  We present a theory of the emission of fermion pairs from a superfluid Fermi
gas induced by a photon absorption. In the solid state physics, this type of
process is called double photo-emission (DPE). The spectrum of the induced
two-particle current (or DPE current) provides a direct insight into the
pair-correlation of condensate fermion pairs. We develop a general formalism
for two-particle current induced by DPE by treating the coupling of two Fermi
gases with the time-dependent perturbation theory. This formalism is used to
calculate energy distributions of DPE current from the superfluid Fermi gas in
the BCS-BEC crossover at T=0. We show that the DPE current has distinct
contributions of the condensed pair components and uncorrelated pair states. We
also calculate the angular dependence of DPE current in the BCS-BEC crossover.
The DPE current of the tightly-bound molecules in the BEC regime is found to be
quite deferent from that of the weakly-bound Cooper pairs.
