Integration and calibration of a multi slit spectropolarimeter

Abstract

Multi-slit spectropolarimeter is a next-generation spectropolarimeter to obtain vector magnetic field information at high spatial, spectral, and temporal resolution for studying the magnetic structures on the Sun. Once developed, it can be used as ground based instrument at solar observatories, also as a space payload for various solar missions. A high spectral resolution is invariably an important parameter for accurate vector magnetic field measurements and faster cadence is required for the study of dynamical evolution of structures (e.g., solar flares, sunspots etc.) on the Sun and hence better understanding on the physics behind their evolution.The multi-slit spectropolarimeter mainly consists of a spectrograph, polarimeter package and an area-array detector (CCD camera). The spectrograph consists of multi-slit (5-slits), diffraction grating, collimator and camera lens system. Integration of the polarimeter and detector is achieved by using a LabVIEW GUI platform. User controllable options for camera and LCVR settings were developed in LabVIEW. The CCD camera operation for capturing images is synchronized with the clock used to switch the voltage supplied to the LCVR. This is achieved by providing an external trigger signal from LCVR to camera. Acquisition of data is carried out through CCD into a widely used FITS format along with the experimental settings and other required information. This is achieved using the LabVIEW GUI developed. A calibration curve for voltage versus retardance for LCVR was obtained using an experimental setup. Multi-slit spectrograph was calibrated by filling all the slits using a laser source. Preliminary study of the instrument’s polarization response was carried for linearly polarized input.