Phase dynamics of continuous topological upconversion in vortex beams

Abstract

The vortex emergence process as an integer order Bessel field progresses continuously onto the contiguous higher order Bessel field is studied in detail. We assess the progressive migration of phase singularities and explain the predicted increase in fractional orbital angular momentum content of the beam in terms of this gradual process.

Vortex structure of elegant Laguerre–Gaussian beams of fractional order

“…4 is very similar to the trajectories of the fractional Bessel beams discussed in [8]. An important difference with respect to the Bessel case is that while for fractional Bessel modes the outgoing and incoming transit speeds as λ increases are approximately the same, in the case of the eLG, the axial higher-order vortex is much more unstable when λ decreases than when it is increased respect the integer value.…”

“…We found that under this variation the vortices can be classified in five groups. Contrary to the behavior of the vortices of the nondiffracting Bessel beams of fractional order [7,8], the threedimensional trajectories of the vortex nodal lines in the case of the diffracting eLG beams exhibit much more intricate shapes. We have also observed that the vortex structure of the beams is significantly affected by variations of the angular index rather than variations of the radial index, so we focus our attention in the characterization of this particular variation.…”

“…It is now well-known that the OAM per photon carried by these beams can take an arbitrary value within a continuous range, either integer or noninteger in units of ℏ [3][4][5][6][7][8][9][10][11]. This class of beams can be produced, for example, using either a spiral phase plate whose phase jump is not an integer multiple of 2π [3,4], suitable superpositions of Laguerre-Gaussian beams [5,6], or Bessel beams [7][8][9].…”

“…), providing additional degrees of freedom. In the study of optical beams with noninteger OAM, an accurate mapping of their intricate phase distribution is a critical tool for successfully tracing the dynamics of the fields and observing the mutual interactions of multiple vortices as they propagate [4,8,12].…”

Negative optical spin torque wrench of a non-diffracting non-paraxial fractional Bessel vortex beam

“…Various standard types of laser beams have been suggested and investigated for this purpose [10,11]. Examples of beams also include optical vortices of Gaussian-like [12,13] and nondiffracting beams [14].A particular kind of vortices with fractional topological charge (or order) has received increasing attention due to their special In contrast, another class for factional vortex beams (which can be realized experimentally using blazed-phase hologram encoded in a programmable liquid crystal display illuminated with a He-Ne laser [19]) and displays limited-diffracting features during propagation exists [19,20]. The physically-realizable apodized beam carrying finite energy preserves the nondiffracting propagation property.…”