Radio frequency plasmas are widely employed in the microelectronics industry because they provide a means for anisotropic fabrication of microscopic patterns under low temperature conditions. Many of the engineering aspects of plasma processing can be understood in terms of a modified chemical vapor transport theory. In this theory, the transport of reactants and products is driven by gradients in concentration and temperature. Ion transport is driven by gradients in electric potential or sheath fields. The acceleration of ions along the field lines leads to enhanced neutral chemistry along the surface normal (the so-called ion-neutral synergism). While the transport theories as they exist now are useful frameworks from which to design or optimize processes, they address neither the microscopic origin of synergistic effects nor the effects of time-varying gradients, which may be particularly important in rf plasmas. The subject of this paper is the use of time-resolved optical diagnostics to measure time-varying plasma phenomena. In particular, we discuss how laser-induced fluorescence (LIF) spectroscopy can be used to measure plasma formation and decay rates, concentration gradients, and electric fields. The effects of the time-varying applied potential are monitored by firing the laser synchronously with the field. These time-resolved measurements lead to a better understanding of previous, time-averaged, measurements of ion densities and sheath thicknesses as a function of frequency and provide definite limits for the applicability of steady state plasma transport theories.