On the derivation of a Golden Rule formula for photoemission in the quadratic response formalism

The photoelectron current at large distances from a probe irradiated by an external light source is investigated for an interacting many-body system. Within the quadratic response formalism the authors derive a Golden Rule formula for the photoelectron current discriminated with respect to the momentum of the detected, asymptotically free electron. This result establishes the general equivalence between the Golden Rule formulation of photoemission and corresponding results derived within the quadratic response formalism in the 'asymptotic limit'.