  We report one-dimensional pinning of a single ion by an optical lattice. The
lattice potential is produced by a standing-wave cavity along the rf-field-free
axis of a linear Paul trap. The ion's localization is detected by measuring its
fluorescence when excited by standing-wave fields with the same period, but
different spatial phases. The experiments agree with an analytical model of the
localization process, which we test against numerical simulations. For the best
localization achieved, the ion's average coupling to the cavity field is
enhanced from 50% to 81(3)% of its maximum possible value, and we infer that
the ion is bound in a lattice well with over 97% probability.
