GAS LASER

A rod made of an insulating material having a thermal coefficient of expansion in the range from +1 to -1 part in 107 per degree centigrade is mounted between a pair of mirrors and hermetically sealed either within a glass or a stainless steel enclosure containing a gas discharge medium. The stainless steel enclosure may be clamped to and fixedly spaced from the rod by projections formed on the enclosure and symmetrically disposed around the rod toward the ends of the rod. The mirrors and an annular piezoelectric disc positioned within the enclosure between one of the mirrors and one end of the rod are axially mechanically biased against the ends of the rod either by a spring loading structure or by a gas pressure differential. An anode and an annular cathode electrically insulated from one another for operation at different potentials are mounted toward the opposite ends of the rod. A discharge path communicating with the gas discharge medium and including a portion of a bore axially extending through the rod is provided in the rod between and in communication with the anode and the cathode to provide a gas discharge for excitation of the gas discharge medium to produce a laser beam. This discharge path may be placed in a magnetic field having a component in the direction of the laser beam to Zeeman split the atomic transition line at which the laser action occurs so that the laser oscillates at two different frequencies and thereby produces an output beam with two components of different frequency and polarization. In response to a portion of the laser beam a feedback control circuit changes the thickness of the piezoelectric disc to maintain the spacing between the mirrors as required, for example, to stabilize the frequency, or frequencies, of oscillation of the laser at or in a known relationship to the center of the atomic transition line at which the laser action occurs.