Using laser-induced fluorescence (LIF) the ion density near the edge o
f an expanding plasma sheath has been measured. These measurements uti
lized a transition of N2+ [the P12 component of the X2SIGMA(g)+(nu = 0
) double-line arrow pointing right B2SIGMA(u)+(upsilon = 0) band] in a
N2 plasma. The strength of the laser-induced fluorescence was used as
a measure of the temporally and spatially varying ion density. The ex
panding sheath was produced by applying a -5 kV pulse to a polished pl
anar electrode in the plasma source ion implantation device [J. R. Con
rad et al., J. Vac. Sci. Technol. A 8, 3146 (1990)]. The laser beam wa
s aligned normal to the surface and was reflected off the center of th
e electrode. The LIF diagnostic used here is nonperturbing whereas pre
vious researchers have used Langmuir probes, which perturb the plasma,
to make their measurements. As such, the data reported here represent
a benchmark measurement of pulsed sheaths and allow a better comparis
on between experimental measurements and theoretical predictions. It h
as been found that the sheath edge moves approximately 16 times faster
than the ion-acoustic velocity during the early par-t of the pulse, t
< 1 mus, and then slows to approximately the ion-acoustic velocity af
ter 6 mus. In addition to the LIF measurements, a biased probe was use
d far from the cathode to determine the sheath edge location. Good agr
eement is found when the LIF and probe data are compared. The LIF data
also are compared to the predictions of a simulation that is based on
a time-varying two-fluid model of the sheath [G. A. Emmert and M. A.
Henry, J. Appl. Phys. 71, 113 (1992)]. While the predictions of the mo
del show moderate agreement with the data, substantial discrepancies a
re observed. These discrepancies are attributed to a number of physica
l phenomena that are not included in the present model.