A continuous wave laser based on the electronic I*(.sup.2P.sub.1/2)-I(.sup.2P.sub. 3/2) transition of atomic iodine at 1.315 microns from the NCl(a.sup.1.DELTA.)+I(.sup.2P.sub. 3/2) energy transfer reaction using a transverse flow device having gas flow from an upstream subsonic combustor section through a converging-diverging supersonic slit nozzle to a downstream supersonic section and an intersecting optical resonator. Laser operation is achieved through the transformation of the gas phase chemical reagents, D.sub.2 (deuterium), F.sub.2 (fluorine), NF.sub.3 (nitrogen trifluoride), DCl (deuterium chloride) HI (hydrogen iodide) in the subsonic section and HN.sub.3 (hydrogen azide) in the supersonic section.