Generation of an optical needle beam with a laser inscribed Pancharatnam-Berry phase element under imperfect conditions

Abstract

Beams exhibiting long focal lines and small focal spot sizes are desired in a variety of applications and are called optical needles, with Bessel beams being a common example. Conical prisms are regularly used to generate Bessel beams, however, this method is usually plagued by an appearance of on-axis oscillations. In this work, we consider an optical element based on the space-domain Pancharatnam-Berry phase (PBP) to generate a high-power optical needle with a smooth and constant on-axis intensity profile. The phase in PBP elements is not introduced through optical path differences but results from the geometric phase that accompanies space-variant polarization manipulation. Our implementation is based on a type 2 modification of bulk transparent glass material, resulting in the formation of nanogratings with slow axes aligned perpendicular to the grating corrugation. We investigate both numerically and experimentally the stability of an optical needle generation under imperfect conditions. Influences of misalignments in the optical schema are investigated numerically and experimentally.

Light Engineering and Silicon Diffractive Optics Assisted Nonparaxial Terahertz Imaging

“…[9,46] An axicon became especially interesting, as it has enabled the generation of the so-called non-diffracting Bessel beam, [46][47][48] which can be further engineered using a flat geometrical phase element. [49] Elliptic Mathieu, [50] parabolic Weber, [51] and self-accelerating Airy beams [52,53] are yet another member of the attractive family of non-diffracting beams. It is worth noting that flat optical elements can handle all those nondiffracting beams efficiently, for instance, to generate Airy beams under various conditions [54] within a wide range of wavelengths extending from optical [53,55] to THz.…”

Creating an Array of Parallel Vortical Optical Needles

“…They have a fixed bell-shaped axial intensity distribution in the Bessel zone [26]. However, this distribution may not be optimal for some applications, such as laser micromachining [17,[27][28][29][30] and optical tweezers [31]. For some applications, such as surface patterning, Bessel beams can provide a less-sensitive process to surface height variations [32][33][34], but shaping the focal region could improve stability even further.…”

“…For some applications, such as surface patterning, Bessel beams can provide a less-sensitive process to surface height variations [32][33][34], but shaping the focal region could improve stability even further. Several methods to create non-diffractive beams with a flat longitudinal intensity distribution have been suggested, for example the implementation of a logarithmic axicon [35,36], modulating the spatial spectrum of the Bessel beam [37,38], or using diffractive optical elements [29,39].…”

Constructing ultra-long focal fields via tightly focused Bessel beams

“…These properties have shown tremendous potential for various practical applications, such as optical lithography [32] , optical data storage [33] , and high-resolution optical imaging [34] . Moreover, different optical elements, such as the Pancharatnam-Berry phase element [35] , the spatial light modulator [36] , periodically poled crystals [37] , and metalenses [38] , are employed to experimentally generate the ultra-long focus field. To increase the length of the optical needle, several methods are proposed, including high NA objective lenses with a diffractive optical element (DOE) [39,40] , a spherical mirror [41] , a Fresnel zone plate [42] , artificial neural networks [43] , and a phase mask [44] .…”