Modulation instability of light beams and pulses propagating in absorbing media

The development of modulation instability of light beams and pulses propagating in an absorbing medium is analyzed. Based on the proposed approach, the domain of increasing perturbations is estimated more exactly. It is shown that, compared to the traditional approach, this domain can be enlarged by 20–50% in frequency and by 50% in the gain increment. For femtosecond pulses, the analysis of the modulation instability is carried out both on the basis of the well-known Schrödinger equation with the time derivative of nonlinear response of the medium and by using the original method of its transformation. It is shown that in the latter case, the nonlinearity dispersion increases the interval of frequencies for which the modulation instability is developed. This more adequate description of the development of the modulation instability in an absorbing medium allowed us to obtain more accurately the frequency intervals of its realization compared to the data available in the literature.