Single shot solar spectroscopic design aspects

Abstract

High time-cadence Spectro-Polarimetry allows the feasibility of studying magnetic field evolution coupled with the plasma flows. Such a high cadence solar spectro-polarimetry if developed will allow one to study magnetic field evolution in eruptive processes like solar flares, prominence eruptions, etc. A single shot solar spectroscopy was recently demonstrated at Multi-application Solar Telescope (MAST) at Udaipur Solar Observatory. The snapshot spectroscopy is performed by sampling the pupil plane using the lenslet array to get multiple images of the field of view (FOV), which are then collimated and the collimated beam is made to pass through an FP Etalon in collimated mode. As the distance from the FP axis increases, the peak transmitted wavelength shift towards the bluer side. Using a pre-filter with a full width half maximum (FWHM) less than the free spectral range (FSR) of FP, combined with an imaging lens, we can get multiple images of FOV on image plane with a blue shift in spectra as we move radially outwards from the optical axis.

We have made an optimized Zeemax design utilizing the above concept for Multi-application Solar Telescope (MAST) at Udaipur Solar Observatory and also demonstrated the concept using available components and collected sample data.

We have made a Zeemax design of the Snapshot Spectrograph for the Daniel K. Inouye Solar Telescope (DKIST), carried out tolerance analysis through Monte-Carlo simulations and presented the Spot diagrams and PSF for the worst and best case scenarios.

We have also attempted to demonstrate snapshot spectro-polarimetric concepts in IIA Optics Lab. We have used Stokes definition polarimeter i.e. a linear analyzer and a quarter wave plate combination as a polarimeter. We have used He-Ne laser followed by a linear polarizer as a light source and collimated it from a 50-micron pinhole, the collimated beam is incident upon the lenslet array making multiple images of the pinhole, images are further collimated and made to pass through the FP and imaged at the detector. We have presented the results of this experiment i.e. Stokes parameters.