coherence of light

COHERENCE OF LIGHT

Coherence refers to the ability of light rays to travel, closely packed in straight lines and parallel in a beam. The light rays hold together and seem to “cohere,” making what we usually call a sunbeam. This property of light is not common, but it occurs occasionally in our everyday lives.

The clear examples are

•the laser, an instrument that emits visible light with great coherence i.e. minimum divergence from the constant diameter of the beam over a long distance.

• automobile headlights seen through fog or theatrical spotlights, in which the reflector portions of the lamp (light bulb) direct light rays so that they concentrate in a narrow beam and strike a well defined spot on a surface.

• intense, direct sunlight, is occluded by a defined opening—an opening in a wall, for example—defining a beam of light that streams into a space.

Coherent Light

Coherent light are light waves that are "in phase" with one another.

For example, two waves are coherent if the crests of one wave are aligned with the crests of the other and the troughs of one wave are aligned with the troughs of the other.

Otherwise, these light waves are considered incoherent.

Assignment:

HOW LASERS WORK

Short Bond Paper1 cm margin aroundOne Page, including a colored diagram and explanationHand-drawn, Hand-writtenDue: Nov 28/29,2011, whichever is later.