  A simple minimally perturbative method is introduced which provides the
ability to experimentally measure both the radial confining potential and the
interaction potential between two individual dust particles, levitated in the
sheath of a radio-frequency (RF) argon discharge. In this technique, a single
dust particle is dropped into the plasma sheath to interact with a second
individual dust particle already situated at the system's equilibrium point,
without introducing any external perturbation. The resulting data is analyzed
using a method employing a polynomial fit to the particle displacement(s),
X(t), to reduce uncertainty in calculation. Employing this technique, the
horizontal confinement is shown to be parabolic over a wide range of pressures
and displacements from the equilibrium point. The interaction potential is also
measured and shown to be well-described by a screened Coulomb potential and to
decrease with increasing pressure. Finally, the charge on the particle and the
effective dust screening distance are calculated. It is shown for the first
time experimentally that the charge on a particle in the sheath of an RF plasma
decreases with increasing pressure, in agreement with theoretical predictions.
The screening distance also decreases with increasing pressure as expected.
This technique can be used for rapid determination of particle parameters in
dusty plasma.
