We propose and experimentally implement a method for the generation of a wide class of partially spatially coherent vortex beams whose cross-spectral density has a separable functional form in polar coordinates. We study phase singularities of the spectral degree of coherence of the new beams.

No abstract

It is shown that, for an incoherent superposition of the orthogonally polarized laser beams, the vector singularities of a specific type arise at the transversal cross section of a paraxial combined beam instead of common singularities, such as amplitude zeros or optical vortices (inherent in scalar, i.e. homogeneously polarized, fields), and C points, where polarization is circular, and L lines, along which polarization is linear (inherent in completely coherent vector, i.e. inhomogeneously polarized fields). There are U lines (closed or closing at infinity) along which the degree of polarization equals zero and the state of polarization is undetermined, and isolated P points where the degree of polarization equals unity and the state of polarization is determined by the non-vanishing component of the combined beam. U surfaces and P lines correspond to such singularities in three dimensions, by analogy with L surfaces and C lines in three-dimensional completely coherent vector fields. P lines directly reflect the snake-like distortions of a wavefront of the singular component of the combined beam. Crossing of the U line (surface) is accompanied by a step-like change of the state of polarization onto the orthogonal one. U and P singularities are adequately described in terms of the complex degree of polarization with the representation at the Stokes space, namely at and inside of the Poincaré sphere. The conditions of topological stability of U and P singularities are discussed, as well as the peculiarities of the spatial distribution of the degree of polarization in the closest vicinity to such singularities. Experimental examples of reconstruction of the combined beam's vector skeleton formed by U and P singularities as the extrema of the complex degree of polarization are given. Comparison with the related investigations is provided.

Mechanical action caused by the optical forces connected with the canonical momentum density associated with the local wavevector or Belinfante's spin angular momentum is experimentally verified. The helicity-dependent and the helicity-independent forces determined by spin momenta of different nature open attractive prospects for the use of optical structures for manipulating minute quantities of matter of importance in nanophysics, nanooptics and nanotechnologies, precision chemistry and pharmacology and in numerous other areas. Investigations in this area reveal new, extraordinary manifestations of optical forces, including the helicity-independent force caused by the transverse helicity-independent spin or vertical spin of a diagonally polarized wave, which was not observed and exploited up to recently. The main finding of our study consists in a direct experimental demonstration of the physical existence and mechanical action of this recently discovered extraordinary transverse component of the spin here arising in an evanescent light wave due to the total internal reflection of a linearly polarized probing beam with azimuthal angle 45° at the interface between the birefringent plate and air, which is oriented perpendicularly to the wavevector of an evanescent wave and localized over the boundary of the transparent media with polarization-dependent refraction indices. Dennis, A. Y. Bekshaev, K. Y. Bliokh, and F. Nori, "Direct measurements of the extraordinary optical momentum and transverse spin-dependent force using a nano-cantilever," Nat. Phys. 12(8), 731-735 (2016). 12. A. Aiello, P. Banzer, M. Neugebauer, and G. Leuchs, "From transverse angular momentum to photonic wheels," Nat.

When the surface roughness is comparable with the wavelength of the probing radiation, the scattered field contains both the regular (forward-scattered) component of coherent nature and the diffusely scattered part. Coloring of the regular component of white light scattered by a colorless dielectric slab with a rough surface is considered as a peculiar effect of singular optics with zero (infinitely extended) interference fringes. To explain the observed alternation of colors with respect to the increasing depth of the surface roughness, we apply a model of transition layers associated with the surface roughness. By applying the chromascopic technique, it is shown that the modifications of the normalized spectrum of the forwardscattered white light can be interpreted as the effect of a quarter-wavelength (anti-reflecting) layer for some spectral component of a polychromatic probing beam.