We carry a variety of new-surplus and overstock Helium-Neon laser heads, tubes, and power supplies. All at a fraction of the normal cost. Select a link below.

History:
The first successful operation of a continuous wave helium neon laser was observed by Javan, Bennett, and Herriott at Bell Labs in 1962.  The helium neon laser uses a low pressure mixture of helium and neon gases. The mixture is predominantly helium with only 10% neon.

Cavity Type:
Most commercial helium neon lasers use a quasi-hemispherical cavity configuration, where a plane mirror is placed just short of the center of curvature of a concave spherical mirror.  The disadvantage of this cavity configuration is that it only utilizes about one-third of the available plasma volume in the cavity. This limitation in power is more than outweighed by its ease of adjustment and stability once aligned.

Longitudinal Modes:
Because of the rapid motion of atoms or molecules in the laser plasma tube, a gas laser transition does not consist of a sharp line. The Doppler effect causes it to broaden to a smooth Gaussian profile. A Doppler broadened line has a width dependent on the velocity of the atoms (temperature) and the wavelength of the transition. Red HeNe lasers typically have a full-width-half-max (FWHM) of about 1,400Mhz. Superimposed on the Doppler broadened gain curve is the cavity resonance function. For a 0.5 meter cavity, the mode spacing is 300Mhz. The sharpness of these modes is a function of the multipass nature of the cavity and is typically about 1Mhz. For such a cavity, laser output therefore consists of five or six single sharp frequencies (FWHM = approx. 1Mhz) separated by 300Mhz. The relative intensity of the cavity modes is defined by the Doppler broadened gain curve. In a very short cavity (less than 0.15 meter), only one mode will exist and the laser output will then consist of a single frequency.

Mode Sweeping / Mode Hopping:
The multiple longitudinal mode structure described above, of all but the shortest helium neon laser cavities (less than 6 inches) causes a power fluctuation phenomenon termed mode sweeping or mode hopping. The overall amplitude fluctuations are typically a few percent.

Hard Seals:
Melles Griot helium neon lasers are sealed with a truly zero-leak hard-seal. A special preformed ring of the frit sealing material is placed around the parts during initial assembly. Both the cathode retaining end-cap and the anode tube are manufactured of Kovar (a nickel/iron/cobalt alloy which is thermally compatible with the hard borosilicate glass).Using radio frequency induction heating techniques, the Kovar cathode and end-cap are welded to the plasma tube envelope. Both cavity mirrors are welded to the plasma envelope. The preformed frit material flows fully onto both parts creating a proven and reliable seal. This use of glass-metal seals throughout the tube and the complete absence of epoxy bonds results in the elimination of tube leakage. The overall volume of the plasma tube provides a sufficient gas reservoir so that the gas mixture in the plasma tube is invariant with time and is precisely known. The result is reliable, consistent operation and a long shelf life.

Helium Neon Lasers

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