Chain reaction CW HF laser with stationary shock initiation
A new kind of chain reaction CW HF laser, initiated by atomic fluorine produced in the reaction NO + F2 yields FNO + F, has been developed. Uniform premixing of the reactant gases is achieved with negligible reactions in a cold supersonic stream, and combustion is initiated by a nearly-normal stationary shock. A small blowdown shock holder system was constructed to study the shock initiation laser scheme. A closed cavity stable resonator laser configuration was used in the shock holder, and HF laser action was confirmed by measurements of the IR cavity intensity and by mirror calorimetry. Optimum performance was achieved in a mixture of 13.7% F2, 2.7% H2, and 5.4% NO, in helium diluent, with a shock holder pressure of 13 Torr. The optical axis (mirror co-normal) was located approximately 3.3 cm downstream from the normal shock. A total out-coupled energy of 41 J over a lasing duration of 0.75 s was measured, corresponding to 55 W average power. A lasing zone at least 3.4 cm in length was indicated, with peak cavity intensity of approximately 100 W/sq cm. The chemical efficiency for these conditions was conservatively estimated to be 1%.