rereflection

Rereflection, or re-reflection, is a term used in wave physics to describe a secondary reflection that occurs when a wave that has already been reflected encounters another reflective surface. The resulting backward-propagating component can interfere with the initial reflection, producing ghost images, additional echoes, or changes in intensity depending on geometry and material properties. Rereflection applies to light, sound, and other propagating waves and is relevant in the design and analysis of optical, acoustic, and electromagnetic systems.

In optics, rereflection contributes to ghosting and stray reflections in lenses, prisms, filters, and imaging sensors. It can create faint secondary images or interference fringes and may shift apparent focus. Designers mitigate rereflection with anti-reflective coatings, index-matching materials, careful surface geometry, and by angling interfaces to direct secondary reflections away from detectors.

In fiber optics and radar, rereflections appear as back-reflected signals that can destabilize light sources or clutter received data. In fiber networks they cause backscatter; in radar they appear as multipath or secondary echoes. Mitigation strategies include optical isolators, circulators, proper terminations, and impedance matching.

In architectural acoustics and non-destructive testing, rereflections contribute to late-arriving echoes and can complicate signal interpretation. Controlling them improves clarity in rooms and accuracy in diagnostics.

Terminology notes: rereflection is sometimes described as double reflection or secondary reflection, but it is generally used to denote a sequence of reflections beyond the initial event.