Raul Josue Hernandez

Chiral self-assembled solid microspheres: a novel multifunctional microphotonic device.

Solid chiral microspheres with unique and multifunctional optical properties are produced from cholesteric liquid crystal-water emulsions using photopolymerization processes. These self-organizing microspheres exhibit different internal configurations of helicoidal structures with radial, conical or cylindrical geometries, depending on the physicochemical characteristics of the precursor liquid crystal emulsion.

Chiral resolution of spin angular momentum in linearly polarized and unpolarized light

Linearly polarized (LP) and unpolarized (UP) light are racemic entities since they can be described as superposition of opposite circularly polarized (CP) components of equal amplitude. As a consequence they do not carry spin angular momentum. Chiral resolution of a racemate, i.e. separation of their chiral components, is usually performed via asymmetric interaction with a chiral entity. In this paper we provide an experimental evidence of the chiral resolution of linearly polarized and unpolarized Gaussian beams through the transfer of spin angular momentum to chiral microparticles. Due to the interplay between linear and angular momentum exchange, basic manipulation tasks, as trapping, spinning or orbiting of micro-objects, can be performed by light with zero helicity. The results might broaden the perspectives for development of miniaturized and cost-effective devices.

Cholesteric solid spherical microparticles: chiral optomechanics and microphotonics

ABSTRACT This article reviews the main results from the investigations performed on solid chiral microparticles based on polymerized cholesteric droplets. The procedures of particles generation, the structural characterization, optomechanics and microphotonics investigations are shown. The aim of this work is to give a picture of the innovation introduced by exploring the combination of chirality, self-organization and solid structure.

Magnus force effect in optical manipulation

The effect of the Magnus force in optical micromanipulation has been observed. An ad hoc experiment has been designed based on a one-dimensional optical trap that carries angular momentum. The observed particle dynamics reveals the occurrence of this hydrodynamic force, which is neglected in the common approach. Its measured value is larger than the one predicted by the existing theoretical models for micrometric particles and low Reynolds number, showing that the Magnus force can contribute to unconventional optohydrodynamic trapping and manipulation.

Light-induced rotations of chiral birefringent microparticles in optical tweezers.

We study the rotational dynamics of solid chiral and birefringent microparticles induced by elliptically polarized laser light in optical tweezers. We find that both reflection of left circularly polarized light and residual linear retardance affect the particle dynamics. The degree of ellipticity of laser light needed to induce rotations is found. The experimental results are compared with analytical calculations of the transfer of angular moment from elliptically polarized light to chiral birefringent particles.

Self-Organized Chiral Microspheres

A variety of chiral microspheres, each one possessing distinctive configurations of the molecular director, are studied. The process to obtain the solid particles is illustrated and some of their optical features is discussed. The optical properties of these objects depend from the emulsion preparation standards. The self-organized structures have been tailored by means of both the chiral dopant concentration and the molecular anchoring at the surface. The microspheres reveal exciting optical properties, i.e. they show specific kinds of selective reflection that can be sorted as radial, conical and cylindrical. The features of these micro-photonic devices are confirmed through experiments of polarized optical manipulation and laser emission. These complex structures constitute very peculiar micro-systems, inspiring attractive technological applications.

Lasing from chiral doped nematic liquid crystal droplets generated in a microfluidic device

ABSTRACT Microfluidics generated liquid crystal (LC) droplets are currently used as microresonators in optofluidics applications due to their small size, narrow droplets diameter distributions, high Q-factor and tunability properties. In this work we report a short review regarding lasing from cholesteric liquid crystals (CLCs) confined in spherical microdroplets generated in a thermally stabilized environment by using a microfluidic technique. The photonic bandgaps (PBGs) have been theoretically calculated and experimentally measured as a function of temperature. A wide tuning effect of hundreds of nanometers has been experimentally observed for the main PBG and reported for two different concentrations of the chiral dopant used to give chirality to the nematic LC. A single-droplet lasing effect has been reported and optimized by using a stop flow technique and the dynamic of the reorientation inside the droplets observed under a polarized optical microscope integrated into the experimental setup.

Chiral particles in the dual-beam optical trap

We investigate the dynamics of chiral microparticles in a dual-beam optical trap. The chiral particles have the structure of spherical chiral microresonators, with a reflectance deriving from the supramolecular helicoidal arrangement. Due to the strong asymmetric response of the particles to light with a specific helicity and wavelength, their trapping position and rotational frequency can be controlled by proper combination of the polarization state of the two light beams. Here symmetric and asymmetric polarization configurations of dual- interfering beam traps have been investigated. Based on the polarization controlled asymmetric transmission of the chiral particles, a tunable wash-board potential is created enabling the control of the trapping position along the beams axis. Asymmetric configurations display polarization controlled rotation of the trapped particles. Optical binding of rotating particles exhibits a complex dynamics.