A helium-neon (henceforth abbreviated HeNe) laser is basically a fancy neon sign with mirrors at both ends. Well, not quite, but really not much more than this at first glance (though the design and manufacturing issues which must be dealt with to achieve the desired beam characteristics, power output, stability, and life span, are non-trivial). The gas fill is a mixture of helium and neon gas at low pressure. A pair of mirrors - one totally reflective (called the High Reflector or HR), the other partially reflective (called the Output Coupler or OC) at the wavelength of the laser's output - complete the resonator assembly. This is called a Fabry-Perot cavity (if you want to impress your friends). The mirrors may be internal (common on small and inexpensive tubes) or external (on precision high priced lab quality lasers). Electrodes sealed into the tube allow for the passage of high voltage DC current to excite the discharge.
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Introduction
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Safety
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Theory
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Mirrors
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Wavelenghts
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Demonstration
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More about lasers
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