Design and Basic Calibration of a Scanning Fabry Perot Cavity Towards Atomic Spectroscopy in the Solar Oscillation and Magnetic Imager (SOMI) Instrument

Ashar, Unnati (2019) Design and Basic Calibration of a Scanning Fabry Perot Cavity Towards Atomic Spectroscopy in the Solar Oscillation and Magnetic Imager (SOMI) Instrument. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The study of the Sun to enhance our space weather forecasting capabilities is an accepted necessity. An instrument called the SOMI- Solar Oscillation and Magnetic Imager has been proposed by CESSI for the Aditya L5 space mission concept of ISRO to study the solar photospheric Fe-I line centred at 6173 Å. The SOMI instrument will consist of a Fabry-Perot (FP) based spectrum analyser and a Polarization State Analyser (PSA) unit. Both of these will work in tandem to generate intensity, Doppler velocity and magnetic field data of the solar surface. This thesis deals with the FP based spectrum analyser part of the SOMI instrument. The FP is tasked with scanning the 6173 Å solar absorption line at five points, the data obtained from which will be analysed along with the data from the PSA unit to generate filtergrams, dopplergrams and magnetograms. As the 6173 Å line itself is just 0.1 Å wide, the FP needs to be extremely narrow-band to extract faithful information. This thesis attempts to provide proof of concept for various targets vis-à-vis the FP. It was demonstrated successfully that an in-house FP can be built which can act as a narrow-band filter extracting the exact required wavelength even with a broadband white light source. Further, a proposed technique for extracting the source spectrum from the FP fringes also produced results as expected. This thesis thus sets the base for further improvements of the FP proposed by the SOMI team.

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