  We report a numerical investigation of surface plasmon (SP) propagation in
ordered and disordered linear chains of metal nanospheres. In our simulations,
SPs are excited at one end of a chain by a near-field tip. We then find
numerically the SP amplitude as a function of propagation distance. Two types
of SPs are discovered. The first SP, which we call the ordinary or quasistatic,
is mediated by short-range, near-field electromagnetic interaction in the
chain. This excitation is strongly affected by Ohmic losses in the metal and by
disorder in the chain. These two effects result in spatial decay of the
quasistatic SP by means of absorptive and radiative losses, respectively. The
second SP is mediated by longer range, far-field interaction of nanospheres. We
refer to this SP as the extraordinary or non-quasistatic. The non-quasistatic
SP can not be effectively excited by a near-field probe due to the small
integral weight of the associated spectral line. Because of that, at small
propagation distances, this SP is dominated by the quasistatic SP. However, the
non-quasistatic SP is affected by Ohmic and radiative losses to a much smaller
extent than the quasistatic one. Because of that, the non-quasistatic SP
becomes dominant sufficiently far from the exciting tip and can propagate with
little further losses of energy to remarkable distances. The unique physical
properties of the non-quasistatic SP can be utilized in all-optical integrated
photonic systems.
