Study on the effects of mount induced errors, temperature induced errors and basic alignment errors of TMT primary mirror segments on the image quality using PSSN metric

Abstract

Thirty meter telescope is one of the new class of extremely large telescopes which have a segmented primary mirror of thirty meter of total aperture that consists of 492 hexagonal segments. Several error sources like passive alignment parameters (piston, tilt etc.), gravity induced effects, temperature induced effect contributes to the total science loss in the instrument. To optimize the optical performance of the telescope all possible error sources should be studied and characterized using some optical performance metric. During this project I have studied some passive alignment parameters like piston and tilt, mount induced effect due to gravity and the effects of temperature change. I have got the optical performance in some traditional metric like RMS WFE or 80 percent encircled energy diameter separately for different error sources. But as the error sources provide a wide spatial frequency bandwidth, none of them is reliable to give us a complete picture. So, a non-traditional optical performance metric, normalized point source sensitivity metric (PSSN), is used to characterize the optical performance of the telescope. The advantages of this metric are - it is reliable for errors having a wide frequency bandwidth and it is multiplicative in nature. So, we can get the complete picture by multiplying the PSSN values achieved by analysing each error sources separately. In this thesis the detailed study of the effects of the abovementioned errors is presented. The PSSN values for these errors were calculated separately and by multiplying them the total science loss due to those three error sources was calculated.