created by Kenneth Howard
Device for producing a narrow beam of light, capable of travelling over vast distances without dispersion, and of being focused to give enormous power densities (108 watts per cm2 for high-energy lasers). The laser operates on a principle similar to that of the maser (a high-frequency microwave amplifier or oscillator). The uses of lasers include communications (a laser beam can carry much more information than can radio waves), cutting, drilling, welding, satellite tracking, medical and biological research, and surgery. Sound wave vibrations from the window glass of a room can be picked up by a reflected laser beam. Lasers are also used as entertainment in theatres, concerts, and light shows.
Laser materialAny substance in which the majority of atoms or molecules can be put into an excited energy state can be used as laser material. Many solid, liquid, and gaseous substances have been used, including synthetic ruby crystal (used for the first extraction of laser light in 1960, and giving a high-power pulsed output) and a helium–neon gas mixture, capable of continuous operation, but at a lower power. A silicon-based laser was created in 2004, using the natural atomic vibrations of silicon nanocrystals to generate the light.
Helium–neon lasersThe helium–neon laser is the commonest and cheapest kind; it consists of a sealed glass tube containing a mixture of helium and neon gases at low pressure and with mirrors sealed onto the tube at either end. An electrical discharge is passed through the tube from two sealed-in electrodes. The energy of the discharge ‘pumps’ the neon atoms, and photons of wavelength 0.6328 × 10−6 m are emitted (red light). The light bounces between the mirrors and is amplified at each pass. One of the mirrors is slightly transparent to allow the pencil beam of red light to emerge.