Manipulating neutral particles in Bessel beams: From rings, through fixed helices, to three-dimensional traps

Abstract

The motion of neutral, polarizable atoms (also called neutral particles in this work) in the field of the Bessel beam is considered. It is shown in the numerical way, that the Bessel rings, i.e., the regions of high energy concentration can trap particles of positive polarizability (atoms in reddetuned beams). This trapping occurs only in the plane perpendicular to the wave propagation, and the motion along the beam is unrestricted. When the beam is superposed with the plane wave of the same frequency propagating in the same direction, the particles are guided along helices, fixed in space. The shape of these helices depends on the parameters characterizing the electromagnetic fields but not on the initial state of guided particles. Depending on the vorticity of the Bessel beam, these helices can be made left or right-handed. In the special case of zero vorticity, the helices get degenerated to the true, three-dimensional rings, which can serve as 3D traps. The emerging structure of potential valleys can be applied to parallel guidance or capture several independent atoms, each in its own trap.

Knotted trajectories of neutral and charged particles in Gaussian light beams

“…Up to our knowledge, this interesting issue has not been studied so far. Some simpler trajectories as rings or helices have already been shown to be actually realized, for instance in Bessel beams [16]. It seems worthy of some attention to verify whether the knotted structure can be transferred from the field to particles.…”

“…Theoretical and experimental studies of "structured" light, "non-diffracting" or "accelerating" beams have been developed [1][2][3][4][5][6][7][8] opening a variety of possible applications, in particular for trapping and guiding particles, atoms, molecules or even micrometer-sized objects. Among beams that have gained special interest one can enumerate Laguerre-Gaussian [9][10][11], Bessel [11][12][13][14][15][16], Airy [4,17,18] or Mathieu [19,20] beams.…”

Knotted nodal lines in superpositions of Bessel-Gaussian light beams

“…Such waves, apart from spin, are also endowed with orbital angular momentum. Particular interest of researchers was attracted here by Laguerre-Gaussian [1][2][3] or Bessel [3][4][5][6][7][8] beams possessing a property of vorticity and an associated "charge" or topological index.…”

“…They are connected with the presence of phase singularities, as stated above, since the phase is undetermined for vanishing field. Such areas of suppressed intensity can serve as traps for both polarizable neutral particles with negative polarization constant (such as blue-detuned atoms) [34][35][36][37][38], for charged particles like electrons through the ponderomotive potential [7], and even for micrometer-sized objects. In case of neutral atoms the gradient forces arising from the inhomogeneities of the electric field occur due to the Stark effect [39] and for larger objects the trapping appears via Mie scattering [40][41][42][43].…”

Interaction between vortex beams and diatomic molecules with rotation

“…For a vortex beam of Laguerre-Gaussian mode, which has an azimuthal phase factor e ilφ , it is shown that each photon can averagely carry orbital angular momentum (OAM) of l as well as spin angular momentum (SAM) of ± [1], where l is an integer and refers to the topological charge of the field. To fully understand the mechanical and quantum effects of the angular momentum carried by the vortex beams, over the past few decades, a lot of studies have been proposed about the interactions between vortex beams and various kinds of materials or objects, such as exchanging OAM in quantum-dots [2], particle trapping and manipulation [3][4][5][6][7], interaction with atoms [8][9][10][11].…”