  The coherent strong coupling of molecules with confined light fields to
create polaritons - part matter, part light - is opening exciting opportunities
ranging from extended exciton transport and inter-molecular energy transfer to
modified chemistry and material properties. In many of the envisaged
applications open access to the molecules involved is vital, as is independent
control over polariton dispersion, and spatial uniformity. Existing cavity
designs are not able to offer all of these advantages simultaneously. Here we
demonstrate an alternative yet simple cavity design that exhibits all of the
the desired features. We hope the approach we offer here will provide a new
technology platform to both study and exploit molecular strong coupling.
Although our experimental demonstration is based on excitonic strong coupling,
we also indicate how the approach might also be achieved for vibrational strong
coupling.
