Aperture masking interferometry

The method was developed by John E. Baldwin and collaborators in the Cavendish Astrophysics Group at the University of Cambridge in the late 1980s.

Each pair of holes provides a set of fringes at a unique spatial frequency in the image plane.

Partially redundant masks are usually designed to provide a compromise between minimizing the redundancy of spacings and maximizing both the throughput and the range of spatial frequencies investigated (Haniff & Buscher 1992; Haniff et al. 1989).

Although the signal-to-noise of speckle masking observations at high light level can be improved with aperture masks, the faintest limiting magnitude cannot be significantly improved for photon-noise limited detectors (see Buscher & Haniff 1993).

This is enabled by a non-redundant mask with seven holes (sub-apertures), which is embedded as a mode of the NIRISS instrument.

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.