Inverse bremsstrahlung

Collisional absorption of electromagnetic wave energy by charged particles scattering from other charges. In a weakly collisional unmagnetized Drude model, with $X={\omega }_p^2/{\omega }^2<1$, the intensity absorption coefficient is ${\alpha }_I\simeq ({\nu }_{ei}/c)X/\sqrt{1-X}$. The corresponding electric-field amplitude decays at half that rate.