Small focal spot formation by vector beams

Kozawa, Yuichi; Sato, Shunichi

doi:10.1016/bs.po.2021.01.001

Cited by 14 publications

(5 citation statements)

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“…Laguerre-Gaussian vortex beams with different radial modes (p > 0), known as multi-ring-shaped beams, have garnered growing attention due to their distinctive characteristics, making it a promising model in the field of beam shaping. The destructive interference between the rings in high-order Laguerre-Gaussian beams is effectively reduced the focal spot [30]. 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].…”

Section: Introductionmentioning

confidence: 99%

“…The destructive interference between the rings in high-order Laguerre-Gaussian beams is effectively reduced the focal spot [30]. 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].…”

Section: Introductionmentioning

confidence: 99%

“…In addition, for |m| = 1 the first-order vortex phase singularity, there is a maximum intensity on the optical axis; otherwise, there is zero intensity on the optical axis i.e. hollow profile is formed along the optical axis [30].…”

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

Alkelly,

Al-Ahsab,

Cheng

et al. 2024

Phys. Scr.

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This study presents a comprehensive theoretical investigation into the focusing properties of azimuthally polarized Laguerre-Gaussian vortex (APLGV) beams when interacting with diﬀerent optical elements, including a linear axicon, binary axicon, and lens based on the Debye approximation. The research ﬁndings highlight the intriguing combination of polarization and vortex singularities within the APLGV beam, which result in distinctive focal shapes when interacting with these optical elements. The focal shapes achieved include multiple tightly focused spots and optical needles, which can be controlled by adjusting optical system parameters and beam characteristics such as the numerical aperture (NA), truncation parameter, beam order, and annular obstruction. These parameters can be carefully selected to achieve speciﬁc focal shapes with applications in multi-optical manipulation, particle acceleration, and trapping. By harnessing the unique properties of APLGV beams and optimizing the optical setup, researchers can explore new possibilities for advanced optical manipulation and control.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Alkelly,

Al-Ahsab,

Cheng

et al. 2024

Phys. Scr.

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“…Vector laser beams are laser beams where the polarization is not constant in space, and cylindrical vector beams (CVBs) are a specific case of vector beams where the polarization distribution is cylindrically symmetric [1]. Such CVBs have been well known for some time to create a smaller focal spot than linearly polarized beams when tightly focused [2,3], which can have an important impact on microscopy [4,5], for example. Beyond that, the specific arrangement of the intensity distribution around the focus can result in interesting properties for particle manipulation [6].…”

Section: Introductionmentioning

confidence: 99%

Analytical fields of ultrashort radially polarized laser beams with spatial chirp

Jolly,

Porras

2024

J. Opt. Soc. Am. B

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We find the analytical electromagnetic fields, both paraxial and with non-paraxial corrections, of an ultrashort radially polarized pulse-beam that has spatial chirp. This represents a powerful description of light that has a combination of both vector polarization and space-time structure, and it results in a novel evolution of the fields. The non-paraxial corrections allow for the application of the field solutions to tightly focused scenarios, whereby we can validate our solution via charged particle trajectories under the influence of such a pulse with high field strength.

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“…究者还发现光针可应用于光学相干层析显微成像 [6] 和光声显微成像 [7] ，以实现大焦深的显微成像，因此如何获得横向尺寸更小，纵向长度更长的超分辨光针成为后续急需解决的问题。超分辨光针的产生方法研究目前主要集中于柱矢量偏振光，虽然最新的研究结果表明 [6] ，使用多焦点控制技术可以不依赖光束偏振态获得超长焦深的光针，但其横向分辨率仍然无法与柱矢量偏振光光针相比，且随着光针横向分辨率的提升，光源的衍射效率会急剧下降，当横向分辨率达到衍射极限时，其衍射效率只有不到 2%，所以此方法并不适用于实现超分辨光针。径向偏振光最常被用于实现超分辨光针。2008 年，Wang 等设计了 5 环带的环形二元相位板，对径向偏振贝塞尔高斯光束进行了波前相位调制，将大部分能量调制到了纵向分量上，实现了横向半高全宽(full-width at half-maximum， FWHM)为 0.43 ，纵向 FWHM 为 4 的聚焦电场，并提出了光针的概念 [8] ，极大推动了该方向的研究进展。2010 年，Li 等提出了环形二元相位板的优化设计方法 [9] 。2013 年，Guo 等设计了 17 环带的复杂二元相位板，使用高阶径向偏振拉盖尔高斯光束实现了横向 FWHM 为 0.41 ，纵向 FWHM 为 9.53 的光针 [10] 。随后，这一指标再未得到明显提升，直到 2020 年，Zhang 等人更改了波前调制思路，使用多焦点再融合的思想，用扇形相位板对径向偏振贝塞尔高斯光束进行了调制，实现了横向 FWHM 为 0.6 ，纵向 FWHM 为 20.3 的超长光针 [11] 。这种调制方法虽然大幅增加了光针的纵向长度，但缺点是横向分辨率也大幅下降了，甚至未能突破衍射极限。2021 年，Huang 等改进了环形二元相位板的优化设计方法 [12] ，分别使用 14 环带和 27 环带实现了纵向 FWHM 为 24 和 43 的超长光针，但由于环带数量较多，较难实验实现。随着涡旋光束研究的飞速发展，研究者发现拓扑荷数为 1  的角向偏振涡旋光束紧聚焦后也可获得超分辨焦斑，且焦斑尺寸甚至小于径向偏振光的结果 [13] ，因此有研究者开始尝试利用此种光束来实现超分辨光针。2011 年，Yuan 等利用环形二元相位板波前调制的方法，使得 1 阶角向矢量涡旋光束紧聚焦后获得了长度约为 5 的光针 [14] 。2014 年，Gu 等使用类似的方法，将光针长度提升到约 7 [15] 。2021 年，Shi 等利用宽度为 80.7 m  窄带环形光阑对 1 阶角向涡旋矢量光束进行了遮挡，实验实现了横向 FWHM 为 0.416 ，纵向 FWHM 为15.6 的超长光针 [16] 。这一结果在保持超分辨的前提下，大幅提升了光针长度，但由于使用了超窄带光阑遮挡，因此光源的衍射效率极低。2022 年，Pan 等同时调制了光束的振幅和相位，结果表明使用多环形 1 阶角向涡旋矢量光束结合相位调制可实现长度约为10 的光针 [17] 。如前所述，超分辨光针的研究主要集中于径向偏振光和 1 阶角向矢量涡旋光。其中前者的研究已较为成熟 [18,19] ，径向偏振光紧聚焦可视为位于焦点位置的纵…”

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The study of tight focusing characteristics of azimuthally polarized vortex beams and the implementation of ultra-long super-resolved optical needle

chi¹,

Geng²

2023

Acta Phys. Sin.

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In this paper, the tight focusing characteristics of azimuthally polarized vortex beams are systematically investigated. The azimuthally polarized vortex beam can be decomposed into left-handed and right-handed circularly polarized (LHCP and RHCP) waves. It is found that the longitudinal components of LHCP and RHCP at the focal plane are equal in magnitude and opposite in phase. Thus, the total longitudinal field disappears because of the complete destructive interference. In contrast, there is almost no interference between the transverse components of LHCP and RHCP. Thus, the total transverse field is the incoherent superposition of them. Since the absolute values of the topological charges of LHCP and RHCP components are not equal, the transverse components of LHCP and RHCP will concentrate on the different areas at the focal plane. It is the reason for the orbit-induced localized SAM at the focal plane. Then, we compare the focal spot characteristics of the radially polarized beam and the azimuthally polarized beam with a first-order vortex. The advantages and disadvantages of them are discussed in detail, respectively. For the radially polarized beam, the central focal spot is mainly longitudinal component, and the sidelobe is mainly transverse component. For the azimuthally polarized vortex beam with l=1, the central focal spot is mainly LHCP component, and the sidelobe is mainly RHCP component. In both cases, the field distribution of the central spot is the same, and both show a distribution similar to the zero-order Bessel function. The situation of the sidelobe is different. The sidelobe of the radially polarized beam shows a distribution similar to the first-order Bessel function and the sidelobe of the azimuthally polarized vortex beam shows a distribution similar to the second-order Bessel function. Therefore, the sidelobe of the radially polarized beam is closer to the optical axis, resulting in a larger central focal spot size. On the other hand, the sidelobe of the radially polarized beam accounts for a much smaller proportion of the total energy compared with that of the azimuthally polarized vortex beam. So the sidelobe peak intensity of the radially polarized beam is lower. Finally, an optimal binary phase element is designed to obtain an ultra-long super-resolution optical needle. The transverse FWHM can achieve 0.391λ and the longitudinal FWHM can achieve 25.5λ using only 6 belts.

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Small focal spot formation by vector beams

Cited by 14 publications

References 152 publications

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

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

Analytical fields of ultrashort radially polarized laser beams with spatial chirp

The study of tight focusing characteristics of azimuthally polarized vortex beams and the implementation of ultra-long super-resolved optical needle

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