Why is laser light described as being coherent?

Laser light is described as being coherent because it is made up of waves that have a constant phase relationship. This means that the waves of laser light are not only of the same wavelength, but they also oscillate in unison. Coherence is a critical characteristic of lasers, as the photons emitted are in phase with one another, leading to a highly organized and uniform light beam. This property allows laser light to maintain its intensity over long distances and to be focused into very tight beams, which is fundamentally different from other light sources that emit waves with various wavelengths and phases.

Understanding coherence is essential in numerous applications, such as interferometry, holography, and telecommunications, where the properties of laser light can be utilized effectively. Other light sources, like incandescent bulbs or LEDs, emit light that is more chaotic in terms of wavelength and phase, leading to less control over the light's behavior.