It is shown, that the pace of wave instability development is extremely reducing in the quasilinear stage. That stage realizes when the system has exceeded the instability threshold slightly and integrated intensity of the high-frequency oscillations (independently of the spectrum width) runs up to the bounded above value. The coherently locked (by pumping) phases of unstable modes can form the induced interference outburst. The amplitude of the outburst is proportionate to the width of instability spectrum and can reach the large value. The dynamics of discrete (the laser pulses formation) and continuous (the modulation instability of intensive monochromatic wave) instability spectra have been discussed. In the first case one could look the fine structure formation of laser pulse with great number of radiation burst. In the second case is realized a single outburst of the wave modulation. The several wave-length are placed within the range of such outburst. The width of the instability spectra are reduced with time, the systems right up to line spectrum formations and interference effects are weakened.