Barriers to spectral resolution imposed by instrumental limits and inhomogeneous broadening can often be removed by linear and nonlinear laser spectroscopy. This is illustrated by the case of LaF3:Pr3+. Six orders of magnitude increase in resolution has been demonstrated, and this uncovered new mechanisms for optical dephasing such as coupling to nuclear spin fluctuations. The importance of the time-scale of the experimental probe is stressed, and the information obtained from spectral holeburning and coherent transients can be very different. This was found in CaF2:Pr3+ where the fluorine nuclear spin-flips exhibit a wide range of time-scales. © 1988.