Electromagnetic emission by subsequent processes L->L'+S and L+L'->T

Using a 2.5-D electromagnetic particle-in-cell (PIC) model, very early stages of a generation of the electromagnetic emission produced by a monochromatic Langmuir wave are studied. It is found that the electromagnetic emission, which is dominant on the harmonic of the plasma frequency, starts to be generated in a very small region of k-vectors. Later on the k-vectors of this emission are scattered around a `circle' (in our 2-D case), given by the relations for the L+L'->T process. Analytical analysis of two subsequent processes L->L'+S a L+L'->T confirms these results.