Diffractionuseful

Diffractionuseful is a term used in wave optics to describe the portion of a diffracted wave field that can be effectively captured and used by a measurement system. It contrasts with the total diffracted energy, which includes portions that are lost to the detector geometry, obscured by noise, or fall outside the instrument’s bandwidth. The concept emphasizes practical information content rather than total radiometric energy.

Mathematically, diffractionuseful can be defined as the integral of the intensity over the region in the detector or analysis space that lies within the system's transfer function and contributes to the recovered signal. It depends on wavelength, aperture, numerical aperture, detector size, and geometry. In Fraunhofer diffraction, the useful portion is the part of the diffraction pattern that lies within the optical transfer function support; in imaging, it relates to encircled energy and the point spread function.

Applications of the concept appear in the design and analysis of telescopes, microscopes, cameras, and antennas, where diffraction spreads energy but may still preserve informative content. Designers may use the notion of diffractionuseful to compare how different apertures, detectors, or sampling schemes retain usable information despite diffraction effects.

Diffractionuseful is not an established standard metric; it overlaps with concepts such as encircled energy, Strehl ratio, and the modulation transfer function. It can help frame trade-offs between resolution, sensitivity, and practical information content, but its definition and scope can vary between contexts, affecting comparability.

See also: diffraction, diffraction-limited imaging, optical transfer function, point spread function, signal-to-noise ratio.