Ruby laser

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The ruby laser was the first functional laser invented. Its inventor is Theodore H. "Ted" Maiman, who was, at the time, a Hughes Aircraft employee. On 16 May 1960, his ruby laser produced the first pulse of coherent light made by humans.

The ruby laser produces a pulse of visible light at a wavelength of 694.3 nm, which appears as deep red to human eyes. Typical ruby laser pulse lengths are on the order of a millisecond. These short pulses of red light are visible to the human eye, if the viewer carefully watches the target area where the pulse will fire.

Ruby lasers are rarely used today, being limited to specialized applications such as laser hair removal. Even there, they are being replaced by alexandrite lasers and Nd:YAG lasers.

[edit] Design

The ruby laser is a three level laser. The active laser medium (laser gain/amplification medium) is a synthetic ruby rod that is energized through optical pumping, typically by a xenon flash lamp. In early examples, the rod's ends had to be polished with great precision, such that the ends of the rod were flat to within a quarter of a wavelength of the output light, and parallel to each other within a few seconds of arc. The finely polished ends of the rod were silvered: one end completely, the other only partially. The rod with its reflective ends then acts as a Fabry-Pérot etalon (or a Gires-Tournois etalon). Modern lasers often instead use rods with ends cut and polished at Brewster's angle to avoid reflections, with external dielectric mirrors forming the optical cavity. Curved mirrors are typically used to reduce the alignment tolerances.