  High-harmonic generation from hydrogenlike muonic atoms exposed to
ultraintense high-frequency laser fields is calculated. Systems of low nuclear
charge number Z are considered where a nonrelativistic description applies. By
comparing the radiative response for different isotopes we demonstrate
characteristic signatures of the finite nuclear mass and size in the harmonic
spectra. In particular, for Z>1, an effective muon charge appears in the
Schr\"odinger equation for the relative particle motion, which influences the
position of the harmonic cutoff. Cutoff energies in the MeV domain can be
achieved, offering prospects for the generation of ultrashort coherent
gamma-ray pulses.
