A CO2 gas laser in which the mixture of gases flows slowly in a direction parallel to the optical axis. The interaction of these gases generates heat and contaminating byproducts like carbon monoxide. A vacuum pump and gas input work in tandem to remove the byproducts and replenish the gas in the laser tube. Hot gas molecules strike and transfer their heat energy to the walls of the laser tube, which is cooled by air, oil, or water. These lasers can produce about 60 watts of power for every meter of tube length. Practically, this is restricted to about 3 meters and 180 watts overall.