All-optical 3D atomic loops generated with Bessel light fields

The propagation invariance of Bessel beams as well as their transversal structure are used to perform a comparative analysis of their effect on cold atoms for four different configurations and combinations thereof. We show that, even at temperatures for which the classical description of the atom center of mass motion is valid, the interchange of momentum, energy and orbital angular momentum between light and atoms yields efficient tools for all-optical trapping, transporting and, in general, manipulating the state of motion of cold atoms.Comment: 13 pages, 9 figure

Polarization holograms allow highly efficient generation of complex light beams

We report a viable method to generate complex beams, such as the non-diffracting Bessel and Weber beams, which relies on the encoding of amplitude information, in addition to phase and polarization, using polarization holography. The holograms are recorded in polarization sensitive films by the interference of a reference plane wave with a tailored complex beam, having orthogonal circular polarizations. The high efficiency, the intrinsic achromaticity and the simplicity of use of the polarization holograms make them competitive with respect to existing methods and attractive for several applications. Theoretical analysis, based on the Jones formalism, and experimental results are shown

Particle-Size Effect in Airborne Standing-Wave Acoustic Levitation: Trapping Particles at Pressure Antinodes

It is well known that a particle put into an ultrasonic standing wave tends to move towards an equilibrium position, where the acoustic pressure-induced force on its surface compensates the particle weight. We demonstrate, by means of a full three-dimensional numerical analysis and a thorough experimental study, that the acoustic force, and thus the particle’s behavior, critically depends on its size. While particles within certain size ranges, including those smaller than half the wavelength, are trapped on axis around the pressure nodes, particles in other size ranges are trapped off axis nearby the pressure antinodes. This behavior, related with sign inversions of the radiation force, implies that the magnitude of the force, and thus the trapping stiffness, can be maximum or null for some specific sizes. As a case of study, we analyze expanded polystyrene particles levitated in air with an ultrasonic frequency of 40 kHz, a relevant system due to recent applications for the development of volumetric displays. Yet, our results illustrate a general behavior of radiation-based traps with structured wave fields

Attractive-repulsive dynamics on light-responsive chiral microparticles induced by polarized tweezers3

ab Multifunctional colloidal micro and nano-particles with controlled architectures have very promising properties for applications in bio and nanotechnologies. Here we report on the unique dichotomous dynamical behaviour of chiral spherical microparticles, either fluid or solid, manipulated by polarized optical tweezers. The particles are created using a reactive mesogen mixed with a chiral dopant to form cholesteric liquid crystal droplets in water emulsion. The photopolymerization enables the chiral supramolecular configurations to be frozen in solid particles. Different internal architectures in the supramolecular structures, guided by the interfacial chemistry, enable optically isotropic or anisotropic spherical objects to be obtained. For particles having radial configuration of the cholesteric helices, we show that light can exert either a repulsive or attractive force depending on the handedness of its circular polarization, due to the unique selective reflection property of the cholesteric phase. On the other hand, very exotic dynamics is observed in the case of anisotropic chiral particles. Depending on the light handedness, they behave like Janus spherical particles with dissimilar optical properties, meaning that the surface of the dielectric particles is partly transparent and partly reflecting. We foresee interesting potential applications in micro and optofluidics, microphotonics and materials science

Visualization 1: 3D micromanipulation at low numerical aperture with a single light beam: the focused-Bessel trap

Video showing three different particles trapped by the FBT Originally published in Optics Letters on 01 February 2016 (ol-41-3-614

Particle-Size Effect in Airborne Standing-Wave Acoustic Levitation: Trapping Particles at Pressure Antinodes

International audienceIt is well known that a particle put into an ultrasonic standing wave tends to move towards an equilibrium position, where the acoustic pressure-induced force on its surface compensates the particle weight. We demonstrate, by means of a full three-dimensional numerical analysis and a thorough experimental study, that the acoustic force, and thus the particle's behavior, critically depends on its size. While particles within certain size ranges, including those smaller than half the wavelength, are trapped on axis around the pressure nodes, particles in other size ranges are trapped off axis nearby the pressure antinodes. This behavior, related with sign inversions of the radiation force, implies that the magnitude of the force, and thus the trapping stiffness, can be maximum or null for some specific sizes. As a case of study, we analyze expanded polystyrene particles levitated in air with an ultrasonic frequency of 40 kHz, a relevant system due to recent applications for the development of volumetric displays. Yet, our results illustrate a general behavior of radiation-based traps with structured wave fields

Observation of Polarization Singularities and Topological Textures in Sound Waves

International audienc