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.
