On some properties of the scattering amplitude

The paper presents a number of useful definitions and properties of the scattering amplitude as an analytical function of spherical coordinates. The scattering amplitude is considered in a composite incident field. It has been shown that, in calculating the scattering field in the wave zone, scattering amplitudes going beyond the visible range can be neglected. The results of this work can be used in calculating radiation pressure in case of irregular external field.