UNIQUE PROPERTIES OF LASER l LECTURE 4

This channel is free for all worldwide students: SCIENCE STUDY BY KHAN A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term " laser " originated as an acronym for " light amplification by stimulated emission of radiation " .[1][2] The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories , based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow.A laser differs from other sources of light in that it emits light coherently , spatially and temporally. Spatial coherence allows a laser to be focused to a tight spot , enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances (collimation) , enabling applications such as laser pointers. Lasers can also have high temporal coherence , which allows them to emit light with a very narrow spectrum , i.e. , they can emit a single color of light. Temporal coherence can be used to produce pulses of light as short as a femtosecond.Among their many applications , lasers are used in optical disk drives , laser printers , and barcode scanners; DNA sequencing instruments , fiber-optic and free-space optical communication; laser surgery and skin treatments; cutting and welding materials; military and law enforcement devices for marking targets and measuring range and speed; and laser lighting displays in entertainment.