On the origin of type III fundamental

A two-component scheme for the generation of type III fundamental radiation is proposed. The first component of the fundamental arises at a plasma level omega sub(L) [perspective to] omega sub(t) because of the Rayleigh scattering of the plasma waves into electromagnetic radiation. The other component arises at omega ' sub(L) [perspective to] omega sub(t) /2 because of the decay of the first component into plasma waves and the subsequent rescattering of the plasma waves into electromagnetic radiation omega sub(t) [perspective to] 2( omega sub(t) /2). By its properties (location, directivity, polarization), the second component is essentially the same as the second harmonic radiation produced by a stream of fast electrons at omega ' sub(L) [perspective to] ( omega sub(t) /2). This scheme is used to solve the main problems (localization and directivity of the source, polarization of type III fundamental) of the harmonic theory of type III solar bursts.