Gas dynamic quantities within an underexpanded nitrogen free jet, seeded 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 adjacent rotational lines in the NO gamma band near 225 nm at a rate of 4 kHz. Spatially resolved excitation scans were obtained by monitoring the induced broadband fluoresence. Modeling the Doppler-shifted excitation scans with Voigt profiles permitted simultaneous determinations of NO velocity, rotational temperature, and pressure. Zero Doppler shift was referenced to an absorption trace obtained across a static cell and recorded concurrently with the excitation scan. Typically, the measured and predicted axial distributions agreed within 10%. At high Mach numbers there was evidence of rotational freezing of NO.
© 1993 Optical Society of America
Michael D. Di Rosa, Albert Y. Chang, and Ronald K. Hanson, "Continuous wave dye-laser technique for simultaneous, spatially resolved measurements of temperature, pressure, and velocity of NO in an underexpanded free jet," Appl. Opt. 32, 4074-4087 (1993)