  The impact of coherent light propagation on the excitation and fluorescence
of thorium nuclei in a crystal lattice environment is investigated
theoretically. We find that in the forward direction the fluorescence signal
exhibits characteristic intensity modulations dominated by an orders of
magnitude faster, sped-up initial decay signal. This feature can be exploited
for the optical determination of the isomeric transition energy. In order to
obtain a unmistakable signature of the isomeric nuclear fluorescence, we put
forward a novel scheme for the direct measurement of the transition energy via
electromagnetically modified nuclear forward scattering involving two fields
that couple three nuclear states.
