Spiral Phase Distribution Research Articles

Observation and explanation of polarization-controlled focusing of terahertz surface plasmon polaritons

Polarization-controlled focusing of surface plasmon polaritons (SPPs) is experimentally and theoretically investigated in the terahertz (THz) frequency range. The spiral phase distribution and the phase singularities, which, respectively, lead to the transverse shift of the focal spot for the circularly polarized THz radiation and the split of the focal spot for the linearly polarized THz radiation, are experimentally observed. Furthermore, an alternative theoretical model based on the Huygens-Fresnel principle and Fourier transformation of THz SPPs is proposed to analyze the transverse shift of the focal spot, which provides a simple way to understand the polarization-related SPP phenomena. This research is instructive for the design of polarization-based plasmonic devices.

Analysis of the radiation force of a Laguerre Gaussian vortex beam exerted on an uniaxial anisotropic sphere

Based on the expansion of Hermite Gaussian (HG) beam in terms of spherical vector wave functions (SVWFs) utilizing Complex Source Point Method (CSPM) and the relation between HG beam and Laguerre Gaussian (LG) mode, we derived the expansion of LG vortex beam in terms of SVWFs. Using Generalized Lorenz Mie Theory (GLMT), the radiation force (RF) exerted on a uniaxial anisotropic sphere by a LG vortex beam with spiral phase distribution is calculated. The effects of the radial and azimuthal mode index of LG vortex beam, anisotropic permittivity tensor elements, and particle size on the dimensionless axial and transverse RF have been numerically analyzed in detail.

Correlation matching method for high-precision position detection of optical vortex using Shack–Hartmann wavefront sensor

We propose a new method for realizing high-spatial-resolution detection of singularity points in optical vortex beams. The method uses a Shack-Hartmann wavefront sensor (SHWS) to record a Hartmanngram. A map of evaluation values related to phase slope is then calculated from the Hartmanngram. The position of an optical vortex is determined by comparing the map with reference maps that are calculated from numerically created spiral phases having various positions. Optical experiments were carried out to verify the method. We displayed various spiral phase distribution patterns on a phase-only spatial light modulator and measured the resulting singularity point using the proposed method. The results showed good linearity in detecting the position of singularity points. The RMS error of the measured position of the singularity point was approximately 0.056, in units normalized to the lens size of the lenslet array used in the SHWS.

Observation of an x-ray vortex

Phase singularities are a ubiquitous feature of waves of all forms and represent a fundamental aspect of wave topology. An optical vortex phase singularity occurs when there is a spiral phase ramp about a point phase singularity. We report an experimental observation of an optical vortex in a field consisting of 9-keV x-ray photons. The vortex is created with an x-ray optical structure that imparts a spiral phase distribution to the incident wave field and is observed by use of diffraction about a wire to create a division-of-wave-front interferometer.