  In this paper we consider two problems in diagnostics of trapped ion crystals
in which an analysis of the ions' collective oscillatory motion yield
potentially useful results. When one of the ions in a linear crystal undergoes
a collision, observation of the subsequent motion allows one to deduce the
identity of which ion sustained the collision. When a linear ion crystal is
formed with a dark impurity ion, analysis of the ions' motion can identify the
mass (and thus give an important clue to the species) of the impurity.

Quantum Physics;Atomic Physics;Optics