A Dual Fabry-Perot based imaging Spectrometer for the National Large Solar Telescope

Abstract

This report provides a detailed design of a dual Fabry-Perot based narrow band imaging system intended to make observations of solar atmosphere at visible and near infrared wavelengths. The narrow band imager will serve as one of the back end instrument planned for a proposed 2m class National Large Solar Telescope (NLST) by Indian Institute of Astrophysics. The narrow band imager comprises an air spaced, high reflectivity, large free spectral range Fabry-Perot interferometer. The instrument will have a spectral resolution of about 40 m°A to provide narrow band images of the solar atmosphere. The dopplergrams can also be made at a spatial resolution of 0.06 arcsec/ pixel. By combining it with the polarimeter, the narrow band imager can also provide magnetograms. Several simulations and numerical studies are carried out to arrive at the instrument design. The study of the important design parameters including optimum spacing ratio, field-of-view, optical layout, spectral and spatial resolution, signal-to-noise ratio etc is presented in detail. Finally, a comparison between the proposed instrument and similar instruments used in other solar observatories around the world is also made.