SUNRISE III is an international balloon-borne solar observatory with a 1m diameter telescope and is scheduled to fly in 2022. The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is being developed as a focal plane instrument for SUNRISE III, which will perform multi-wavelength spectropolarimetric observations with high spatial and spectral resolution (0.21 arcsec and 2 × 105 ). The SCIP is a quasi-Littrow-type spectropolarimeter mainly composed of an echelle grating and two aspheric mirrors. A polarizing beam splitter is used for simultaneous measurement of p- and s-polarization. To ensure the imaging performance, correct the image rotation and shift, and avoid vignetting, we performed the optical alignment. The optical elements were firstly aligned by shimming with mechanical precision of 1-20 arcmin for tilt and 0.1-0.3 mm for shift using a coordinate measuring machine. After the mechanical alignment, we constructed the telecentric feed optical system to mimic the light distribution instrument of SUNRISE III telescope, which is called Image Stabilization and Light Distribution (ISLiD). To reduce the astigmatism, we measured the contrast of the spot in the spatial direction and the width of the spot in the wavelength direction and adjusted the two aspheric mirrors. For the correction of the image rotation, the Z-tilt of grating was adjusted with a wavelength tunable laser by evaluating the tilt of the slit image in the wavelength direction. The wavelength position in cameras was adjusted with tunable lasers and sunlight. We evaluated the modulation transfer function of SCIP using a Ronchi ruling target with a white light source.
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