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When most people see a laser beam they are amazed by its unique physical properties. Laser light is so unique from other light because it is coherent; unlike ordinary light, which travels in all directions, laser light travels in a straight beam. The word laser is an acronym for Light Amplification by Stimulated
Emission of Radiation. The history of the laser is very interesting. Lasers have changed immensely since they were first invented. Before the laser was invented, Charles Townes developed the maser in
1954. The maser has basically the same principles as the laser, but it involves microwaves instead of light. The maser lead Theodore Maximan to assemble the first working laser in 1960; he did this by applying the masers qualities to light. This first solid-state laser was a ruby crystal laser. A year after the first solid-state laser was invented, the first gas laser was constructed by Ali Javan,
W. R. Bennett, and D. R. Herriot. This was a helium-neon laser. The helium-neon laser is the most common laser found today. Many other types of lasers have been invented since then: the semiconductor laser (1962), the chemical laser
(1964), the liquid laser (1966), and the free electron laser (1977). All lasers work basically on the same principles. First the atoms in the substance used are pumped. For example, the helium and neon would be pumped in a helium-neon laser. This is where the electrons of the atoms jump to higher orbitals, which have more energy. The substance can be pumped by using flashlamps, other lasers, atomic explosions, electric discharges, solar energy, and etc... When the atoms are pumped, they perform stimulated emission. This is where the electrons are stimulated by photons to release coherent photons of a single frequency and color. After the pumping process, the oscillation process takes place. In this process energy is amplified to make it stronger and more useful. This is done by bouncing the photons between two mirrors until they reach a certain intensity. The two mirrors are one of 100 percent efficiency and one of a lesser efficiency.
When the photons reach the certain intensity, they leave the mirror of lesser efficiency in a coherent beam. There are basically four main types of lasers: solid-state, gas, liquid, and semi-conductor.
Solid-state lasers are made from a crystalline material such as ruby. The crystals have impurities in them that can be stimulated to release radiation in a coherent fashion. These impurities are needed to make the laser last for long periods of time. If the crystals do not have impurities, then they can have some added; this is called "doping." The crystals in solid state lasers are usually pumped by using flashlamps. Gas laser beams are much more

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