The In 1916 Albert Einstein proposed stimulated emission,

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The LaserBefore we can learn about the laser we need to know a little bit aboutlight (since that is what a laser is made of). Light from our sun, or from anelectric bulb, is called white light. It is really a mixture of all thedifferent colours of light. The colours range from violet, indigo, and blue, togreen, yellow, orange, and red.

These make up the visible part of theelectromagnetic spectrum. Light is made up of particles, called PHOTONS, whichtravel in waves. The difference in the colour depends on the wavelength of thelight. Violet light has the shortest wavelength while red has the longest. Thereare other parts of the electromagnetic spectrum which includes infra-red, radar,television radio and micro- waves (past red on the spectrum), and on the otherend of the spectrum are the other invisible radiations, ultra- violet, X rays,micro waves and gamma rays. The wavelength of the light is important to thesubject of the laser.

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A laser is made up of COHERENT light, a special kind oflight in which the wavelengths of the light are all the same length, and thecrests of these waves are all lined up, or in PHASE. The word Laser is anacronym for Light Amplification by Stimulated Emission of Radiation. What doesthat mean? Basically a laser is a device which produces and then amplifies lightwaves and concentrates them into an intense penetrating beam.The principles of the laser (and it’s cousin the maser) were establishedlong before these devices were successfully developed. In 1916 Albert Einsteinproposed stimulated emission, and other fundamental ideas were discussed by V.A.Fabrikant in 1940. These ideas, followed by decades of intensive development ofmicrowave technology set the stage for the first maser (a laser made up ofmicro-waves), and this in turn helped to produce more advances in this area ofscience.

These efforts cumulated in July 1960 when Theodore H. Maiman announcedthe generation of a pulse of coherent red light by means of a ruby crystal– thefirst laser.Laser light is produced by pumping some form of energy, such as light, froma flash tube (see below) into a LASING material, also known as a medium. Mediacan be liquids, solids, gases, or a mixture of gases, such as the common helium-neon laser (see chart). Each medium produces a laser with a different wavelengthand therefore each medium produces different coloured light.

When the energy, inthis case photons (light particles) enter the medium they smash into the atomsof the medium. The atom then releases another photon of a specific wavelength.When a loose photon hits an atom that hasn’t emitted it’s extra photon, bothphotons are released. That is called stimulated emission of radiation. A singleflash from a flash lamp emits billions of pairs of photons into the medium. Thephotons are then released as coherent light.The first laser, a ruby laser, was made up of several main components.

Ithad a flash tube coiled around a central rod of synthetic pink ruby. In thiscase the ruby is the medium. A quartz tube was located just underneath the rubyrod. A trigger electrode was connected to the quartz tube. All of this wasenclosed in a polished aluminum casing.

This was cooled by a forced air supply.This design was thought to be good enough but later an optical resonatorwas added to redirect light in the right direction which increased laserperformance. The optical resonator was a mirror at one end of the laser toredirect light back into the laser and a partially reflective laser which letssome coherent light through.Today there are many types of lasers which include solid state lasers,which have a solid media. The most common of this is a rod of ruby crystals andneodymium-doped glasses and crystals. These offer the highest energy output ofall lasers. Another laser type is the gas laser, which can be made of a pure gasor a mixture of gases or even a vaporized metal in a quartz tube. The helium-neon laser has hight frequency stability and Carbon Dioxide lasers are the mostefficient and powerful continuous wave lasers.

The most compact type of laser isthe Semiconductor laser, made from layers of sem i-conducting materials. Sincethese can run by direct application of electrical current these have many uses,such as CD players and laser printers. Liquid lasers


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