A laser deflection measurement system has been developed which is both fast (&tgr;≊20 ns) and sensitive (&dgr;&fgr;≊0.5 &mgr;rad). This diagnostic is capable of sensing and discriminating between electrons and neutral particles in a multicomponent plasma, and yields quantitative results. The technique allows continuous measurements in time. Construction is inexpensive and simple to field. This system is, therefore, highly competitive with traditional techniques in diagnosing the development of transient plasmas.