What feature distinguishes coherent light sources from others?

Coherent light sources are characterized by emitting light waves that maintain a consistent frequency and phase relationship. This means that the light waves produced by these sources are in sync with each other, resulting in a stable interference pattern when the light interacts with itself or other surfaces. Coherence is crucial for numerous applications in optics, such as lasers and holography, where precise control over the light's properties is necessary for accurate imaging and measurements.

In contrast, sources that emit light with varying phases or in a random manner do not maintain this synchronization, leading to a scattered or jumbled interference pattern. Additionally, light that changes frequency while propagating lacks the stable phase relationship that defines coherence, affecting its utility in specific optical applications. This coherence effectively distinguishes light from sources like incandescent bulbs or sunlight from coherent sources like lasers.