By Nestor Bareza Jr. and Nathaniel Hermosa II
Nestor Bareza Jr. and Nathaniel Hermosa II are both members of the Photonics Research Laboratory. Their article below is a simplified version of their recently published work, which can be accessed here: http://www.sciencedirect.com/science/article/pii/S0030401815006902
Light, as we normally know, propagates in a straight path in the ray optics regime. However, light may possess orbital angular momentum (OAM) in which directional flow of energy is helical as the light propagates. Light with OAM is used as optical spanner or it can induce angular displacement to particles. Light with OAM forms dark regions at which light swirls around. This dark region is called an optical vortex (OV) where the wave amplitude vanishes and the phase is indeterminate. In our recently published paper, we presented the first study of dynamical behaviour of multiple OVs embedded in a helico-conical optical beam (HCOB). HCOB is a special type of light that has inseparable radial and azimuthal phase expressions. Shown in Figure 1 are HCOB intensity profiles with three peripheral OVs and a central OV that are captured experimentally (left image) and obtained numerically (right image). Our technique in observing the OV propagation dynamics utilized calculations of the complex wave amplitude expression and image processing of the acquired intensity profiles. This technique is able to detect the motion of multiple OVs in transverse spatial space at fine-scaled propagation distances. We found that the peripheral OVs have inward motion and when the beam has central OV, significant angular motion is observed (shown in Figure 2). This interaction of OVs influences the wave profile reconstruction of HCOB and its spiralling intensity formation at the far field. This may find application into a more controllable micromanipulation and optical spanner.
As an international research
The study of dynamics of optical vortices (OVs) is essential in understanding its role on wave profile reconstruction of the beam and its influence on the internal energy flow. Its study also paves way for substantial explanations to related physical phenomena such as drift events, gyration and hydrodynamics [1,2]. Our paper presents the first study of multiple OVs in helico-conical optical beam (HCOB). The observations of OV dynamics in HCOB show how it leads to spiraling intensity formation at the far field  and gives better understanding of reconstruction characteristics of self-healing property of HCOB .
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 N. Hermosa, C. Rosales-Guzman, J. Torres, Helico-conical optical beams self-heal, Opt. Lett. 38 (3) (2013) 383-385.