Bessel-like light beams formed by the two-component scheme consisting of axicon and spherical lens

Abstract

Combination in an optical scheme of rather different elements such as axicons and spherical lenses allows to form light fields with peculiar properties. A simplest example of such a combination contains a single axicon and spherical lens. Though this scheme has been investigated earlier, the region of the so-called secondary focusing (SF-region) localized behind the well-known annular focus has not been studied yet. In this paper we investigate the optical field in this region using analytical and numerical methods. The boundaries of SF-region have been established, and intensity distribution within a given region has been calculated. It has been shown that the near zone of a SF-region is formed as a result of abrupt annular field autofocusing. As to the far zone, the transverse intensity distribution in it is a superposition of an annular field and an oscillating field of axial type. A distance between an axicon and a lens at which the annular field practically disappears has been determined. In this case the intensity distribution in the SF-region has a Bessel profile. The peculiarity of this Bessel beam is that its cone angle depends on the longitudinal coordinate, namely, decreases in inverse proportion to the distance. The characteristic property of such a z-dependent Bessel beam is the absence of its transformation into annular field as it occurs for ordinary Bessel or Bessel–Gaussian beams in the far region. This property is promising for the use of z-dependent Bessel beams for optical communication in free space and remote sensing.