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] Lasers differ from other sources of light because they emit light coherently. Spatial coherence allows a laser to be focused to a tight spot, enabling applications like laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over long distances (collimation), enabling applications such as laser pointers. Lasers can also have high temporal coherence which allows them to have a very narrow spectrum, i.e., they only emit a single color of light. Temporal coherence can be used to produce pulses of light—as short as a femtosecond.
Lasers have many important applications. They are used in common consumer devices such as DVD players, laser printers, and barcode scanners. They are used in medicine for laser surgery and various skin treatments, and in industry for cutting and welding materials. They are used in military and law enforcement devices for marking targets and measuring range and speed. Laser lighting displays use laser light as an entertainment medium. Lasers also have many important applications in scientific research.
The domestic cat [1] [2] ( Felis catus [2] or Felis silvestris catus [4]) is a small, usually furry, domesticated, and carnivorous mammal. It is often called the housecat when kept as an indoor pet, [6] or simply the cat when there is no need to distinguish it from other felids and felines. Cats are often valued by humans for companionship and their ability to hunt vermin and household pests.
Cats are similar in anatomy to the other felids, with strong, flexible bodies, quick reflexes, sharp retractable claws, and teeth adapted to killing small prey. Cat senses fit a crepuscular and predatory ecological niche. Cats can hear sounds too faint or too high in frequency for human ears, such as those made by mice and other small animals. They can see in near darkness. Like most other mammals, cats have poorer color vision and a better sense of smell than humans.
Despite being solitary hunters, cats are a social species, and cat communication includes the use of a variety of vocalizations (mewing, purring, trilling, hissing, growling and grunting) as well as cat pheromones and types of cat-specific body language. [7]
Cats have a rapid breeding rate. Under controlled breeding, they can be bred and shown as registered pedigree pets, a hobby known as cat fancy. Failure to control the breeding of pet cats by neutering, and the abandonment of former household pets, has resulted in large numbers of feral cats worldwide, requiring population control. [8]
Since cats were cult animals in ancient Egypt, they were commonly believed to have been domesticated there, [9] but there may have been instances of domestication as early as the Neolithic from around 9500 years ago (7500 BC). [10]
A genetic study in 2007 concluded that domestic cats are descended from African wildcats (Felis silvestris lybica) c. 8000 BC, in the Near East. [9] [11] According to Scientific American, cats are the most popular pet in the world, and are now found in almost every place where humans live. [12]
