  Intra-Landau level excitations in the fractional quantum Hall regime are not
accessible via optical absorption measurements. We point out that optical
probes are enabled by the periodic potentials produced by a moir\'e pattern.
Our observation is motivated by the recent observations of fractional quantum
Hall incompressible states in moir\'e-patterned graphene on a hexagonal boron
nitride substrate, and is theoretically based on $f-$sum rule considerations
supplemented by a perturbative analysis of the influence of the moir\'e
potential on many-body states.
