Electromagnetic analysis of nonparaxial Bessel beams generated by diffractive axicons

The generation of narrow Bessel beams by diffractive axicons for applications such as high-precision alignment requires resonance-domain circular-grating structures. We apply rigorous grating theory locally to determine the amplitudes and phases of all scalar components of the electromagnetic field immediately behind the diffractive element. We then employ the angular spectrum representation to compute far-zone patterns of the diffracted field and the Rayleigh–Sommerfeld formula to determine the field at finite distances in the neighborhood of the optical axis. It is shown that linearly polarized illumination causes considerable circular asymmetry in the diffraction pattern in both cases. This can be avoided by the use of either circularly polarized or unpolarized illumination.