The near-field and far-field spectral response of
plasmonic systems are often assumed to be identical, due to
the lack of methods that can directly compare and correlate
both responses under similar environmental conditions. We
develop a widely tunable optical technique to probe the near-
field resonances within individual plasmonic nanostructures
that can be directly compared to the corresponding far-field
response. In tightly coupled nanoparticle-on-mirror constructs
with nanometer-sized gaps we find >40 meV blue-shifts of the near-field compared to the dark-field scattering peak, which agrees
with full electromagnetic simulations. Using a transformation optics approach, we show such shifts arise from the different
spectral interference between different gap modes in the near- and far-field. The control and tuning of near-field and far-field
responses demonstrated here is of paramount importance in the design of optical nanostructures for field-enhanced spectroscopy,
as well as to control near-field activity monitored through the far-field of nano-optical devices.