  In this paper we consider the possibility and conditions for pair
photoemission whereby two incident photons emit pairs of electrons from a
candidate material as a novel method to measure and visualize electronic
correlations. As opposed to double photoemission - where a single photon
precipitates the ejection of a pair electrons via a subsequent electron energy
loss scattering process - we show that pair photoemission need not be limited
to interference between initial photoelectrons and valence electrons, and
moreover, can occur without the energy penalty of two work functions. This
enables detection of pairs of electrons at high energy resolution that may be
correlated in the same quantum many-body states.
