  The question of suitability of transfer matrix description of electrons
traversing grating-type dielectric laser acceleration (DLA) structures is
addressed. It is shown that although matrix considerations lead to interesting
insights, the basic transfer properties of DLA cells cannot be described by a
matrix. A more general notion of a transfer function is shown to be a simple
and useful tool for formulating problems of particle dynamics in DLA. As an
example, a focusing structure is proposed which works simultaneously for all
electron phases.
