▎ 摘　　要

We considered the scattering and absorption of the H and E-polarized plane waves by an infinite flat graphene strip grating placed in a dielectric slab, in the THzrange. Accurate numerical treatment was based on the singular integral equations and their projection to specially tailored orthogonal polynomials. The resulting numerical algorithm possessed guaranteed convergence and provided controlled accuracy. Reflectance, transmittance, and absorbance were studied, and the resonances on the surface-plasmon modes, the grating modes, and the slab modes were identified. The grating or lattice modes are caused by the periodicity. Their complex frequencies are extremely close to Rayleigh anomalies and therefore the Q-factors are extraordinarily high, which makes them promising in various applications.