MEASURING THE VELOCITY DISTRIBUTION OF MOLECULES IN GAS-DYNAMIC BEAMS BY LASER FLUORESCENCE

A procedure for measuring the velocity distribution of molecules in a rarefied gas beam is described. Molecules are excited to a fluorescence state and the velocity at which the excited ''cloud' spreads is measured. The main advantages of the procedure are: the possibility to investigate short (submillimeter) gas pulses, the absence of perturbations acting on the beam, and the possibility of a quasi-local measurement of the distribution function. We measured the beam velocity and distribution of longitudinal velocities (temperature) for various phases of a 250-musec gas pulse. Mixtures of Ne and Ar with SO2 as the fluorescing component were used. The flight base was almost-equal-to 8 mm in our measurements.