  [Background] Photon strength functions are an important ingredient in
calculations relevant for the nucleosynthesis of heavy elements. The relation
to the photoabsorption cross section allows to experimentally constrain photon
strength functions by investigating the photo-response of atomic nuclei.
[Purpose] We determine the photoresponse of $^{66}$Zn in the energy region of
5.6 MeV to 9.9 MeV and analyze the contribution of the "elastic" decay channel
back to the ground state. In addition, for the elastic channel electric and
magnetic dipole transitions were separated. [Methods] Nuclear resonance
fluorescence experiments were performed using a linearly-polarized
quasi-monoenergetic photon beam at the High Intensity $\gamma$-ray Source.
Photon beam energies from 5.6 to 9.9 MeV with an energy spread of about 3% were
selected in steps of 200-300 keV. Two High Purity Germanium detectors were used
for the subsequent $\gamma$-ray spectroscopy. [Results] Full photoabsorption
cross sections are extracted from the data making use of the monoenergetic
character of the photon beam. For the ground-state decay channel, the average
contribution of electric and magnetic dipole strengths is disentangled. The
average branching ratio back to the ground state is determined as well.
[Conclusions] The new results indicate lower cross sections when compared to
the values extracted from a former experiment using bremsstrahlung on
$^{66}$Zn. In the latter, the average branching ratio to the ground state is
estimated from statistical-model calculations in order to analyze the data.
Corresponding estimates from statistical-model calculations underestimate this
branching ratio compared to the values extracted from the present analysis,
which would partly explain the high cross sections determined from the
bremsstrahlung data.
