Damping properties of surface polaritons in a thin crystal slab

A formula for the frequency-dependent damping rate of long-wavelength surface polaritons in a crystal slab with small intrinsic damping is derived and analysed. Special attention is paid to the dependence of the damping upon the thickness of the slab. It is shown that surface polaritons in thin dielectric slabs at frequencies slightly higher than the TO phonon frequency have lifetimes which are several orders of magnitude longer than the lifetimes of surface polaritons in a semi-infinite dielectric. Their propagation length along the surfaces of an ideally flat slab is a few tens of metres. Similar conclusions also apply to low-frequency (infrared) surface polaritons in a thin metallic slab.