Abstract
The next generation of ground-based optical telescopes, such as the European Southern Observatory’s Extremely Large Telescope (the ELT), will have large support structures (spiders) for the secondary mirror. These spiders have the effect of segmenting the pupil. Without careful control of the wavefront, segment piston (petal modes) errors can develop. We present a flip-flop modulated/unmodulated method for the pyramid wavefront sensor (PWFS) enabling the PWFS to sense petal piston modes. This flip-flop modulation method uses a single PWFS operating in two states: a modulated state and an unmodulated state. An independent controller is used in each state; the modulated state controls the atmospheric turbulence and the unmodulated state only controls petal piston modes. In simulation, we show the flip-flop method working with the wavefront sensor in both K- and R-bands, providing an improvement of 9.9% and 13%, respectively, over a standard modulated PWFS.
Highlights
The generation of ground-based astronomical telescopes and associated instrumentation are currently under development
Adaptive optics (AO) systems are used to measure and correct the blurring effects of the turbulence in real time using a wavefront sensor (WFS) to measure wavefront errors caused by the atmosphere and a deformable mirror (DM) to correct for them.[4,5]
A nominal wavelength of 650 or 2200 nm is used for both the point spread function (PSF) and the WFS, in R- and K-bands, respectively
Summary
The generation of ground-based astronomical telescopes and associated instrumentation are currently under development. These so-called extremely large telescopes (ELTs) comprise the European Southern Observatory’s (ESO) Extremely Large Telescope (the ELT),[1] the Giant Magellan Telescope,[2] and the Thirty Meter Telescope.[3]. Earth’s time-varying turbulent atmosphere limits the achievable resolution of ground-based telescopes. The resulting detector plane consists of four pupil images, which are used to estimate the wavefront. The PWFS has a small dynamic range, when compared with an SHWFS, because the sensor is only in the linear region when the focal spot is on the apex of the pyramid. A method to overcome the limited dynamic range is to modulate the
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