Abstract
Generally, polarization and phase are considered as two relatively independent parameters of light, and show little interaction when a light propagates in a homogeneous and isotropic medium. Here, we reveal that orbital angular momentum (OAM) of an optical vortex beam can be modulated by specially-tailored locally linear polarization states of light under a tightly-focusing conditon. We perform both theoretical and experimental studies of this interaction between vortex phase and vector polarization, and find that an arbitrary topological charge value of OAM can be achieved in principle through vector polarization modulation, in contrast to the spin-orbital conversion that yields only the ± ћ OAM values through circular polarization. We verify the modulation of optical OAM state with vector beams by observing the orbital rotation of trapped particles.
Highlights
Process arises under a high NA focusing configuration cooperated with an incident light with specially tailored locally linear state of polarization
By tightly-focusing a vector-vortex beam, the orbital angular momentum (OAM) states of incident light can partly split into two OAM modes along the radial direction determined by the polarization states, giving rise to two categories of helical wavefront for the longitudinal electric field component
The carefully tailored locally linear state of polarization works like a special modulator that controls the two desired modes of the split OAM states and achieves manipulation of the optical OAM with arbitrary topological charges
Summary
Derivation for the focal field of tightly focused locally linearly polarized vortex beams. In which g0 represents the radial component in the kis a unit vector along the propagation direction, object space, g0 × kdenotes the azimuthal component where and the unit vector e0 describes the polarization distributions of the incident field (Equation (1)). Let θ and φ represent the polar and azimuthal angles of the focused ray, the radial unit vector before and after refraction, can be expressed as: g0 = −cos φ i − sin φj (11). The Cartesian components of the electric field vector near focus can be expressed as Eqs (3–5). The desired vector-vortex beams can be achieved making use of an azimuthal analyzer for filtering out the radial components. The generated vector-vortex beams are subsequently tightly-focused by an oil-immersion objective lens [Olympus 100×, NA = 1.45] onto a glass substrate for trapping particles
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