Axial-Flow Laser

The simplest and most efficient of the gas lasers. An axial flow of gas is maintained through the tube to replace those gas molecules depleted by the electrical discharge used to excite the gas molecules to the lasing state. See Gas Discharge Laser.

Axis

Also Optical Axis.  The optical center-line for a lens system; the line passing through the centers of curvature of the optical surfaces of a lens.