We have applied the technique of nuclear spin decoupling to the optical regime. In these experiments we selectively eliminated the role of 19F spin fluctuations as the dominant source of dephasing in the 5925A (1D2 / 3H4)Pr3+ optical transition in 0.05% Pr3+: LaF3 at 2K. The homogeneous optical linewidth (FWHM), measured by photon echoes, was reduced from 56 kHz to 6 kHz by on-resonance nutation of 19F in an external magnetic field of 375G. Further reduction of the linewidth to 4.1 kHz was observed by off-resonance irradiation of the fluorines such that their effective field in the rotating frame was at the 'magic angle' (cos -1 1 3) with respect to the external field. © 1980.