Multiple bragg regimes exhibited by a chiral sculptured thin film half-space on axial excitation

Axially excited chiral sculptured thin films (STFs) are shown to display the circular Bragg phenomenon in more than one wavelength-regime, owing to the dispersion inherent in their dielectric susceptibilities. With the assumption of the one-resonance Lorentz model for the constitutive parameters in a frequency-domain investigation, two Bragg regimes emerge: One pre-resonant, and the other post-resonant. A wavelength-regime of perfect reflection also appears. The pulse-bleeding mechanism previously shown to underlie the pre-resonant Bragg regime turns out to be responsible also for the post-resonant Bragg regime. Femtosecond pulse propagation in the post-resonant regime would be very likely affected by the existence of multiple Bragg and perfectly reflecting regimes.