Sensing petal piston modes with a pyramid wavefront sensor
Department of Electrical and Computer Engineering
Time & Place
Fri, 23 Oct 2020 14:00:00 NZDT in Link 309 Lecture Theatre
The European extremely large telescope has a secondary mirror support structure (spider) which consists of six arms, with a width of 0.5m. This has the effect of subdividing the pupil into six segments or petals. The typical r0 at the observatory site is smaller than that of the spider arms, leading to a scenario where the turbulence is discontinuous from petal to petal. This introduces a problem where the average wavefront over each petal is different (petal piston modes), which can have a detrimental effect on the point spread function. I propose a new approach to solve the issue of differential petal piston, using a pyramid wavefront sensor with hybrid modulation (switching between modulated and unmodulated). The unmodulated pyramid wavefront sensor can be used to sense and correct petal piston modes in the presence of closed-loop adaptive optics residuals, even in R-band (650nm). This method is advantageous as it could correct petal piston that is present in the atmosphere and that which is introduced by the telescope structure (low wind effect).