Laser

The Laser

Definition :

A Laser is device that creates and amplifies electromagnetic radiation of a specific frequency through the process of stimulated emission. The radiation emitted by a laser consists of a coherent beam of photons, all in phase and having the same polarization.
A laser emits a thin, intense beam of nearly monochromatic visible or infrared light that can travel long distances without diffusing. Most light beams consist of many waves traveling in roughly the same direction, but the phases and polarizations of each individual wave (or photon) are randomly distributed. In laser light, the waves are all precisely in step, or in phase, with each other, and have the same polarization. Such light is called coherent. All of the photons that make up a laser beam are in the same quantum state. Lasers produce coherent light through a process called stimulated emission. The laser contains a chamber in which atoms of a medium such as a synthetic ruby rod or a gas are excited, bringing their electrons into higher orbits with higher energy states.

When one of these electrons jumps down to a lower energy state (which can happen spontaneously), it gives off its extra energy as a photon with a specific frequency. But this photon, upon encountering another atom with an excited electron, will stimulate that electron to jump down as well, emitting another photon with the same frequency as the first and in phase with it.
This effect cascades through the chamber, constantly stimulating other atoms to emit yet more coherent photons. Mirrors at both ends of the chamber cause the light to bounce back and forth in the chamber, sweeping across the entire medium. If a sufficient number of atoms in the medium are maintained by some external energy source in the higher energy statea condition called population inversionthen emission is continuously stimulated, and a stream of coherent photons develops. One of the mirrors is partially transparent, allowing the laser beam to exit from that end of the chamber. Lasers have many industrial, military, and scientific uses, including welding, target detection, microscopic photography, fiber optics, surgery, and optical instrumentation for surveying.

Schematic:

How it work ?

A laser is an optical oscillator, which is can be made out of a solid, liquid or gas. It contains two with mirrors at both ends: one is totally reflecting and the other only partially. To make it work, the material is excited or "pumped," with an energy source such as light or electricity.

When this energy source gives energy the electrons in the atoms, they become excited. But the interesting part is when a few of the electrons drop back to lower energy levels spontaneously, and then release a photon (or a quantum of light). The photons created stimulate other excited electrons and emit more and more photons. Then the light waves (photons), which passes through the laser medium, is reflected by the mirrors at both ends. It keeps the light back and forth creating a chain reaction. After that, the light beam goes out through the output.

Uses of Laser:

Gas Lasers

A specific type of laser is the gas laser. There are many types of gas lasers, as each one uses a specific type of gas to create the laser emission. For example, a helium-neon laser uses HeNe to produce varied wavelengths. Because of the flexibility of this laser light, it can be created through a low budget, making it especially useful in education institutions and other organizations with limited funding.

Chemical Lasers

Another type of laser is a chemical laser, which is created through artificially induced chemical reactions. These chemical lasers are capable of high energy outputs and deliver consistent emissions, making them very useful for machines and equipment that require continuous operation.

Excimer Lasers

Excimer lasers also call on the power of chemical reactions. Although not in every single case, they usually tend to create ultraviolet light and are used in semiconductor photolithography and in LASIK eye surgery. LASIK eye surgery has become a commonplace procedure, allowing patients to receive treatment and return home the same day.

Solid State Lasers

Solid-state lasers are among the most useful lasers that exist today, finding applications in a number of different arenas. This laser technology is used on a daily basis, including materials processing, such as welding and cutting. Solid-state lasers are also used in semiconductor fabrication, graphic arts and medical and surgical operations and procedures.

Pointers

Laser lights are also used as simple, harmless laser pointers for school and office presentations. These handy devices help people point to exact locations on slides, helping them deliver smooth-flowing, precise presentations. Some are even used in cat toys as the animals enjoy chasing the beam up the wall.

Entertainment

Another popular use of laser lights is for entertainment purposes, such as light shows at theme parks, special effects in movies and stage effects for concerts.

Applications of Laser :

The laser is part of our daily life. Many examples…

The laser pointer used in classrooms	The CD in a computer or in a hi-fi that are used to read the data stored in a CD.
In industry, laser is often used for cutting and microscopic processing.	For military purposes, laser is used to intercept guided missiles.
Lasers are used to measure distance.