A remote plasma generator, coupling microwave frequency energy to a gas and delivering radicals to a downstream process chamber, includes several features which, in conjunction, enable highly efficient radical generation. In the illustrated embodiments, more efficient delivery of oxygen and fluorine radicals translates to more rapid photoresist etch or ash rates. A single-crystal, one-piece sapphire applicator and transport tube minimizes recombination of radicals in route to the process chamber and includes a bend to avoid direct line of sight from the glow discharge to the downstream process chamber. Microwave transparent cooling fluid within a cooling jacket around the applicator enables high power, high temperature plasma production. Additionally, dynamic impedance matching via a sliding short at the terminus of the microwave cavity reduces power loss through reflected energy. At the same time, a low profile microwave trap produces a more dense plasma to increase radical production. In one embodiment, fluorine and oxygen radicals are separately generated and mixed just upstream of the process chamber, enabling individually optimized radical generation of the two species.