Inkohärent

Inkohärent is a term used in optics and related fields to describe a wave field or signal whose phase relation is not fixed over time or space. In practice, an inkohärent source emits light or other waves whose phase varies randomly, so comparisons of phase over significant path differences do not produce stable, reproducible interference patterns.

Coherence is understood as having temporal and spatial components. Temporal coherence refers to the stability of the phase over time, closely related to the spectral bandwidth: broader bandwidth yields shorter coherence time. Spatial coherence concerns uniform phase across the wavefront; diffuse or extended sources have low spatial coherence. Inkohärente light thus typically has short temporal coherence and low spatial coherence.

Common inkohärent sources include the sun, incandescent lamps, and flames, which emit broad-spectrum, thermally excited radiation with uncorrelated phases. In contrast, lasers produce coherent light with high temporal and spatial coherence, exhibiting stable interference under suitable conditions.

The practical consequence of inkohärent light is that sustained interference fringes are difficult or impossible to observe over large path differences. Interferometric visibility degrades with increasing path difference beyond the coherence length. Imaging with incoherent light often results in speckle or just diffuse illumination, while coherent sources can produce sharp fringes and holographic features.

In summary, inkohärent describes signals lacking fixed phase relationships, characterized by broad spectra and limited coherence. This concept helps distinguish illumination and imaging scenarios that rely on incoherence from those that exploit coherence, such as interferometry, holography, and certain spectroscopy techniques.