Photochemical Ignition Studies. 3. Ignition by Efficient and Resonant Multiphoton Photochemical Formation of Microplasmas
Final rept. Jun 1985-Mar 1986
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
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This is the third of a series of reports concerning the activation ignition of reactive gases using focused ultraviolet lasers. The goal of this research is to ascertain the potential of uv laser multiphoton photochemical ignition as a primary igniter or ignition augmentation source for propellants or their pyrolysis products. In this report, ignition properties of premixed H2O2 and H2N2O flows at atmospheric pressure have been studied. Tuning the laser in the 225.6 nm wavelength region has yielded three minima in the amount of incident laser energy ILE that is required to ignite either mixture. The minima correspond exactly to the two-photon resonant excitation wavelengths for the three spin-orbit split ground electronic states of oxygen atoms. A determination of the ILE necessary to ignite both premixed flows as a function of equivalence ration shows a minimum far into the fuel-lean region. Also, the minimum ILE value for the ignition of H2O2 was found to be around 0.3 mJ, while ignition of the same mixture with the green beam from a frequency doubled NdYAG laser 532 nm required an ILE value near 13 mJ. Additional time-resolved spectral studies were carried out on O2 and N2O flows alone. These indicated a resonant formation of a microplasma with a lifetime on the order of 100 nsec. All of these results lead to the conclusion that multiphoton photochemical ignition is a phenomenon consisting of three major components 1 the multiphoton photochemical formation of oxygen atoms 2 multiphoton focal volume 3 the formation of a laser microplasma using the electrons formed in the previous process as seed electrons.
- Physical Chemistry
- Lasers and Masers