Backscattering amplification of laser radiation in a medium with fluctuations of the imaginary part of permittivity

The effect of backscattering amplification of laser radiation with respect to the radiation intensity reflected from an ordinary mirror in a medium with fluctuations of the real (refractive index) and the imaginary (absorption or amplification coefficient) parts of the permittivity is considered. Formulas for the backscattering amplification coefficient and the variance of the intensity fluctuations of the reflected wave propagating in a random dissipative (amplifying) medium are derived. Asymptotic expressions derived for the saturation region of intensity fluctuations take into account the effect of fluctuations of the refractive index and absorption (amplification) coefficient, as well as their correlation. The contribution of fluctuations of the complex permittivity parts and the characteristic spatial scale of the problem to the backscattering amplification coefficient is analysed. It is shown that for uncorrelated fluctuations of the real and imaginary parts of the permittivity of a random medium, the backscattering amplification coefficient in the region of strong fluctuations is larger than in a transparent random medium. It is also found that the correlation of pulsations of the real and imaginary parts of the permittivity suppresses the backscattering amplification effect in an absorbing medium and increases this effect in an amplifying medium.