A longitudinal-flow modular CO2 laser having at least one CW output power has metallic end-flange devices at the two ends of the laser and a metallic intermediate-flange device at the transition from one laser module to another laser module. The flange devices have flank-sides and end-faces with mounting bores. A plurality of dielectric individual tubes are provided between the flange devices. The dielectric individual tubes have end regions mounted in the end-face mounting bores of the metallic flange devices. Flank-side gas inlet and outlet connections are provided at the flange devices. A large volume chamber is provided permitting gas flow between the mounting bores and the gas connections. The chamber connects two of the mounting bores and is disposed within at least one of the end-flange and intermediate-flange devices.
