CONTINUOUS-WAVE DYE-LASER TECHNIQUE FOR SIMULTANEOUS, SPATIALLY-RESOLVED MEASUREMENTS OF TEMPERATURE, PRESSURE, AND VELOCITY OF NO IN AN UNDEREXPANDED FREE JET

Gas dynamic quantities within an underexpanded nitrogen free jet, seed ed with 0.5% NO, were measured nonintrusively by using an intracavity- doubled, rapid-tuning, cw ring dye laser. The UV beam passed obliquely through the jet axis, and its frequency repetitively scanned across a djacent rotational lines in the NO gamma band near 225 nm at a rate of 4 kHz. Spatially resolved excitation scans were obtained by monitorin g the induced broadband fluoresence. Modeling the Doppler-shifted exci tation scans with Voigt profiles permitted simultaneous determinations of NO velocity, rotational temperature, and pressure. Zero Doppler sh ift was referenced to an absorption trace obtained across a static cel l and recorded concurrently with the excitation scan. Typically, the m easured and predicted axial distributions agreed within 10%. At high M ach numbers there was evidence of rotational freezing of NO.