Rotational Relaxation of NO in Seeded, Pulsed Nozzle Beams
In the last few years pulsed nozzle beams became an important experimental tool in spectroscopy, especially in connection with the development of pulsed high power lasers. High momentary intensity at moderate pumping speed, good cooling and control of dimerisation by large nozzles are only some of the important advantages. Several different designs for pulsed valves have been realized to produce short gas pulses in the submillisecond range1–3, but still little is known about hydrodynamic properties of these beams. They do depend on the details of the design, and it is known today that ultrashort gas pulses do not give good nozzle beams1. Theoretical estimates have been made about the time that is necessary to come to a stationary behaviour of the expansion4. We want to present a method that gives some insight into the dynamics of these beams. We study in detail the features of the pulsed valve designed by Smalley2 by looking with LIF at the rotational relaxation of NO in very dilute mixtures with He and Ar. LIF is an ideal probe because the molecules can be detected without any interference with the beam.
KeywordsRotational State Rotational Temperature Rotational Relaxation Pulse Valve Pulse High Power Laser
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