High density, low pressure plasma sources utilizing modulated power have been attracting much attention recently. By modulating the power it is possible to further optimize and control the performance of processing plasmas by changing the pulse frequency and the duty ratio. Pulsing is also of interest for studies of basic plasma physics and pulsed argon discharges are useful benchmarks for a better understanding of the more complex mechanisms involved in pulsed plasma processing with electronegative discharges. Experimental and analytical analyses of helicon discharges in continuous and pulsed excitation using various gases (argon, oxygen) are used to present the main features of pulsed plasma processing. Three phases can be distinguished in a pulsed discharge, the breakdown phase, the steady-state phase and the post-discharge, which affect the processing in various ways as a result of temporal changes in the ion energy distribution function, plasma potential, plasma density and electron temperature. Details on the pulsed deposition of silicon dioxide using silane/oxygen mixtures are given to illustrate the effect of those temporal changes on the quality of the deposited films.