Vladlen Shvedov

Optical guiding of absorbing nanoclusters in air

We suggest a novel approach in all-optical trapping employing a photophoretic force for manipulation of absorbing particles in open air. We demonstrate experimentally the robust three-dimensional guiding, over the distances of a few millimeters, of agglomerates of carbon nanoparticles with the size spanned from 100 nm to 10 microm, as well as their acceleration up to velocities of 1 cm/sec. We achieve stable positioning and guiding of particles as well as simultaneous trapping of a large number of particles in a dual-beam optical trap created by two counter-propagating and co-rotating optical vortex beams.

Photophoretic manipulation of absorbing aerosol particles with vortex beams: theory versus experiment

We develop a theoretical approach for describing the optical trapping and manipulation of carbon nanoclusters in air with a dual-vortex optical trap, as realized recently in experiment [V. Shvedov et al., Opt. Express 17, 5743 (2009)]. We calculate both longitudinal and transverse photophoretic forces acting on a spherical absorbing particle, and then compare our theoretical predictions with the experimental data.

Materials processing with a tightly focused femtosecond laser vortex pulse

In this Letter we present the first (to our knowledge) demonstration of material modification using tightly focused single femtosecond laser vortex pulses. Double-charge femtosecond vortices were synthesized with a polarization-singularity beam converter based on light propagation in a uniaxial anisotropic medium and then focused using moderate- and high-NA optics (viz., NA=0.45 and 0.9) to ablate fused silica and soda-lime glass. By controlling the pulse energy, we consistently machine micrometer-size ring-shaped structures with <100nm uniform groove thickness.

Spatially engineered polarization states and optical vortices in uniaxial crystals

We describe how the propagation of light through uniaxial crystals can be used as a versatile tool towards the spatial engineering of polarization and phase, thereby providing an all-optical technique for vectorial and scalar singular beam shaping in optics. Besides the prominent role played by the linear birefringence, the influence of circular birefringence (the optical activity) is discussed as well and both the monochromatic and polychromatic singular beam shaping strategies are addressed. Under cylindrically symmetric light-matter interaction, the radially, azimuthally, and spirally polarized eigen-modes for the light field are revealed to be of a fundamental interest to describe the physical mechanisms at work when dealing with scalar and vectorial optical singularities. In addition, we also report on nontrivial effects arising from cylindrical symmetry breaking, e.g. tilting the incident beam with respect to the crystal optical axis.

Selective trapping of multiple particles by volume speckle field

We suggest a new approach for selective trapping of light absorbing particles in gases by multiple optical bottle-beam-like traps created by volume speckle field. We demonstrate stable simultaneous confinement of a few thousand micro-particles in air with a single lowpower laser beam. The size distribution of trapped particles exhibits a narrow peak near the average size of an optical speckle. Thus, the speckleformed traps act as a sieve with the holes selecting particles of a similar size.

Dynamics of optical spin-orbit coupling in uniaxial crystals

We study theoretically and verify experimentally the detailed dynamics of spin-to-orbital angular momentum conversion for a circularly polarized Gaussian beam propagating along the optical axis of a uniaxial crystal. We extend the results to the case of white-light beams when each of the spectral components undergoes its own wavelength-dependent angular momentum conversion process.

Generation of higher-order optical vortices by a dielectric wedge

Diffraction of a Gaussian beam with a system of successively located optical wedges is considered. It is shown that the system is able to form higher-order optical vortices.

Determination of topological charges of polychromatic optical vortices

We introduce a simple, single beam method for determination of the topological charge of polychromatic optical vortices. It is based on astigmatic transformation of singular optical beams, where the intensity pattern of a vortex beam acquires a form of dark stripes in the focal plane of a cylindrical lens. The number of the dark stripes is equal to the modulus of the vortex topological charge, while the stripe tilt indicates the charge sign. We demonstrate experimentally the effectiveness of this technique by revealing complex topological structure of polychromatic singular beams.

Soliton bending and routing induced by interaction with curved surfaces in nematic liquid crystals

We study experimentally the interaction of spatial optical solitons with curved dielectric surfaces in unbiased nematic liquid crystals. We demonstrate that this interaction depends on the curvature of the surface and the walk-off, and it can be employed for efficient routing and control of the soliton trajectories. We also observe a large-angle total internal reflection of the soliton beam from an interface between liquid crystal and air.

Generation of single-charge optical vortices with an uniaxial crystal

We implement a novel experimental technique for generating mono- and polychromatic optical beams with on-axis single vortex by manipulating polarization singularities of light in birefringent crystals. We demonstrate that, in contrast to the well-known optical quadrupoles generated by beams propagating along the optical axis of a uniaxial crystal, the beam bearing isolated single-charge on-axis vortex can be generated if the incident beam is tilted with respect to the optical axis at a certain angle.