Truncation effect on precursor field structure of pulse propagation in dispersive media

The dynamic evolutions of full Gaussian and particularly the truncated Gaussian pulses in dispersive Lorentz media are studied numerically in detail. The observed qualitative phenomena lead to revised interpretation regarding both Sommerfeld and Brillouin precursors. Neither strict Sommerfeld nor Brillouin precursor is present for the case of an incident full Gaussian pulse for any finite propagation distance. In addition, the Brillouin effect can be separated into a tail and a forerunner depending on the turn-on point of the initial pulse. Moreover, the essence of an artificial precursor is discussed, which deserves caution when handling the high dynamic range problems by numerical algorithm.