Abstract :
As an electromagnetic wave propagates through a dispersive material in which the refractive index is a complex function of frequency, those frequencies that lie below the absorption band experience the least amount of attenuation and hence become the dominant contribution to the field for large propagation distances. Asymptotic analysis has shown that in dielectrics, this low-frequency contribution, the so-called Brillouin precursor, has a peak amplitude point that decays algebraically with propagation distance z, as z−1/2 (Oughstun and Sherman, J. Opt. Soc. Amer. B, 5, 817–849, 1988). It has been suggested that near-optimal pulse penetration is possible by using the Brillouin precursor as the transmit pulse, which may then have applicability to radar imaging (Oughstun, IEEE Trans. Ant. Prop., 53, 1582–1590, 2005).
