The probability distribution of a two-level ion confined in a harmonic
trap and perturbed by the absorption and emission of photons is calcu
lated. The ion is assumed to be excited by a light beam and relaxes ba
ck either by induced emissions or irreversible spontaneous emissions.
The photon-ion interaction is modeled as a perturbing noise acting on
the ion by modifying its energy and momentum. The current calculations
reproduce the quantum results of the laser cooling of ions in static
traps in the heavy particle limit.