Laser

About laser
LASER is an acronym and stands for Light Amplification by Stimulated Emission Radiation. It is a source of highly coherent electromagnetic radiation most commonly in the visible, ultraviolet or infrared part of a spectrum, which is generated by stimulated radiation emission of active particles (atoms, molecules, ions, electrons) excited by external energy source. This energy can be concentrated in a very short time. Emitted light is monochromatic.

Physical principle
See subpage: /Physical principle

The laser is based on the principle of stimulated (forced) radiation emission. Electrons in atoms of an active medium are first excited to the upper energy level, however they can not remain there therefore in a millionth of a second they jump to the working surface (metastable path). Due to the weak pulse in the form of a stimulating photon, deexcitation occurs associated with the emission of the same photon as the stimulating one. As a result, identical photons are produced, which are radiated in the same direction. The light has certain properties, including high coherence, high monochromaticity and low divergence.

Components
Pumping (emitting) radiation generates emission in the active substance which is bounded by paralel mirrors. After excitation of stimulated emission the light is reflected between the mirrors and it passes multiple through the active substance, which increases its intensity. After reaching sufficient intensity the parallel coherent beam leaks out through the semi-transparent mirror.

THE MAIN COMPONENTS OF LASER:
1. Active environment.

The active environment consists of a substance that contains separate quantum energy levels of electrons. It might be a solid substance with admixtures, a liquid or a mixture of gases.

2. Resonator.

The laser uses the resonator to amplify the light. The resonator in its simplest form is composed of two reciprocally paralel mirrors and at the same time perpendicular to the laser axis. One of them is nontransparent and the other one is semi-transparent. The mirrors are mostly planar but they could be also curved.

3.   Pump source.

The pump source is used to deliver energy to electrons in the active environment so they can move from a lower energy level to a higher energy level. Examples of a pump sources are an electric current, a discharge lamp, a chemical reaction or other lasers.

4.    Laser beam.

A laser beam comming out of an active environment through the semi-transparent mirror is coherent (non-diverging) and monochrome (unicoloured).

Types of lasers
According to the laser mode:
 * 1) Continuous lasers
 * 2) Pulse lasers
 * 3) Quasi-continuous lasers

According to the active environment:
 * 1) Ultrasonic lasers
 * 2) Semiconductors lasers
 * 3) Gas lasers
 * 4) Liquid lasers
 * 5) Plasma lasers
 * 6) Lasers with free electrons

Application
For applications in medicine, see subpage: /Application

Risks
The main risk of using laser is the possibility of eye damage. Some lasers work on frequencies that are captured and understood by the eye. Because laser is coherent and has low divergence, its beam is concetrated on a very small area of the retina, which overheats at certain point and can lead to permanent eye damage.

Related articles

 * Laser Issues