Lasers

The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation. The light we usually see is a mixture of wavelengths that are out of step with each other whereas light produced by a laser contains only one wavelength and the waves are coherent i.e. in step with each other. Laser light is made by feeding energy into a solid, liquid or gas. As the substance absorbs energy, the atoms become excited and release light of one particular wavelength. When light from one atom strikes its neighbours, more light is released. The light produced is reflected by mirror at either end of the laser so that it surges back and forth inside with the intensity rising each time the light travels form one end to the other. Eventually the light becomes so intense it passes through one of the mirrors forming a laser beam.
The first laser was built in 1960 by Theodore Maiman. It consisted of a cylinder of synthetic ruby a few centimeters long surrounded by a spiral lamp with a built in cooling system.
Laser beams are used by surgeons to weld or cut the human body with great accuracy. For example, if the retina comes loose from the eye, a helium-neon laser can be shone through the pupil to weld the retina back in position. Lasers are also used in engineering and manufacturing. They can be used to measure distance by using the interference that is produced when a laser beam is split and reflected back by different surfaces. By analysing interference fringes the distance between two objects can be worked out accurately. Lasers are also used to cut through or join together many different materials from cloth to metal as when directed onto a surface they can produce an intense heat.