Generation and Propagation of Partially Coherent Power-Exponent-Phase Vortex Beam

We report on a partially coherent power-exponent-phase vortex beam (PC-PEPV), whose spatial coherence is controllable and the initial phase exhibits a periodic power exponential change. The PC-PEPV beam was generated experimentally with various spatial coherence widths, and its propagation properties were studied both numerically and experimentally. By modulating the topological charge (TC) and power order of the PC-PEPV beam, the structure of the vortex beam can be adjusted from circular to elliptic, triangular, quadrangle, and pentagon. When the power order is odd, the PC-PEPV beam with a negative TC can be generated, and the profiles of the PC-PEPV beam can be precisely controlled via adjusting the value of the power order. For the case of high spatial coherence width, the number of the dark cores in the polygonal intensity array of the PC-PEPV beam equals the magnitude of the TC. However, when decreasing the spatial coherence width, the dark cores vanish and the intensity gradually transforms into a polygonal light spot. Fortunately, from the modulus and phase distributions of the cross-spectral density (CSD), both the magnitude and sign of the TC can be determined. In the experiment, the modulus and phase distribution of the CSD are verified by the phase perturbation method. This study has potential applications in beam shaping, micro-particle trapping, and optical tweezers.

Average Intensity and Beam Quality of Hermite-Gaussian Correlated Schell-Model Beams Propagating in Turbulent Biological Tissue

The propagation characteristics of a Hermite-Gaussian correlated Schell-model (HGCSM) beam in the turbulence of biological tissue are analyzed. The average intensity, spectral degree of coherence, and the dependence of the propagation factors on the beam orders, transverse coherence width, fractal dimension, characteristic length of heterogeneity, and small length-scale factor are numerically investigated. It is shown that the HGCSM beam does not exhibit self-splitting properties on propagation in tissues due to the strong turbulence in the refractive index of biological tissue. The larger the beam orders, the fractal dimension, and the small length-scale factor are, or the smaller the transverse coherence width and the characteristic length of heterogeneity are, the smaller the normalized propagation factor is, and the better the beam quality of HGCSM beams in turbulence of biological tissue is. Moreover, under the same condition, the HGCSM beam is less affected by turbulence than of Gaussian Schell-model (GSM) beam. It is expected that the results obtained in this paper may be useful for the application of partially coherent beams in tissue imaging and biomedical diagnosis.

Generation and Propagation of a Hermite-Gaussian Correlated Schell-Model LG0l Beam

A partially coherent beam under the combined action of a Hermite-Gaussian correlated function and vortex phase, named the HGCSMLG0l beam has been explored both theoretically and experimentally. The statistical properties, such as the intensity and distribution of the degree of coherence (DOC) on propagation are analyzed in detail, based on the deduced equations. We find that the intensity is determined dominantly by the non-conventional correlated function when the coherence length is comparatively small and by vortex phase when the coherence length is large. The modulus of the DOC is not vulnerable to coherence width, rather, it is affected by both non-conventional correlated function and vortex phase. Our results are verified well by the experiment results.

Generation of an Adjustable Optical Cage through Focusing an Apertured Bessel-Gaussian Correlated Schell-Model Beam

An adjustable optical cage generated by focusing a partially coherent beam with nonconventional correlation function named the Bessel–Gaussian correlated Schell-model (BGCSM) beam is investigated in detail. With the help of the generalized Huygens–Fresnel integral and complex Gaussian function expansion, the analytical formula of the BGCSM beam passing through an apertured ABCD optical system was derived. Our numerical results show that the generated optical cage can be moderately adjusted by the aperture radius, the spatial coherence width, and the parameter β of the BGCSM beam. Furthermore, the effect of these parameters on the effective beam size and the spectral degree of coherence were also analyzed. The optical cage with adjustable size can be applied for particle trapping and material thermal processing.