![]() where 2π phase wrapping occurs.ĭue to fabrication limitations rather than a continuously varying phase delay solid state SPPs have a finite number of discrete phase delay levels 13, 14.Īlternatively, high quality vortex beams with a fixed topological charge may also be generated by sub-wavelength gratings 15, annular gratings 16, meta-materials 17 or by using computer generated holograms 18. The ideal SPP introduces a continuously varying azimuthal phase delay, apart from at the l number of discrete angles where the relative phase delay corresponds to a full wavelength i.e. l, giving rise to a singular point of destructive interference and the formation of a ring-shaped beam in the far-field with a radius proportional to l 12.The central axis of the vortex phase distribution contains all phase values ranging from 0 to 2π Positive and negative values of l describe the handedness of the helices: righthanded vortices are conventionally assigned to positive helical charge. ![]() 1.Īn optical vortex is characterised by its orbital angular momentum or topological helical charge, l, which may take any integer non-zero number, and is equivalent to the number of entwined helices describing the wavefront. Optical vortices may be produced in various manners, but the easiest way to appreciate vortices is to consider the simplest vortex producing device, the spiral phase plate (SPP), which introduces an azimuthally varying retardation in a wavefront as illustrated in Fig. In this work the term will refer to the latter definition. The term optical vortex is used to describe a singular point of zero intensity inside an optical field or a paraxial light beam containing such a singular point. Since then interest into vortices has been growing with the increasing number of applications as diverse as cooling and trapping of droplets 4, neutral atoms and Bose-Einstein condensates 5, 6, manipulation of microscopic particles 7, optical communications 8, solar corona 9, exoplanet observation 10 and stimulated emission depletion microscopy 11. Optical vortices were first mentioned in the pioneering work of Nye and Berry 1 in the 70’s and the first reports on generation of optical vortices were published two decades later 2, 3.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |