Visualization of supersonic flow using O2-LIPF (2nd report, improvement of a detection system and analysis of detection signal)

This paper describes the O2-LIPF (laser-induced predissociative fluorescence) method for visualization of high-speed flows. Under the condition of weak laser excitation, the linear dependence of O2-LIPF both on number density of oxygen molecules and on laser intensity is presented theoretically and verified experimentally using a static condition. The vibrational and rotational temperature distributions along a centerline of a supersonic free jet are calculated theoretically, leading to the theoretical fluorescence signal distribution. To improve the S/N ratio of a detection system including an image intensifier and a high-sensitivity CCD camera, three spectral filters are selected to eliminate the scattered laser beam, and three images visualized through them are compared. A low-speed oxygen flow is also successfully visualized using O2-LIPF.