In this paper, we explain how a weak optical quadrupole interaction in atoms can be utilized. Our proposed physical model is based on the atom, which interacts at near resonance with laser light prepared as a Bessel mode. This type of beam is a class of light, which possesses a well-defined orbital angular momentum that is distinct from spin angular momentum. This property, in particular, causes optical forces to ensue from such interactions, giving distinctive features. Although the magnitude of the quadrupole interaction in standard situation is small, it plays an important role in some special cases, such as those allowing processes involving dipole-forbidden transitions or in the presence of external fields. We describe the essential features of the optical-force effects and discuss how they can, in principle, be used to influence atoms.

The influences of quadrupole-active transitions for atoms in bessel light modes

Abstract. Surface plasmons (SPs) are electromagnetic surface waves that propagate at the interface between a conductor and a dielectric. Due to their unique ability to concentrate light on two-dimensional platforms and produce very high local-field intensity, SPs have rapidly fueled a variety of fundamental advances and practical applications. In parallel, the development of metamaterials and metasurfaces has rapidly revolutionized the design concepts of traditional optical devices, fostering the exciting field of meta-optics. This review focuses on recent progress of meta-optics inspired SP devices, which are implemented by the careful design of subwavelength structures and the arrangement of their spatial distributions. Devices of general interest, including coupling devices, on-chip tailoring devices, and decoupling devices, as well as nascent SP applications empowered by sophisticated usage of meta-optics, are introduced and discussed.

Meta-optics inspired surface plasmon devices

Surfaces plasmon polaritons carrying orbital angular momentum (OAM), known as plasmonic vortex, hold potential applications for on-chip information multiplexing. However, a traditional plasmonic vortex lens was usually designed for monochromatic incident light and encountered challenges in generating multiple vortices. Here, we demonstrated a wavelength-tunable plasmonic vortex generator that ameliorates these limits, relying on the simultaneous design of a geometric metasurface on an Archimedean spiral. Through this design strategy, both the topological charges and the location of vortices can be controlled with different wavelengths of incident beams. This design and concept can preserve incident wavelength information and can be further applied to integrated and high-dimensional on-chip devices.

https://www.mdpi.com/2304-6732/9/11/809/pdf?version=1666870073

Generation of Tunable Plasmonic Vortices by Varying Wavelength of Incident Light

In this work, an atomic mirror scheme that operates by both quadrupole interaction and evanescent light field is suggested and evaluated. This type of light mode is normally created via the total internal reflection process of laser light beam at the interface of a dielectric medium with a vacuum region. Under the quantum atomic rules in which quadrupole interaction is permissible, we show the optical quadrupole potential and the resulting reflection process of cesium atoms. The efficiency of the atomic reflection process can be enhanced by coating the dielectric surface with a thin metallic film. This increases the magnitude of the evanescent light field and simultaneously reduces the atom–surface attraction, which is considered one of the most prominent obstacles to the atomic reflection process. The performance of the atomic mirror action and some related factors controlling the enhancement in general are pointed out and discussed in this work.

Construction of an Active Atomic Mirror via Quadrupole Transition

Surfaces plasmon polaritons carrying orbital angular momentum (OAM), known as plasmonic vortex, hold potential applications for on-chip information multiplexing. However, a traditional plasmonic vortex lens was usually designed for monochromatic incident light and encountered challenges in generating multiple vortices. Here, we demonstrated a wavelength-tunable plasmonic vortex generator that ameliorates these limits, relying on the simultaneous design of a geometric metasurface on an Archimedean spiral. Through this design strategy, both the topological charges and the location of vortices can be controlled with different wavelengths of incident beams. This design and concept can preserve incident wavelength information and can be further applied to integrated and high-dimensional on-chip devices. 

The total internal reflection of an optical mode with a phase singularity, such as a Bessel beam, can generate evanescent light that displays a rotational property. Notably, using a metallic layer surface, field components extending into the vacuum region have vortex properties besides surface plasmonic features. This vortex retains the phase singularity of the original light, and also maps its associated orbital angular momentum of incident Bessel light of the order l  > 0. Additionally to a two-dimensional patterning on the metallic surface, the strongly restricted intensity distribution decays with distance vertical to the metallic surface. The detailed characteristics of this vortex structure depend on the input light parameters and the dielectric mismatch of the media. As well as this, they can be controlled by varying the incident angle and the order of Bessel light.

S. Al-Awfi

Papers

Formation of a Plasmonic Surface Optical Vortex by Evanescent Bessel Light