Generating double focal spots by focusing a radially polarized double-ring-shaped beam with an annular classical axicon

Abstract

Focusing properties of a radially polarized double-ring-shaped beam with an annular classical axicon are numerically investigated based on vector Debye theory. Double focal spots and a flat-topped beam can be generated by choosing appropriate values of the pupil to the beam ratio β, numerical aperture, and annular obstruction. The distance between the twin spots, their depth of focus and the depth of the flat-topped beam are considerably affected by numerical aperture and annular obstruction. These focal shapes may find applications in laser printing, multifocal microscopy, and material processing.

Tight focusing of azimuthally polarized Laguerre–Gaussian vortex beams by diffractive axicons

“…Axicons have garnered significant interest in recent years due to their versatility in generating a wide range of beam shapes in the focal region [1][2][3][4]. Linear or classical axicons, which exhibit a linearly increasing on-axis intensity along the optical axis, have proven effective for creating non-diffracting Bessel beams [1,5] and producing diverse focal shapes, including double focal spots [3], flat-topped beams [6], three-dimensional dark spots [7], thin light sheet [8], and very tight focus [9,10]. As a result, linear axicons have found applications in long-range alignment [11], laser machining [12], Bose-Einstein condensates [13], and particle manipulation [14].…”

“…For instance, without phase singularity, polarized multi-ring-shaped beams have been used to generate different focal shapes such as multiple focal segments [31,32], dark channels [33], and sharp focal spots [30]. Furthermore, in our recent study, double focal spots and flat-topped focal segments are generated by focusing a radially polarized double-ring-shaped beam using a linear axicon in the presence of the phase singularity [3]. Therefore, introducing a phase singularity in a tightly focused azimuthally polarized Laguerre-Gaussian vortex beam can produce novel and intriguing focal shapes with distinct properties.…”

“…For example, setting p = 1 yields a doublering-shaped beam, which has been utilized in various applications to generate unique beam shapes in the focal region of axicons or spherical lenses. These applications include multiple optical cages [31], double focal spots [3], and flat-topped beams [36]. By carefully selecting the beam and optical system parameters, these configurations can be achieved.…”

“…The figure clearly demonstrates that the intensity shape undergoes significant changes with varying NA. Generally, reducing the NA value leads to an expansion of the focal region[3]. In the case of the spherical lens and linear axicon, transversely polarized optical needles are formed in the focal region of the APLGV beam, as shown in figure6(a-1:4) and (b-1:4), respectively.…”

Intensity distribution of the partially coherent Gaussian Schell vortex beam diffracted by classical axicon

“…Axicons are versatile optical devices that produce focal lines instead of focal point generated by lenses [1]. Axicons have attracted increasing attention because of their diversity and utility in generating various significant beam shapes within the focal region [1][2][3][4]. The classical axicon, characterized by an on-axis intensity linearly increasing along the optical axis, has been employed for the creation of non-diffracting Bessel beams [5], as well as for producing diverse focal shapes, such as hollow laser beams [6], double focal spots [4], thin-sheet lights [7], tight focal spot sizes [2], flat-topped beams [8], and three-dimensional dark spots [9].…”