Complex resonance in Fresnel reflection of radiation pulses

The Fresnel reflection of radiation pulses with an exponential temporal amplitude profile is analyzed. The conditions for the relevance of the concept of reflectance at a complex frequency, the imaginary part of which determined the rate of time variation of the amplitude, are specified. For the radiation pulses under study, we demonstrate a complex resonance, i.e., an increase in the magnitude of reflectance for the complex frequency of incident radiation (trailing edge of a pulse) that approaches the complex frequency of natural oscillations of oscillators in the medium.