Аннотация:Excitation of guided electromagnetic waves in thin films with periodic surface inhomogeneities is studied. It is theoretically shown that at certain conditions the intensity of the excited mode in the ideal thin film without absorption tends to infinity when the corrugation depth tends to zero. This effect can be interpreted as a resonance phenomena in ideal resonator which merit factor is inversely proportional to the corrugation depth. The results of the calculations based on the numerically explicit solution of the two-dimensional model problem support the above theoretical prediction. The main conclusion of the study is that even small inhomogeneities may cause an excitation of guided modes in thin films and considerable enhancement of the electric field.