Phase-sensitive observables as a route to understanding molecular continua

Abstract

We consider the origin and implications of the phase lag, an observable in two-pathway excitation schemes whose recent measurement raised both interest and controversy. A closed-form expression is derived which illustrates the various sources of a nonvanishing phase lag, distinguishes their roles and exposes their unifying feature. Several formally interesting and experimentally relevant limits of the general form are considered and the potential application of phase-sensitive measurements as a route to understanding molecular coupling mechanisms is illustrated.