Development of a Two-dimentional Measurement System for Supersonic Flow using LIUVF

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Oxygen molecules have the absorption bands in the broad range from 114 in the ultra violet to 1580 nm in the infrared. The dominant Schumann-Runge absorption band system corresponds to the transition of the ground state X^3SIGMA_g^- to the excited state B^3SIGMA_u^-, and has the discrete absorption bands from 175 to 250 nm and the continuum ones from 130 to 175 nm. The B state has been known to be crossed by many repulsive potential curves and to be predissociated. Since the strong predissociation rate makes the lifetime of the fluorescence short in the order of 10^<-12> seconds, it is possible to assume that the fluorescence yields prior to the intermolecular collision.In this study, we investigate the capability of imaging of rarefied gas flow using O_2-LIPF (Laser-Induced Predissociative Fluorescence). Since oxygen is one of main component of air, O_2-LIPF may make it possible to visualize the air flow in the high speed wind tunnel without the tracer. However, because the visualization of the flow field below the room temperature using O_2-LIPF is very difficult, is has been applied only to the high entalpy and combustion flow^<(1)>, not to high speed flow with low temperature. In this study, the rarefied oxygen flow is visualized by O_2-LIPF, using an ArF excimer laser (193 nm) and a high-sensitive CCD camera. If long exposure time (1200 seconds) of the CCD camera is set and the scattered laser beam is suppressed sufficiently, the oxygen flow below the room temperature using O_2-LIPF can be imaged successfully.