On Superluminal Propagation and Information Velocity

This paper examines some of the recent experiments on superluminal propagation. It is well known that Sommerfeld and Brillouin analyzed a rectangular sinusoidal signal propagating through a dispersive medium and derived expressions to describe the precursors and the main signal. In this paper, the impulse response of this dispersive medium is derived as exact expression using Taylor series expansion and output signal for any causal input signal is shown to be zero for time $t$ less than vaccum transit time and implications for superluminal information velocity is analyzed.