Ph.D. Defense: Mala Mateen

    Tuesday, May 12, 2015 - 2:00pm
    Meinel 647

    “Development and Verification of the Non-Linear Curvature Wavefront Sensor”


    Adaptive optics systems have become an essential part of ground-based telescopes that enable diffraction-limited imaging at near-infrared and mid-infrared wavelengths. For several key science applications, the required wavefront quality is higher than what current systems can deliver. For instance, obtaining high-quality diffraction-limited images at visible wavelengths requires residual wavefront errors to be well below 100 nanometers root mean square. High-contrast imaging of exoplanets and disks around nearby stars requires high-accuracy control of low-order modes that dominate atmospheric turbulence and scatter light at small angles where exoplanets are likely to be found.

    Mateen's dissertation develops a highly sensitive nonlinear curvature wavefront sensor that can deliver diffraction-limited (λ/D) images, in the visible, by approaching the theoretical sensitivity limit imposed by fundamental physics. The nlCWFS is derived from the successful curvature wavefront sensing concept but uses a nonlinear reconstructor in order to maintain sensitivity to low spatial frequencies. The nlCWFS sensitivity makes it optimal for extreme AO and visible AO systems because it utilizes the full spatial coherence of the pupil plane as opposed to conventional sensors such as the Shack-Hartmann wavefront sensor, which operate at the atmospheric seeing limit (λ/r0). The difference is equivalent to a gain of (D/r0)2 in sensitivity, for the lowest order mode, which translates to the nlCWFS requiring that many fewer photons. When background-limited, the nlCWFS sensitivity scales as D4, a combination of D2 gain due to the diffraction limit and D2 gain due to telescope’s collecting power, whereas conventional wavefront sensors only benefit from the D2 gain due to the telescope’s collecting power. This is especially significant for upcoming extremely large telescopes such as the Giant Magellan Telescope, which has a 25.4-meter aperture, the Thirty Meter Telescope and the European Extremely Large Telescope, which has a 39-meter aperture.

    Speaker Bio(s): 

    Mala Mateen's committee is composed of Olivier Guyon, Michael Hart and José Sasián.