The ultimate absorption at light scattering by a single obstacle

Based on fundamental properties of light scattering by a particle we reveal the existence of the ultimate upper limit for the light absorption by any partial mode. First, we obtain this result for scattering of a plane wave by a symmetric spherical or infinite cylindrical structure of an arbitrary radius. Then, we generalize it to an arbitrary finite obstacle. Importantly, the result is true for any polarization, any angle of incidence of the plane wave and any type of the structure (homogeneous, stratified, or with smoothly variable refractive index). The corresponding maximal partial cross- section is a universal quantity, which does not depend on the optical constants of the scatterer its radius, and even its shape.