Meromorphic susceptibility is a material parameter that appears usually in pump - probe experiments, where so-called degenerate susceptibilities, as a function of angular frequency, describe the radiation and material interaction. Kramers - Kronig dispersion relations are invalid for meromorphic susceptibilities. Phase retrieval by the maximum-entropy model from the modulus of total susceptibility, with poles and zeros in the complex plane, is considered. Complex analysis is employed in the description of the nature of the meromorphic total susceptibility.