coherent light is a light in which the electromagnetic waves maintain a fixed and predictable phase relationship with each other over a period of time.
Additional Information (S)
Incoherent light contains may different wavelengths and amplitudes of light, such as light from a light bulb. Coherent light is a beam of light where all of the photons are the same frequency and interval. If you think of photons like people, a laser is a coherent group of photons like a column of soldiers marching in a long parade, whereas incoherent light is more like everyone exiting from the movie theater.
Incoherent light is light that has varying phases and wavelengths. It is not focused or organized like coherent light. Incoherent light is commonly used in everyday lighting, photography, and displays. It is also used in medical treatments, such as photodynamic therapy.
The photons (units of light) in incoherent light fly around like, say pepper and water in a blender. The photon in LASER light all move in the same direction like soldiers marching together down a street. LASER light is 'Coherent' light. This means that a beam of coherent light can travel great distances without spreading out.
Coherent sources are required to produce interference of light because they have a constant phase difference between them. This phase relationship allows the light waves to either reinforce or cancel each other out, creating distinct interference patterns. Incoherent sources have random phase relationships, leading to a lack of interference effects.
First let us remove the word visible from this question and replace it with incoherent, as visible light can be either coherent or incoherent and coherent light can be either inside the visible spectrum or outside it.Incoherent light is random/unordered, e.g. wave phases different, shines in all directions, polychromatic.Coherent light is ordered in one or more ways, e.g. wave phases all synchronized, shines in one unidirectional collimated beam, monochromatic.The difference between light in the visible spectrum or outside it is only whether humans can see it or not, there is no difference in the light itself other than wavelength.
Laser light is said to be coherent; regular light such as the type produced by an incandescent bulb is incoherent. In coherent light, all the wavelengths are the same, and all the directions are the same, everything lines up and is perfectly uniform. With incoherent light, you get a messy mixture of wavelengths and directions. Light from a laser is collimated - i.e. aligned such that all the light rays are oriented parallel to each other. For this reason, you do not see laser light unless some of it is deflected by striking a something in its path or you are looking directly at it. In a filament lamp, the light rays are oriented in nearly all directions.
A laser light is coherent, meaning its waves are all in phase and directional, giving a narrow beam. In contrast, light from a white flashlight is incoherent and spreads out in various directions. Laser light also has a single color (wavelength), while white light contains a mix of colors.
COHERENT WAVESWhen the light waves are emitted from a single source and they have the zero phase difference between them then the waves are said to be coherent. The coherent waves are shown below:
A laser beam is a coherent light source that emits a narrow beam of light due to the alignment of its waves. In contrast, light from a tube light is incoherent and emits light in all directions, resulting in a blurry appearance. The difference in coherence and directionality between laser light and tube light accounts for their distinct characteristics.
LEDs, known as light emitting diodes, are comprised of two lead semiconductor light sources. Laser transmitters, also known as laser diodes are comprised of an electrically charged semiconductor laser.
Coherent sources are sources of waves that have a constant phase difference between them. An example of coherent sources is two identical lasers emitting light waves with the same frequency and wavelength.
Identical light waves in phase are called coherent light waves. Coherent waves have a constant phase difference between them, which allows for constructive interference and the formation of interference patterns.
The main difference is that laser light is coherent, meaning the light waves are aligned and moving in a single direction, while ordinary white light is non-coherent, with light waves traveling in random directions. Laser light is also monochromatic, meaning it consists of a single color, while white light contains a mixture of different colors.