Various papers put out by the Goodson group:
And from a separate group at Northwestern:
 Entangled Photon Resonance Energy Transfer in Arbitrary Media
 Suggests three orders of magnitude improvement in crosssection relative to incoherent TPA.
 In SPDC, photon pairs are generated randomly and usually accompanied by undesirable multipair emissions.
 For solidstate artificial atomic systems with radiative cascades (singled quantum emitters like quantum dots), the quantum efficiency is near unity.
 Paper is highly mathematical, and deals with resonance energy transfer (which is still interesting)
Regarding high fluence sources, quantum dots / quantum structures seem promising.
