Fig.1. Construction of He-Ne laser

The first such 1аsег was built in I960 at Bеll Telephone Laboratories. It consists of a discharge tube 100 cm long with an inside diameter of 1,5 cm filled with helium at 1 torr pressure and with neon at 0.1 torr. Flat reflector plates, which must be adjusted parallel within a few seconds of arc, are included in the gas filled section of the tube.

A simplified diagram of this laser is given in Fig.1.

The power required to excite the laser action is in the tens-of-watts range. The output роwer is in the 1/100-th watt range. At this level of operation, the tube is so cool that it can be held in the hand without discomfort.

Thе great value of helium-neon lasers is their remarkable monochromaticity and stability under carefully controlled experimental conditions.

To communication engineers such a continuously operating source is an important device.