Aperture Masking Interferometry

Technique

Aperture Masking Interferometry is alternative to direct imaging that offers increased resolution and increased contrast range on ground and space telescopes.

By introducing a small mask with several holes in the telescope pupil plane, the full aperture is converted into an ad-hoc interferometric array.  The point spread function is converted from an Airy function to a set of over-lapping fringes.  The longest baseline of the array is the diameter of the telescope, nominally increasing the resolution of the telescope to 0.5 lambda/D, less than half the diffraction limit of the full aperture (i.e., super-resolution).

Furthermore, using a data analysis technique borrowed from radio interferometry called closure phases, aperture masking measurements are less corrupted by large scale atmospheric noise (speckle noise).  This reduction in noise allows for higher contrast images than those obtained with adaptive optics alone.  Especially within a few lambda/D, aperture masking allows the detection of companions one to several magnitudes fainter.

Aperture masks are currently installed in the PHARO Infrared detector on the Palomar Hale 200" Telescope and at Keck.  Our group has detected several brown dwarf companions at high contrast and at separations well within the formal diffraction limit.  The precision of our measurements is, generally, a factor of a few better than those obtained with direct imaging alone.

The combination of aperture mask techniques and Integral Field Spectrographs, such as Project 1640 and the Gemini Planet Imager, will provide unsurpassed contrast and the diffraction limit.  Already, preliminary results with Project 1640 and an aperture mask show that an increase in contrast of a factor of 10x over conventional aperture masking may be routinely obtained.

Additionally, an aperture mask will be installed in the TFI on JWST.  This configuration is expected to provide contrasts of 1,000,000:1 at the diffraction limit in one hour of observation, enough to image Jupiter-analogs forming around young solar-type stars.

Research Statement: High-Angular Imaging & Aperture Masking

Selected Presentations and Posters:

    Smaller, Fainter, Closer: Finding Stellar Companions using Aperture Masking Interferometry
       Invited Talk for American Museum of Natural History, NYC, April 2010

    Brown Dwarf Masses with Aperture Masking Interferometry and Radial Velocity
       Poster for Precision Radial Velocity Workshop at Penn State University, August 2010

    Brown Dwarf Masses with Aperture Masking Interferometry and Laser Guide Star Adaptive Optics
       Poster for Palomar Science Meeting at Caltech, May 2009