codedmask

A coded mask is a type of aperture mask used in high-energy astrophysics and imaging systems to enable the indirect imaging and localization of celestial sources, particularly in X-ray and gamma-ray wavelengths. Unlike traditional optical lenses or mirrors, coded masks consist of a pattern of opaque and transparent elements arranged in a specific design, typically a grid or a pseudo-random array. This pattern casts a shadow or a "coding" onto a detector placed behind the mask, which records the combined shadow patterns of multiple sources within the field of view.

The primary advantage of coded mask techniques lies in their ability to image in energy ranges where traditional focusing optics are not feasible or are limited by high photon energies. By mathematically decoding the recorded shadow patterns, scientists can reconstruct the position and intensity of sources within the observed region. Coded masks are particularly useful for detecting transient events, such as gamma-ray bursts, and for surveys of large sky regions.

Different coded mask patterns, such as uniformly redundant arrays (URAs) or modified grids, are optimized to maximize image quality, sensitivity, and resolution. The technique requires complex algorithms for image deconvolution and source localization, but it provides a wide field of view and high angular resolution compared to some other indirect imaging methods.

Coded mask systems are employed in several space-based observatories, including instruments like the Burst Alert Telescope (BAT) on the Swift satellite. Their design facilitates high-energy observations that are crucial for understanding phenomena such as black holes, neutron stars, and cosmic explosions.