consists of a 60 cm aperture vacuum telescope on an altazimuth mount, an image rotator, a high dispersion spectrograph, polarization modulator and analyzer composed of a continuously rotating waveplate with a retardation nearly constant around 127$^{circ}$ in 500 - 1100 nm and a polarizing beam splitter located closely behind the focus of the telescope, fast and large format CMOS cameras and an infrared camera. The slit spectrograph allows us to obtain spectra in as many wavelength windows as the number of cameras. We characterized the instrumental polarization of the entire system and established the polarization calibration procedure. The cross-talks among the Stokes Q,U and V are evaluated to be about 0.06% $sim$ 1.2% depending on the degree of the intrinsic polarizations. In a typical observing setup, a sensitivity of 0.03% can be achieved in 20 - 60 second for 500 nm - 1100 nm. The new polarimeter is expected to provide a powerful tool to diagnose the 3D magnetic field and other vector physical quantities in the solar atmosphere.