The possibility of nonlinear capture of a Langmuir wave into the region of weak inhomogeneity under parametric interaction with a strong electromagnetic wave is shown. Under overcritical conditions in the presence of dissipation, spatio-temporal amplitude correlations occur and then, wave soliton structures are formed. In such a system, powerful regular oscillations appear. This leads to giant modulation of the pump pulse. Under further increasing of overcriticity, the influence of Langmuir instability becomes more essential, and, as a result, solitary waves become sharply amplified and compressed.