Coherent Light

Have you ever wondered why a laser beam is different from other light sources? Well, in schools, you would have rattled off coherent light definition several times, but did you ever think why lasers produce a straight, narrow beam of light? The reason is that the laser light is monochromatic in nature. A light source is said to be monochromatic if it consists of a single wavelength of light or other radiation. The ordinary light that we see everyday like sunlight or electricity is not coherent, each source of light comes from different atoms, whereas on the other hand coherent light is created by stimulated emissions. The research on coherent light is still going on, but many of the theories of coherent light are still unclear.

How is a Coherent Beam Produced?
To understand how coherent beams are produced, let us take the example of how a coherent light 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.

Significance of Coherent Light
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. Coherent light 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 light. Some of the uses of Xenon light are

• It is used in photographic flashes, stroboscopic lamps and solar simulators.
• Xenon light is also used as 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.
• Xenon light also finds its use in plasma display 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. Although it is a vast topic, I hope this information would be useful for you to understand what is coherent light and some of the other basic things about coherent light.