Transformations of the transverse Poynting vector distribution upon diffraction of a circularly polarized paraxial beam.

Usually, the structure of paraxial light beams is characterized by the intensity associated with distribution of the longitudinal energy flow density (Poynting momentum) across the transverse plane. In this work, special attention is paid to the distribution of internal energy flows described by the transverse Poynting momentum (TPM) components. This approach discloses additional polarization-dependent features of the vector beam transformations; in application to the edge diffraction of a circularly polarized (CP) Gaussian beam, it reveals the helicity-dependent asymmetry of the diffracted-field TPM profile characterized by the shifts of the TPM singularity, maximum, etc.

Transverse spin and the hidden vorticity of propagating light fields.

Spatially inhomogeneous fields of electromagnetic guided modes exhibit a complex of extraordinary dynamical properties such as polarization-dependent transverse momentum, helicity-independent transverse spin, spin-associated non-reciprocity and unidirectional propagation, etc. Recently, the remarkable relationship has been established between the spin and propagation features of such fields, expressed through the spin-momentum equations [Proc. Natl.

Mathematical Modelling of Material Transfer to High-Density Lipoprotein (HDL) upon Triglyceride Lipolysis by Lipoprotein Lipase: Relevance to Cardioprotective Role of HDL.

High-density lipoprotein (HDL) contributes to lipolysis of triglyceride-rich lipoprotein (TGRL) by lipoprotein lipase (LPL) via acquirement of surface lipids, including free cholesterol (FC), released upon lipolysis. According to the reverse remnant-cholesterol transport (RRT) hypothesis recently developed by us, acquirement of FC by HDL is reduced at both low and extremely high HDL concentrations, potentially underlying the U-shaped relationship between HDL-cholesterol and cardiovascular disease. Mechanisms underlying impaired FC transfer however remain indeterminate.

Optical-vortex diagnostics via Fraunhofer slit diffraction with controllable wavefront curvature.

Far-field slit diffraction of circular optical-vortex (OV) beams is efficient for measurement of the topological charge (TC) magnitude but does not reveal its sign. We show that this is because in the common diffraction schemes the diffraction plane coincides with the incident OV waist plane. Based on the examples of Laguerre-Gaussian incident beams containing a spherical wavefront component, we demonstrate that the far-field diffracted beam profile possesses an asymmetry depending on the incident wavefront curvature and the TC sign.

Low-temperature laser-stimulated controllable generation of micro-bubbles in a water suspension of absorptive colloid particles.

A method is described for the generation of micrometer-sized vapor-gas bubbles in a water suspension containing absorptive pigment nanoparticles. The diluted suspension (mean interparticle distance 20 μm) absorbs the continuous laser radiation (wavelength 808 nm), and each particle in the best illuminated volume (~10 × 10 × 200 μm) serves as a bubble-nucleation center. The suspension heating is inessential (several degrees above the room temperature) and the bubbles are formed mainly of the air gases dissolved in water.

Electric-current-induced unidirectional propagation of surface plasmon-polaritons.

Nonreciprocity and one-way propagation of optical signals are crucial for modern nanophotonic technology, and typically achieved using magneto-optical effects requiring large magnetic biases. Here we suggest a fundamentally novel approach to achieve unidirectional propagation of surface plasmon-polaritons (SPPs) at metal-dielectric interfaces. We employ a direct electric current in metals, which produces a Doppler frequency shift of SPPs due to the uniform drift of electrons.

Optical Momentum, Spin, and Angular Momentum in Dispersive Media.

We examine the momentum, spin, and orbital angular momentum of structured monochromatic optical fields in dispersive inhomogeneous isotropic media. There are two bifurcations in this general problem: the Abraham-Minkowski dilemma and the kinetic (Poynting-like) versus canonical (spin-orbital) pictures. We show that the kinetic Abraham momentum describes the energy flux and group velocity of the wave in the medium.

Singular skeleton of a Laguerre-Gaussian beam transformed by the double-phase-ramp converter.

We analyze transformations of circular Laguerre-Gaussian beams with zero radial index after passage through the double-phase-ramp (DPR) converter and study the behavior of optical vortices in the propagating transformed beam. Direct and inverse DPR converters are considered, and informative features of the complete set of optical vortices are revealed. For the input beam with even azimuthal index, such a reaction may cause the sign reversal of the axial optical vortex.

Controllable generation and manipulation of micro-bubbles in water with absorptive colloid particles by CW laser radiation.

Micrometer-sized vapor-gas bubbles are formed due to local heating of a water suspension containing absorptive pigment particles of 100 nm diameter. The heating is performed by CW near-infrared (980 nm) laser radiation with controllable power, focused into a 100 μm spot within a 2 mm suspension layer. By changing the laser power, four regimes are realized: (1) bubble generation; (2) stable growth of the existing bubbles; (3) stationary existence of the bubbles and (4) the bubbles' shrinkage and collapse.

Measurement of small light absorption in microparticles by means of optically induced rotation.

The absorption parameters of micro-particles have been associated with the induced spin exerted upon the particle, when embedded in a circularly polarized coherent field. The induced rotational speed is theoretically analyzed, showing the influence of the beam parameters, the parameters of the particle and the tribological parameters of the surrounding fluid. The theoretical findings have been adequately confirmed in experiments.

Transverse energy circulation and the edge diffraction of an optical vortex beam.

Edge diffraction of a circular Laguerre-Gaussian beam represents an example of the optical vortex symmetry breakdown in which the hidden "vortex" energy circulation is partially transformed into the visible "asymmetry" form. The diffracted beam evolution is studied in terms of the irradiance moments and the moment-based parameters. In spite of the limited applicability of the moment-based formalism, we show that the "vortex" and "asymmetry" parts of the orbital angular momentum can still be reasonably defined for the hard-edge diffracted beams and retain their physical role of quantifying the corresponding forms of the transverse energy circulation.

Self-action of continuous laser radiation and Pearcey diffraction in a water suspension with light-absorbing particles.

Water suspension of light-absorbing nano-sized particles is an example of a medium in which non-linear effects are present at moderate light intensities favorable for optical treatment of organic and biological objects. We study experimentally the phenomena emerging in a thin layer of such a medium under the action of inhomogeneous light field formed due to the Pearcey diffraction pattern near a microlens focus. In this high-gradient field, the light energy absorbed by the particles induces inhomogeneous distribution of the medium refraction index, which results in observable self-diffraction of the incident light, here being strongly sensitive to the medium position with respect to the focus.

Extraordinary momentum and spin in evanescent waves.

Momentum and spin represent fundamental dynamic properties of quantum particles and fields. In particular, propagating optical waves (photons) carry momentum and longitudinal spin determined by the wave vector and circular polarization, respectively. Here we show that exactly the opposite can be the case for evanescent optical waves.

Self-diffraction of continuous laser radiation in a disperse medium with absorbing particles.

We study the self-action of light in a water suspension of absorbing subwavelength particles. Due to efficient accumulation of the light energy, this medium shows distinct non-linear properties even at moderate radiation power. In particular, by means of interference of two obliquely incident beams, it is possible to create controllable phase and amplitude gratings whose contrast, spatial and temporal parameters depend on the beams' coherence and power as well as the interference geometry.

Circular motion of particles suspended in a Gaussian beam with circular polarization validates the spin part of the internal energy flow.

Non-spherical dielectric microparticles were suspended in a water-filled cell and exposed to a coherent Gaussian light beam with controlled state of polarization. When the beam polarization is linear, the particles were trapped at certain off-axial position within the beam cross section. After switching to the right (left) circular polarization, the particles performed spinning motion in agreement with the angular momentum imparted by the field, but they were involved in an orbital rotation around the beam axis as well, which in previous works [Y.

Internal energy flows and instantaneous field of a monochromatic paraxial light beam.

It is known that the orbital angular momentum of a paraxial light beam is related to the rotational features of the instantaneous optical-frequency oscillation pattern within the beam cross section [J. Opt. A 11, 094004 (2009)].

Orbital rotation without orbital angular momentum: mechanical action of the spin part of the internal energy flow in light beams.

The internal energy flow in a light beam can be divided into the "orbital" and "spin" parts, associated with the spatial and polarization degrees of freedom of light. In contrast to the orbital one, experimental observation of the spin flow seems problematic because it is converted into an orbital flow upon tight focusing of the beam, usually applied for energy flow detection by means of the mechanical action upon probe particles. We propose a two-beam interference technique that results in an appreciable level of spin flow in moderately focused beams and detection of the orbital motion of probe particles within a field where the transverse energy circulation is associated exclusively with the spin flow.

Rotational transformations and transverse energy flow in paraxial light beams: linear azimuthons.

Paraxial beams whose transverse structure rotates upon free propagation (spiral beams) can be treated as analogs of azimuthons recently found in nonlinear media [Phys. Rev. Lett.

Centrifugal transformation of the transverse structure of freely propagating paraxial light beams.

Superpositions of coaxial Laguerre-Gaussian modes with common waists and the same Gaussian envelopes are known to form beams whose transverse structures experience the self-similar transformation during free beam propagation: the beam shape remains the same except for the divergence and rotation around the propagation axis. We show that under certain conditions this transformation can be represented as if every point of the beam cross section performs a centrifugal straight-line fly off.

Optical vortex symmetry breakdown and decomposition of the orbital angular momentum of light beams.

Two forms of the transverse energy circulation within plane-polarized paraxial light beams are specified: one inherent in wave-front singularities (optical vortices) and the other peculiar to astigmatism and asymmetry of beams with a smooth wave front. As quantitative measures of these energy flow components, the concepts of vortex and asymmetry parts of a beam's orbital angular momentum are introduced and their definitions are proposed on the basis of beam intensity moments. The properties and physical meaning of these concepts are analyzed, and their use for the study of transformations of optical vortices is demonstrated.

Manifestation of the rotational Doppler effect by use of an off-axis optical vortex beam.

We report what is to our knowledge the first all-optical detection of the frequency beats between Gaussian and Laguerre-Gaussian LG0(1) modes in their axial superposition, caused by the rotational Doppler effect. The relation between the observable off-axis optical vortex rotation and the rotational frequency shift of the Laguerre-Gaussian component is ascertained. The results can be used as a physical basis for recognition of Laguerre-Gaussian mode spectra along their orbital angular momenta.