When I think of a Forster Resonance Energy Transfer (FRET) process, I typically imagine the initial excitation of an absorbing chromophore with a photon followed by the subsequent emission of a lower frequency photon from a secondary emitting chromophore, where this process occurs as a result of dipole-dipole coupling between electronic states of the two chromophores allowing for an InterSystem Crossing (ISC) event.
However, isn't this just because Kasha's rule (http://en.wikipedia.org/wiki/Kasha's_rule) or some variant of this rule, tells us that ISC events are most likely to occur from the lowest excited eigenstate of the initially excited chromophore, where we shed energy non-radiatively to get to this state?
Can't we use a laser and a band-pass filter to directly excite to absorbing chromophore to the lower regime of the first excited singlet state where ISC can occur with high probability (provided the right chromophore system)? Are there examples of "loss-less" FRET energy transfer where the excitation and emission wavelengths are identical or near-identical (e.g. where the wavelengths are less than a nanometer apart)?