What type of laser produces a coherent beam of light?

A coherent beam of light refers to light waves that are in phase in space and time, exhibiting a uniform frequency and a consistent direction. Continuous wave (CW) lasers are designed to emit a steady and uninterrupted beam of light, which ensures that the emitted photons maintain the same phase relationship over time. This consistent emission characteristic is what defines the coherence of the light produced by CW lasers.

While other types of lasers, such as pulsed, diode, and fiber lasers, can also produce coherent light under certain conditions, CW lasers are specifically recognized for their continuous output, making them a primary example of coherent light sources. Pulsed lasers, though they can produce a coherent output during the pulse duration, do not maintain coherence continuously as they emit light in short bursts. Diode lasers and fiber lasers may also produce coherent beams, but they are often classified based on their operation principles rather than their coherence characteristics. Thus, continuous wave lasers stand out as a clear representation of a laser that consistently delivers a coherent beam of light throughout its operation.