Abstract
An annular beam with a single uniform-intensity ring and multiple segments of phase gradients is proposed in this paper. Different from the conventional superposed vortices, such as the modulated optical vortices and the collinear superposition of multiple orbital angular momentum modes, the designed annular beam has a doughnut intensity distribution whose radius is independent of the phase distribution of the beam in the imaging plane. The phase distribution along the circumference of the doughnut beam can be segmented with different phase gradients. Similar to a vortex beam, the annular beam can also exert torques and rotate a trapped particle owing to the orbital angular momentum of the beam. As the beam possesses different phase gradients, the rotation velocity of the trapped particle can be varied along the circumference. The simulation and experimental results show that an annular beam with three segments of different phase gradients can rotate particles with controlled velocities. The beam has potential applications in optical trapping and optical information processing.
Highlights
Optical tweezers[1] are powerful tools and extensively used in physics, biology, medical science, and other fields.[2,3,4] A plane wave can be converted into a helical mode with an azimuthal phase of exp(imθ), where m is the topological charge and θ is the azimuthal angle
Different from the conventional superposed vortices, such as the modulated optical vortices and the collinear superposition of multiple orbital angular momentum modes, the designed annular beam has a doughnut intensity distribution whose radius is independent of the phase distribution of the beam in the imaging plane
Based on the iterative beam-shaping algorithm which computes a phase-only hologram to simultaneously shape both the amplitude and phase of an optical beam, we designed an annular beam with different phase gradients in different sections of the annulus
Summary
Multi-ring vortex beam.[23] the width and radius of each of the optical vortex rings are still dependent on the topological charge of the carrying phase. The beam has multiple OAM along the single ring of the intensity distribution and the radius of the ring is independent of the topological charges of the segments. The topological charges of the phase gradients along the annulus can be set arbitrarily for a defined radius of the intensity ring. An experiment on the optical rotation driven by the generated beam will be carried out to verify the segmented phase gradients of the beam
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