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Things Physics Enthusiasts Would Want to Know About Coherent Light

Rahul Pandita Jun 3, 2019
Coherent light is a form of light in which the electromagnetic waves maintain a set and predictable phase relationship with each other, over a period of time.
A light source is said to be monochromatic if it consists of a single wavelength of radiation. In the ordinary light that we see everyday, like sunlight, each source comes from different atoms, whereas coherent light is created by stimulated emissions. The research on this topic is still going on, but many of the theories are still unclear.

How is it Produced?

To understand how coherent beams are produced, let us take the example of how a laser was invented. In the spring of 1960, Theodore Maiman constructed the first laser at the Hughes Research laboratories. Maiman used a small synthetic rod with silvered ends and exposed the rod to light.
On exposure to light, the chromium atoms in the rod became excited producing enough energy for photons to break through one of the silver ends of the ruby rod, to emit coherent light. The result was a beam of monochromatic light, the wavelength of which was 694 nanometers.

Coherence Time

Coherence time is defined as the time over which a propagating electromagnetic wave may be considered coherent (τ). It is calculated as τ = λ2 / cΔλ
where λ is the wavelength of the source, Δ is the spectral width, and c is the velocity of light in vacuum.


One of the most important significance of coherent light is its use in eye treatment. Because of laser eye surgery, many blind people have been able to see again. It is also used for construction purposes in the form of lasers.

Linac Coherent Light Source

The linac coherent light source (LCLS) produces pulses of X-rays more than a billion times brighter than the most powerful existing sources, the so-called synchrotron sources, which are also based on large electron accelerators.
The ultrafast X-ray pulses are used much like flashes from a high-speed strobe light, enabling scientists to take stop-motion pictures of atoms and molecules in motion, shedding light on the fundamental processes of physics, technology, and life itself.

(Source: Stanford University)

Xenon Light

Xenon is a colorless, heavy element with atomic number 54. Xenon gas is used for light emitting devices, known as Xenon lights.
  • It is used in photographic flashes, stroboscopic lamps, and solar simulators.
  • It is also used in arc lamps and high intensity discharge headlights.( Remember the advert of the car mentioning its xenon headlights)
  • It has been used for anesthetic purposes, although it is expensive.
  • It also finds use in plasma displays for televisions.
Coherent light is useful in so many ways that scientists all over the world are keenly researching its other uses, like treatment in cancer, etc.