Multiphoton photochemistry and resonant laser ignition of reactive gases

The primary goal of this work is to determine what fraction of the incident laser energy (ILE) that drives the formation of the microplasma and ignition is absorbed in the ignition event. The fraction of energy absorbed is the minimum ignition energy under these experimental conditions. Although a distinct wavelength dependence on the ILE required for ignition was observed in our past work, an additional motivation of this work is to ascertain that if once a minimum ignition energy has been deposited is there a selective enhancement in ignition which is wavelength dependent. A tunable laser system which operates in the ultraviolet (UV) has been utilized to ignite premixed reactive gaseous flows of H₂/O₂, D₂/O₂ and CH₄/N₂O in a jet burner at atmospheric pressure. Multiphoton UV photodissociation of the fuel or oxidizer molecules produced ground state radicals (H and 0 atoms). Resonance enhanced multiphoton excitation and ionization of these radicals formed a laser-produced microplasma which served as an ignition source