Aperture masking interferometry

a) shows a simple experiment using an aperture mask in a re-imaged aperture plane. b) and c) show diagrams of aperture masks which were placed in front of the secondary mirror of the Keck telescope by Peter Tuthill and collaborators. The solid black shapes represent the subapertures (holes in the mask). A projection of the layout of the Keck primary mirror segments is overlaid.

Aperture masking interferometry (or Sparse aperture masking) is a form of speckle interferometry, that allows diffraction limited imaging from ground-based telescopes (like the Keck Telescope and the Very Large Telescope), and is a high contrast imaging mode on the James Webb Space Telescope. This technique allows ground-based telescopes to reach the maximum possible resolution, allowing ground-based telescopes with large diameters to produce far greater resolution than the Hubble Space Telescope. A mask is placed over the telescope which only allows light through a small number of holes. This array of holes acts as a miniature astronomical interferometer. The principal limitation of the technique is that it is applicable only to relatively bright astronomical objects, since the mask discards most of the light received from the astronomical source. The method was developed by John E. Baldwin and collaborators in the Cavendish Astrophysics Group at the University of Cambridge in the late 1980s.