Abstract Details
| Name: Ramya Anche Affiliation: IIA, Bengaluru Conference ID: ASI2019_473 Title : Polarization effects due to the segmented primary mirror of the Thirty Meter Telescope Authors and Co-Authors : Ramya Anche, G C Anupama, S Sriram and K Sankarasubramanian Abstract Type : Oral Abstract Category : Instrumentation and Techniques Abstract : The instrumental polarization (IP) and crosstalk (CT) due to the telescope optics affect the accurate polarimetric measurements. The next-generation telescopes such as Thirty Meter Telescope (TMT) consists of segmented primary mirror and inclined Nasmyth mirror. The effect of these two mirror configurations on the polarimetric measurements need to be estimated. Towards that, a polarization model for TMT has been already developed with primary mirror approximated as a monolith. Here, we present the results based on a more realistic approach considering the effect of individual segments. For the modelling, a total of 492 hexagonal segments are divided into six sectors with each sector having 82 unique segments. We have performed the polarization ray tracing in Zemax for this configuration. We have analysed the cases of missing segments and their effect on the Mueller matrices. We find that as the number of missing segments increases, though the I-> Q and U->V does not change considerably, the I->U, I->V and Q-> V components appear in the Mueller matrices. As a part of coating non-uniformity study, we generated six different coating recipes with 5-10% variation in the refractive index of silver. The Mueller matrices showed changes in the IP and CT elements. Along with these, the cases of random segment tilts and piston error on the Mueller matrices have been estimated. The variation in the piston of the segments is found to have no effect on the polarization measurements where as tilt in x and y directions causes changes in some of the Mueller matrix elements. As, none of the first-generation instruments for the telescope have a polarimetric capability, these estimations would help in the design aspects of a second-generation instrument with the polarimetric capability. |