Within the next decade, the world will see a new generation of telescopes with diameters up to 40m, called the Extremely Large Telescopes [ELTs]. One of the most exciting promises of ELTs is the detection and characterization of exoplanets. Astronomers have developed adaptive optics (AO) systems to compensate in real time the effects of atmospheric turbulence on image quality. Extreme adaptive optics (exAO) systems in combination with state-of-the-art coronagraphs take these corrections to a new level to provide the contrast and resolution needed to see these faint, small objects. All of the ELTs implement pyramid wavefront sensors (PWFS) in the design of their adaptive optics systems to provide high precision wavefront sensing and control. The Pyramid Wave Front Sensor (PWFS) is based on optical Fourier filtering: light at the focal plane is split using a glass Pyramid, and then reimaged into pupil images which contain phase information encoded as intensity variations. Although pyramid wavefront sensors are now common place in astronomy adaptive optics, much remains to be learned about their fundamental sensitivities to wavefront aberrations. In particular, low-order aberrations seriously affect the performance of coronagraphs used for high-contrast exoplanet imaging.
To optimize a high contrast pyramid wavefront sensor for a ELT exAO system, we are developing the theoretical framework of a three-sided pyramid wavefront sensor (3PWFS). The 3PWFS should have a higher photon efficiency and therefore be more sensitive to wavefront aberrations than the traditional four-sided pyramid wavefront sensor (4PWFS) in the presence of noise. I present preliminary results of an experiment comparing the performance of 3PWFS and 4PWFS in end-to-end simulations using the Object Oriented Matlab Adaptive Optics Toolbox (OOMAO). To demonstrate the validity of the simulation, I demonstrate the performance of a 3PWFS using the LOOPS testbench at the Laboratoire d'Astrophysique de Marseille. I present the design of the LOOPS testbench, including the Spatial Light Filter (SLM) that we place at the focal plane to generate the pyramidal optics. Current results from the LOOPS testbench will be shown.