Simple expressions for Bragg reflection from axially excited chiral sculptured thin films

Reported here is the derivation of analytic expressions for the reflection coefficients of a halfspace filled by a chiral sculptured thin film (STF) that is axially excited by a normally incident plane wave at the centre-wavelength of the Bragg regime. Although these expressions are correct to the second order with respect to a small parameter that delineates the local anisotropy of the chiral STF, their first-order reductions are particularly simple and very adequate for practical purposes. A small difference between the two cross-polarized reflection coefficients has also been found. The results are explained on the basis of a simple model which utilizes the standard Fresnel equations for a scalar dielectric halfspace, combined with coupled wave theory.