  The last 20 years have seen the development of new techniques in
Astroparticle Physics providing access to the highest end of the
electromagnetic spectrum. It has been shown that some sources emit photons up
to energies close to 100 TeV. Yet the fluxes of these photons are incredibly
low and new detection techniques are needed to go higher in energy.
  A new technique that would use the new generation of Cherenkov Telescopes,
i.e., the Cherenkov Telescope Array (CTA), is proposed to push further the
energy frontier. It is based on the detection of the fluorescence radiation
emitted in extensive air showers, a successful method used in ultra-high-energy
cosmic ray experiments, like the Pierre Auger Observatory. It would complement
the standard imaging atmospheric Cherenkov technique with only minor
modifications of the hardware currently being developed for the CTA and would
not imply significant extra costs during its planned operation.
