A multi-chord fiber-coupled interferometer [Merritt et al., Rev. Sci.
Instrum. 83, 033506 (2012)] is being used to make time-resolved density
measurements of supersonic argon plasma jets on the Plasma Liner Experiment
[Hsu et al., Bull. Amer. Phys. Soc. 56, 307 (2011)]. The long coherence length
of the laser (>10 m) allows signal and reference path lengths to be mismatched
by many meters without signal degradation, making for a greatly simplified
optical layout. Measured interferometry phase shifts are consistent with a
partially ionized plasma in which an initially positive phase shift becomes
negative when the ionization fraction drops below a certain threshold. In this
case, both free electrons and bound electrons in ions and neutral atoms
contribute to the index of refraction. This paper illustrates how the
interferometry data, aided by numerical modeling, are used to derive total jet
density, jet propagation velocity (~15-50 km/s), jet length (~20-100 cm), and
3D expansion.Comment: 6 pages, 4 figures, invited paper at the 19th High Temperature Plasma
Diagnostics Conference, Monterey, CA, May 6--10, 201