Which description best defines coherent light?

The description that best defines coherent light is the one stating that it is light with an electric vector related by a continuous function. Coherent light refers to light waves that are in phase with each other, which means their peaks and troughs align consistently over time and space. This property allows coherent light sources, like lasers, to produce highly focused and monochromatic beams.

Coherent light exhibits a stable phase relationship, which is crucial for applications such as interferometry and holography, where the interference patterns of light waves are utilized. The continuous function aspect indicates that the light maintains a consistent relationship in terms of frequency and phase, enhancing its ability to maintain directionality and coherence over long distances.

The other descriptions are not accurate representations of coherent light. Dispersed light describes a phenomenon where light spreads out, which contradicts the focused nature of coherent light. Random emissions relate more closely to incoherent light, where the phase and frequency of light waves vary unpredictably. Lastly, variation in wavelength indicates a lack of coherence, as coherent light ideally has a single wavelength rather than a range. Thus, the properties of coherent light discussed emphasize its unique characteristics that distinguish it from other forms of light.