We present a new formalism for the description of multiphoton plasmon
excitation processes in jellium clusters. By using our method, we demonstrate
that, in addition to dipole plasmon excitations, the multipole plasmons
(quadrupole, octupole, etc) can be excited in a cluster by multiphoton
absorption processes, which results in a significant difference between plasmon
resonance profiles in the cross sections for multiphoton as compared to
single-photon absorption. We calculate the cross sections for multiphoton
absorption and analyse the balance between the surface and volume plasmon
contributions to multipole plasmons.Comment: 29 pages, 1 figur