Abstract Details

Name: Radhika Dharmadhikari
Affiliation: Indian Institute of Astrophysics
Conference ID: ASI2021_250
Title : Phasing Segmented Primary Mirror using the Dispersed Fringe Technique
Authors and Co-Authors : Radhika Dharmadhikari (IIA, Bangalore), Padmakar Parihar (IIA, Bangalore)
Abstract Type : Oral
Abstract Category : Instrumentation and Techniques
Abstract : The segmented mirror technology is being extensively used these days to build large astronomical telescopes, so that higher resolution and sensitivity can be achieved with the lower manufacturing costs. In order to achieve diffraction limited image quality, the alignment and phasing errors of segments, should be minimized. We have extensively explored the Dispersed Fringe Sensor (DFS) with an aim to use it for phasing the primary mirror made of small segments. In the presence of the phase error, the DFS phasing technique, which uses a broadband light source and dispersive element, forms fringes in the continuum spectra. These fringes are manifestations of coherent summing of the reflected light from two segments, subjected to the piston error. The number of the fringes (frequency) and their visibility is a measure of the piston error. A python code has been developed to simulate the fringe spectra based on the basic principle of DFS. Then after the simulation tool has been used to study the effects of various parameters on the fringe spectra. Also the effect of various noises, including the photon noise and the CCD introduced noises were studied. The curve fitting tool in python was used to extract the piston value from the simulated fringe images. We have also attempted to design the optics of the DFS instrument, planned to be used in Prototype Segmented Mirror Telescope for the purpose of phasing as well as coarse alignment. In my presentation, I will briefly describe the DFS technique, the algorithm used in the simulation as well as some results obtained. Efforts made towards designing the optics of the DFS instrument is also briefly covered in my presentation.