Laser spectroscopic techniques for diagnosis of reactive plasmas

Summary form only given. Laser Induced Fluoresces (LIF) and laser cavity ring-down spectroscopy (CRDS) have been recently developed in our group for diagnosis of the active species (atoms, ions or radicals) in reactive plasmas. In the first experimental approach, time-resolved LIF technique was used to investigate the temporal evolutions of the number density of metastable state N₂ (A) in the nanosecond pulsed post discharge in a complicated H₂CO / N₂ /O₂ mixture. The N₂ (A, v=0) state was pumped to to N₂ (B, v=4) with a dye laser irradiation at 618 nm, and the subsequent fluorescence emission from N₂ (B, v=4) to N₂ (A, v=1) has been measured. The results indicated that the triplet meta stable state of N₂ (A) has played an important role in the removal mechanism of formaldehyde in the plasma. In the second experimental arrangement, CRDS has been applied to investigate the generation and destruction of NO₂ both in the air DBD discharge and nanosecond pulsed discharge plasmas. The observed oscillation of NO₂ number density during the post discharge will be presented and the results will be discussed in the conference.