We are designing a telescope imaging system based on an apodized diffractive optical element called an apodized photon sieve (APS) in order to detect exoplanets. APSs are orders of magnitude less massive, lightweight and more compactable than mirrors. Proposed imaging system can be installed on any telescope as an "attachment" or used as a telescope itself as a part of a CubeSat payload. Methods were developed for designing the apodized sieves, measuring PSFs, and characterizing high-contrast performance of the imaging system. This new kind of APS has rotational symmetry and provides high-contrast (up to 10-10 levels) in all directions with just one image with the throughput of 40% or higher.
Quasi-static speckles are one of the main limitations in imaging exoplanets, since the image of a planet looks similar to a speckle. However, speckles are light from the same coherent source, the star, and incoherent with the planet. By moving the deformable mirror after each image, the speckle pattern as seen on the camera changes between images. The change is very small within the full width half max of the planet, so changes in the planet image are minimal. This fundamental coherence property of the speckles (and incoherence with the planet light) guides us to develop a planet detection method to distinguish a planet from a speckle by taking advantage of a changing speckle pattern. We present a planet detection algorithm using a Bayesian analysis. We seek to conduct a hypothesis test at each pixel in the image to detect the presence of a planet at that location. We formulate a test statistic and use a least-squares method to estimate the unknown parameters. These parameters are the intensities of a planet and a locally constant background. Our algorithm assumes the speckle pattern is independent from one image to another. This approach is used to formulate an integration time estimate for detection of a planet with specified probabilities of false alarms and missed detections. A comparison is made between a single stacked image and using multiple images.
The SCExAO instrument at the Subaru telescope, mainly based on a PIAA coronagraph can benefit from the addition of a robust and simple shaped pupil coronagraph. New shaped pupils, fully optimized in 2 dimensions, make it possible to design optimal apodizers for arbitrarily complex apertures, for instance on-axis telescopes such as the Subaru telescope. We have designed several masks with inner working angles as small as 2.5 λ / D, and for high-contrast regions with different shapes. Using Princeton University nanofabrication facilities, we have manufactured two masks by photolithography. These masks have been tested in the laboratory, both in Princeton and in the facilities of the National Astronomical Observatory of Japan (NAOJ) in Hilo. The goal of this work is to prepare tests on the sky of a shaped pupil coronagraph in 2012.
Current observations in the context of exoplanet searches with coronagraphic instruments have
shown that one of the main limitations to high-contrast imaging is due to residual quasi-static
speckles. Speckles look like the image of a planet, but they have a different spectral behavior
and are optically coherent with the star. We present two techniques to distinguish a planet from
speckles. We are assuming that the optical path can be changed enough so that the speckles
will change significantly between each image and therefore our model of each image having an
independent source of aberrations (creating a new speckle pattern) from the other images is a
good model. In the future, we would like to design and build a testbed suitable for coherent
speckle detection studies. There are two techniques we want to apply to create the necessary
multiple images with changing speckle patterns. The first is to use images generated using our
existing deformable mirror (DM) control algorithm and the second is to put deliberate shapes
on the DM to achieve the desired speckle pattern outcome.