  Laser spectroscopic studies on minute samples of exotic radioactive nuclei
require very efficient experimental techniques. In addition, high resolving
powers are required to allow extraction of nu- clear structure information.
Here we demonstrate that by using weak atomic transitions, resonance laser
ionization spectroscopy is achieved with the required high efficiency (1-10%)
and precision (linewidths of tens of MHz). We illustrate experimentally and
through the use of simulations how the narrow experimental linewidths are
achieved and how distorted resonance ionization spec- troscopy lineshapes can
be avoided. The role of the delay of the ionization laser pulse with respect to
the excitation laser pulse is crucial: the use of a delayed ionization step
permits the best resolving powers and lineshapes. A high efficiency is
maintained if the intermediate level has a lifetime that is at least of the
order of the excitation laser pulse width. A model that describes this process
re- produces well the observed features and will help to optimize the
conditions for future experiments.
