The gain medium of the laser, as suggested by its name, is a mixture of helium and neon gases, in a 5:1 to 20:1 ratio, contained at low pressure He at 1 torr and Ne at 0.1torr (an average 50 pascal unit (Pa) per cm of cavity length) in a glass envelope. The energy or pump source of the laser is provided by an high voltage electrical discharge through an anode and cathode at each end of the glass tube. A current of 5 to 100 mA is typical for Continuous wave (CW) operation. The optical cavity of the laser typically consists of a plane, high-reflecting mirror at one end of the laser tube, and a concave output coupler mirror of approximately 1% transmission at the other end.