Lasers 3 (Click to select text)

The idea for the laser started as long ago as 1905 when Albert Einstein suggested the simulated emission of light. Light sources ie. candles, florescent substances, torches, and light bulbs give of packets of energy, called photons, when their atoms are excited by energy. Einstein suggested that these atoms could be artificially stimulated to emit photons, where the light produced would be highly concentrated, bright and powerful and could be used for many tasks. Even though Einstein new the principals for building a laser, it was not attempted until later because it would be to expensive and difficult at that time since the advanced machinery that was needed did not exist yet. It was not until the 1950's where the stage was set to build a laser. Charles Townes, a scientist, wanted to see if microwaves, which are very similar to light, might be stimulated to produce an amplified beam by the process that Albert Einstein described. Townes was successful in 1954 when he constructed what he called the maser (microwave amplification by stimulated emission of radiation). The maser amplifies the number of photons that cause microwaves. After the invention of the maser many scientists became interested in the idea of building an optical maser, which soon received the name laser (light amplification by stimulated emission of radiation). Townes paired with Arthur Schawlow, two Soviets, Nikolai Basov and Aleksander Prokhorov, as well as Gordon Gould were all interested in developing a light-amplifying device. All of them knew that there were three essential ingredients in making a laser; a florescent material that would emit light when stimulated by radiation from an external energy source, two facing mirrors on the sides of the florescent material, and external energy source. Theodore Maiman was the first to successfully assemble an optical laser. In 1960 Maiman produced the ruby laser. In it a strobe lamp is coiled around the core, a rod of ruby that has mirrors at its ends, one of which is only partially solid. As the strobe light flashes it excites the ruby atoms that in turn emit photons. The photons are reflected back and forth by the mirrors until they pass through the partially solid mirror. This results in brief bursts of pure red laser light that was millions of times brighter than the sun. Maiman published his successful experiment but its importance was not realized immediately. Slowly other scientists began to build their own lasers and they quickly found out that materials other than ruby could be used as the core. In 1961, Ali Jaran produced a laser with helium-neon gas in a hollow tube at the core. This laser emitted continuous red laser light. In 1962 a laser was made with galliu arsenide (a kind of crystal). This laser proved to produce infrared light more efficiently. With many more experiment the laser was born. An ordinary light source produces many different wavelengths of light that go in many different directions (shown above). Where a laser is able to generate light waves of a single wavelength and all traveling along the same path (also shown above). This makes the light made from lasers extremely intense and pure in colour. DIFFERENT TYPES OF LASERS: Solid-State Lasers The most common solid laser media are rods of ruby crystals and neodymium-doped glasses and crystals. Solid-state lasers offer the highest power output. Gas Lasers The laser medium of a gas laser can be a pure gas, a mixture of gases, or even metal vapour, and is usually contained in a cylindrical glass or quartz tube. Two mirrors are located outside the ends of the tube to form the laser cavity. Semiconductor Lasers The most compact of lasers is the semiconductor laser which usually consists of a junction between layers of semiconductors with different electrical conducting properties. The laser cavity is confined to the junction region by means of two reflective boundaries. Liquid Lasers The most common liquid laser media are inorganic dyes contained in glass vessels. They are pumped by intense flash lamps in a pulse mode or by a gas laser in the CW mode. Free-Electron Lasers Lasers using beams of electrons that are unattached to atoms that are spiralling around magnetic field lines to produce laser radiation. These were first developed in 1977 and are now becoming important research instruments. They are tunable, as are dye lasers, and in theory a small number could cover the entire spectrum from infrared to X-rays. Free-electron lasers should also become capable of generating very high-power radiation, which is currently too expensive to produce. Laser Applications The use of lasers is wide spread and is now days becoming a commonly known tool. Lasers have become valuable tools in industry, scientific research, communication, medicine, military technology, and the arts. Lasers now days are used in operations for medicine, welding in industry and most commonly, as tools to point out objects (laser pointers).