ABSTRACT
We introduce a new optical vortex coronagraph (OVC) method to determine the angular distance between two sources when the separation is sub-Rayleigh. We have found a direct relationship between the position of the minima and the source angular separation. A priori knowledge about the location of the two sources is not required. The superresolution capabilities of an OVC, equipped with an â = 2 N-step spiral phase plate in its optical path, were investigated numerically. The results of these investigations show that a fraction of the light, increasing with N, from the secondary source can be detected with a sub-Rayleigh resolution of at least 0.1 λ/D.
Subject(s)
Image Interpretation, Computer-Assisted/methods , Models, Theoretical , Telescopes , Computer Simulation , Light , Scattering, RadiationABSTRACT
The circular polarization components of a vortex beam in a uniaxial crystal exhibit complex propagation characteristics. We demonstrate how the amount of splitting may be distinguished by use of a vortex beam. We predict and experimentally verify a threshold angle subtending the crystal and beam axes, below which the splitting is indistinguishable.
ABSTRACT
Experimental and numerical techniques allowed us to predict and verify the existence of a robust phase singularity in the spatial coherence function when a vortex is present. Though observed in the optical domain, this phenomenon may occur in any partially coherent vortex wave.
ABSTRACT
I propose to use as a window the dark core of an optical vortex to examine a weak background signal hidden in the glare of a bright coherent source. Applications such as the detection of an astronomical object, forward-scattered radiation, and incoherent light are described whereby signal enhancements of at least 7 orders of magnitude may be achieved.
ABSTRACT
Optical microsurgical techniques were employed to investigate the mechanical properties of Hechtian strands in tobacco (Nicotiana tabacum) and Ginkgo biloba callus cells. Using optical tweezers, a 1. 5-microm diameter microsphere coated with concanavalin A was inserted though an ablated hole in the cell wall of a plasmolyzed cell and attached to a Hechtian strand. By displacing the adhered microsphere from equilibrium using the optical trapping force, the tensions of individual strands were determined. Measurements were made using both normal and cold-hardened cells, and in both cases, tensions were on the order of 10(-12) N. Significant differences were found in the binding strengths of cold-hardened and normal cultured cells. An increased number density of strands in cold-hardened G. biloba compared with normal cultured cells was also observed. Although no Hechtian strands were detected in any Arabidopsis callus cells, strands were present in leaf epidermal cells. Finally, the movement of attached microspheres was monitored along the outside of a strand while cycling the osmotic pressure.
Subject(s)
Cold Temperature , Ginkgo biloba/ultrastructure , Nicotiana/ultrastructure , Plants, Medicinal , Plants, Toxic , Optics and PhotonicsABSTRACT
An optical vortex soliton induces a graded-index waveguide over an extended propagation distance in a self-defocusing nonlinear optical medium. Using numerical techniques, we determine the waveguide dispersion and optimal size of the guided beam.
ABSTRACT
The propagation dynamics of an optical vortex pair is experimentally confirmed to experience enhanced rotation in a self-defocusing medium. We measured this effect to be 3.5 times larger than in linear media. The enhancement is attributed to nonlinear refraction within the dark vortex cores, permitting the vortices to propagate as vortex filaments.
ABSTRACT
We observed an optical cusp diffraction catastrophe with an initially smooth but elongated Gaussian beam with an aspect ratio of 2:1. Nonlinear and linear diffraction regimes account for the near-field elliptical annulus and the far-field spatially complex astroid.
ABSTRACT
We demonstrate three-dimensional trapping of low-index particles (20-microm-diameter hollow glass spheres in water) by using a single, strongly focused, stationary dark optical vortex laser beam. The holographically generated vortex, which is similar to a TEM(01)* mode beam, was also used to trap and form ring patterns of high-index particles.
ABSTRACT
Signals encoded as highly stable spatial (or temporal) dark solitons can be used in nonlinear-optical devices such as logic gates, interconnects, multiplexers, and filters. The formation of these waves with the use of simple diffracting (dispersing) elements in prototypical devices is analyzed by using the direct-scattering method, which is also outlined. Noncollisional dark-soliton XOR and AND gates and dark-soliton level splitting and bands are also described.
ABSTRACT
We describe the direct experimental measurement of the transverse propagation velocities of dark spatial solitons. Good agreement is obtained from a comparison of the velocities measured experimentally and the velocities predicted by the two-dimensional theory of Zakharov and Shabat [Sov. Phys. JETP 37, 823 (1973)].
ABSTRACT
The nonlinear refractive-index (n(2)) spectrum of ZnSe near the band gap (lambda(gap) approximately 450 nm) at 77 K was measured for the first time to our knowledge by using self-bending of a pulsed laser beam. The maximum nonlinearity, n(2) approximately 1.9 x 10(-8) cm(2)/W, measured by us is anomalously large, which cannot be explained by conventional thermally induced band-gap shrinkage.
ABSTRACT
Continuous-wave self-deflection of an asymmetrical laser beam, with a deflection angle up to eight diffraction widths, and strong attenuation of the on-axis radiation were achieved in a short sodium-vapor cell. We determined that the nonlinear refractive index Deltan varied almost linearly with intensity I, Deltan approximately n(2)I, with n(2) ~ -10(-7) cm(2)/W at ~200 degrees C and intensities less than 220 W/cm(2).
