Abstract: A laser combustor apparatus for a chemical laser including an injector and transition manifold wherein the injector has a barrier area located between the oxidizer plenum and fuel plenum and a coolant area is located between the fuel plenum and a porous injector face plate, said barrier area and coolant area being connected by a restricted passage to control the pressure in the barrier area maintaining it higher than that in the oxidizer or fuel plenum. The combustor and manifold form a T-shape and have a liner fixed therein with a spaced relationship into which a diluent is placed for a purge thereof to keep combustion products from getting behind the liner.