Abstract
Helico-conical optical beams, different from higher-order Bessel beams, are generated with a parallel-aligned nematic liquid crystal spatial light modulator (SLM) by multiplying helical and conical phase functions leading to a nonseparable radial and azimuthal phase dependence. The intensity distributions of the focused beams are explored in two- and threedimensions. In contrast to the ring shape formed by a focused optical vortex, a helico-conical beam produces a spiral intensity distribution at the focal plane. Simple scaling relationships are found between observed spiral geometry and initial phase distributions. Observations near the focal plane further reveal a cork-screw intensity distribution around the propagation axis. These light distributions, and variations upon them, may find use for optical trapping and manipulation of mesoscopic particles.
Highlights
The field of singular optics, in reference to light beams with phase singularities, has long been a fertile ground for both theoretical and applied research [1,2,3]
In contrast to the ring shape formed by a focused optical vortex, a helico-conical beam produces a spiral intensity distribution at the focal plane
We examine the two-dimensional intensity distribution at the focal plane of a Fourier transforming lens illuminated by a plane wave encoded with a phase described by Eq (3)
Summary
The field of singular optics, in reference to light beams with phase singularities, has long been a fertile ground for both theoretical and applied research [1,2,3]. Other techniques have been demonstrated to generate ring-shaped optical traps [5,6], optical vortices carry an additional phenomenon of imparting an orbital angular momentum to the trapped particles [7,8]. Aside from ψ , the optical beam may have some radial phase dependence. Intensity distributions at defocused planes are explored to create a three-dimensional picture of the light distribution near the focus These distributions are seen to be novel in comparison to those generated by previously considered radial and azimuthal phase functions
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