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The helium neon laser(HeNe laser) is a discharge pumped gas laser. It consists of a glass tube filed with a low pressure mix of helium and neon. There are also electrodes in the tube and a mirror in each end. One of the mirrors is only partialy reflective, and will let some of the light at the laser output frequency, through. To use the laser a high voltage (about 1000VDC) is connected to the electrodes and a starting pulse(10000V+) is administred. This causes the neon to emit photons. Some of the photons will be reflected by the mirrors. These photons will hit the gas atoms and cause further emission, And thus more light. This process creates light with in narrow frequency band, and with high coherence(this means that the light waves move in phase).

This laser type were used in laser printers, laserdisc players and barcode scanners but has been replaced by the cheaper, more power efficient and much smaler laser diode. But is still used in applications like interferometers and holography where the higher coherence is wanted. The HeNe laser is easily recognized due to a more orange(a wavelength of about 632.8 nano meters) light than the laser diode. HeNe lasers commonly has an output of between 0.5mW and 5mW, but larger laboratory lasers may have up to about 0.3W.

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