Bloch equations and adiabatic rapid passage with radiation damping

Abstract

We present a new solution to the problem of an adiabatic rapid passage in a two-level spin system obeying the well-known Bloch equations supplemented by terms describing the radiation damping (coupling of the spin system with the resonant radio-frequency structure surrounding it). By a computer solution of a set of three nonlinear coupled differential equations we have shown that the previous quasisteady-state results of Bloom for an adiabatic rapid passage are not valid for strong radiation damping. Specifically, we have shown that under certain conditions the passage starts to be nonadiabatic, and very rapid radiative reversals of the macroscopic magnetization vector to its initial orientation, with respect to the strong external magnetic field, occur. These phenomena are very closely related to transient maser effects and to cooperative radiation emission from the so-called superradiant states of Dicke. We hope that this analysis will also help deepen the understanding of experiments on adiabatic rapid passage in highly polarized spin system in solids (polarized targets).