Generation of optical phase singularities by computer-generated holograms

Abstract

Laser beams that contain phase singularities can be generated with computer-generated holograms, which in the simplest case have the form of spiral Fresnel zone plates.There has recently been considerable interest in optical fields that exhibit phase singularities, which manifest themselves as isolated dark spots in the modal patterns of certain lasers. Each dark spot has a topological charge that represents the number of 2vr accumulated when the phase gradient is integrated around it. The wave fronts near a singularity have a helical structure, while the field at the singularity must be zero because of the ambiguous phase; hence the dark spot.It has been shown theoretically how, under the influence of nonlinear interactions, frequencydegenerate transverse modes can lock together with a fixed phase difference to produce stable patterns that contain one or more of the singularities.' Such modal patterns have also been observed experimentally. 2 -4 Uncontrolled generation of random arrays of singularities has also been reported. 5 Here we report a means of generating such singularities in a controlled way, using only the simplest equipment, which amounts to the use of a computergenerated hologram, or zone plate. The hologram that is simulated is that of a modal pattern that contains a set of phase singularities using a reference plane wave. The technique can be extended to produce patterns of great complexity, but in this Letter we mainly concentrate on the circularly symmetric doughnut mode. If one interferes two coherent optical fieldsEl exp(iol) and E 2 exp(i0 2 ), the resultant spatial intensity pattern is modulated by a 2ElE 2 cos ((k + 02) term, which represents the interference fringes.The desired interference pattern is between a plane wave and the lowest-order hybrid doughnut mode, 3

Free-Electron Laser Does the Twist

“…The SZP simultaneously imprints a helical phase onto the FEL beam and focuses it, just like an ordinary Fresnel zone plate, generating a focused optical vortex [45]. This possibility was demonstrated with synchrotron radiation [35,46], yet the high photon flux at a FEL imposes serious limitations for the design of such zone plates, as many common materials cannot withstand even the unfocused FEL beam intensity [47].…”

Spectrum of spatial frequency of terahertz vortex Bessel beams formed using phase plates with spiral zones

“…They can 173 Information Technology and Nanotechnology (ITNT-2015) be forked diffraction gratings or a spiral Fresnel plate. The application of amplitude spiral Fresnel plate to formation of beams with a spatial singularity was proposed in [3]. The boundaries of the zones of the plate are described by the following formula:…”

Generation of Optical Vortex Arrays Using Single-Element Reversed-Wavefront Folding Interferometer

“…Optical vortices play significant role for studying OAM of light fields [2,3] and have been widely used in the area of optical tweezers [4], singular optics [5], optical solitons [6], and optical metrology [7,8]. The most commonly used methods for generating OVs with single or multiple charge are synthetic holograms [9], spiral phase plates [10], liquidcrystal cells [11], dielectric wedge [12], and higher-order laser beams [13]. An alternative method for generating OVs efficiently is the use of optical fibers [14] such as, a hollowcore optical fiber for generating doughnut-shaped beam and a holey fiber for generating hollow beam.…”