Diffractive axicons in oblique illumination: analysis and experiments and comparison with elliptical axicons

Abstract

Axicons in oblique illumination produce broadened focal lines, a problem, e.g., in scanning applications. A compact mathematical description of the focal segment is presented, for the first time, to our knowledge, and the results are compared with elliptical axicons in normal illumination. In both cases, analytical expressions in the form of asteroid curves are obtained from asymptotic wave theory and caustic surfaces. The results are confirmed by direct diffraction simulations and by experiments. In addition we show that at a fixed angle an elliptical axicon can be used to compensate for the adverse effects of oblique illumination.

Light beats the spread: “non‐diffracting” beams

“…Careful illumination of such a device is required to avoid any aberrations, notably astigmatism, that can be detrimental to the output mode. Normal incidence illumination of axicon lenses is key to avoid aberrations such as astigmatism, which result in non-circularly symmetric patterns [31][32][33]. If the axicon is illuminated with a converging or diverging beam, one can also change the baseline of the beam profile and obtain an offset or tilt across the beam profile, resulting in a type of biased optical potential energy landscape: such a washboard-like optical potential can be used for optical micromanipulation as we shall see later [34].…”

Optical caustics observed in light scattered by an oblate spheroid

“…An example of such an evolution is the glory caustic for scattering by a spherical bubble in water, which opens to become a four-cusped asteroid caustic for scattering by a spheroidal bubble [43][44][45]. The local transverse cusp caustic described in this section is a portion of the global asteroid caustic for spheroid glory scattering [2].…”

Nonparaxial analysis of continuous self-imaging gratings in oblique illumination

“…However, despite these two qualities, axicons seem to have limitations for wideangle imaging applications. Studies in [10][11][12][13] on the tolerance in angles of axicons have suggested that they are very sensitive to off-axis aberrations, but this needs further investigation. The purpose of this paper is indeed to study the tolerance angle of a particular class of optical components called continuously self-imaging gratings (CSIGs) [14,15].…”