Optical Vortex Trap Research Articles

Aberration correction in holographic optical tweezers using a high-order optical vortex.

Holographic optical tweezers are a powerful optical trapping and manipulation tool in numerous applications such as life science and colloidal physics. However, imperfections in the spatial light modulator and optical components of the system will introduce detrimental aberrations to the system, thereby degrading the trapping performance significantly. To address this issue, we develop an aberration correction technique by using a high-order vortex as the correction metric. The optimal Zernike polynomial coefficients for quantifying the system aberrations are determined by comparing the distorted vortex and the ideal one. Efficiency of the proposed method is demonstrated by comparing the optical trap intensity distribution, trap stiffness, and particle dynamics in a Gaussian trap and an optical vortex trap, before and after aberration corrections.

Driven optical matter: Dynamics of electrodynamically coupled nanoparticles in an optical ring vortex.

To date investigations of the dynamics of driven colloidal systems have focused on hydrodynamic interactions and often employ optical (laser) tweezers for manipulation. However, the optical fields that provide confinement and drive also result in electrodynamic interactions that are generally neglected. We address this issue with a detailed study of interparticle dynamics in an optical ring vortex trap using 150-nm diameter Ag nanoparticles. We term the resultant electrodynamically interacting nanoparticles a driven optical matter system. We also show that a superior trap is created by using a Au nanoplate mirror in a retroreflection geometry, which increases the electric field intensity, the optical drive force, and spatial confinement. Using nanoparticles versus micron sized colloids significantly reduces the surface hydrodynamic friction allowing us to access small values of optical topological charge and drive force. We quantify a further 50% reduction of hydrodynamic friction when the nanoparticles are driven over the Au nanoplate mirrors versus over a mildly electrostatically repulsive glass surface. Further, we demonstrate through experiments and electrodynamics-Langevin dynamics simulations that the optical drive force and the interparticle interactions are not constant around the ring for linearly polarized light, resulting in a strong position-dependent variation in the nanoparticle velocity. The nonuniformity in the optical drive force is also manifest as an increase in fluctuations of interparticle separation, or effective temperature, as the optical driving force is increased. Finally, we resolve an open issue in the literature on periodic modulation of interparticle separation with comparative measurements of driven 300-nm-diameter polystyrene beads that also clearly reveal the significance of electrodynamic forces and interactions in optically driven colloidal systems. Therefore, the modulations in the optical forces and electrodynamic interactions that we demonstrate should not be neglected for dielectric particles and might give rise to some structural and dynamic features that have previously been attributed exclusively to hydrodynamic interactions.

基于纯相位液晶空间光调制器的全息光学捕获与微操纵

an improved and rapid three dimensional gerchberg-saxton (gs) algorithm based on the classic gs algorithm for computer generated holograms is proposed and applied to holographic optical tweezers. theoretical simulations and experimental results have demonstrated the rapidity and efficiency of the proposed algorithm. a robust holographic optical tweezers setup based on phase-only liquid-crystal spatial light modulator(slm) is built, and stable trapping and dynamic manipulation of yeast cells and silica beads with large array traps in three dimensions are demonstrated. two special traps, i.e., line trap with intensity gradient distribution and optical vortex trap, are generated to transport and rotate micro-particles respectively. the system is verified to be robust on particles manipulations, which provides a new and powerful tool for researches on biology, colloid physics and so on. © 2016, chinese laser press. all right reserved.

Collective excitations of hydrodynamically coupled driven colloidal particles.

Two colloidal particles, driven around an optical vortex trap, have been recently shown to pair due to an interplay between hydrodynamic interactions and the curved path they are forced to follow. We demonstrate here that this pairing interaction can be tuned experimentally, and we study its effect on the collective excitations of many particles driven around such an optical trap. We find that even though the system is overdamped, hydrodynamic interactions due to driving give rise to nondecaying excitations with characteristic dispersion relations. The collective excitations of the colloidal ring reflect fluctuations of particle pairs rather than those of single particles.

Theory of Optical Trapping by an Optical Vortex Beam

We propose a theory to explain optical trapping by optical vortices (OVs), which are emerging as important tools to trap mesoscopic particles. The common perception is that the trapping is solely due to the gradient force and that it may be characterized by three real force constants. However, we show that the OV trap can exhibit complex force constants, implying that the trapping must be stabilized by ambient damping. At different damping levels, particles exhibit remarkably different dynamics, such as stable trapping and periodic and aperiodic orbital motions.

Quantitative force mapping of an optical vortex trap

This paper describes the quantitative force mapping of micron-sized particles held in an optical vortex trap. We present a simple and efficient model, which accounts for the diffraction of the strongly localized optical field of the tightly focused laser beam, the spherical aberration introduced by the dielectric glass-to-water interface, employs the multidipole approximation for force calculations, and is able to reproduce, with quantitative agreement, the experimentally measured force map.

Controlled Shrinkage and Re-expansion of a Single Aqueous Droplet inside an Optical Vortex Trap

This paper describes the shrinkage and re-expansion of individual femtoliter-volume aqueous droplets that were suspended in an organic medium and held in an optical vortex trap. To elucidate the mechanism behind this phenomenon, we constructed a heat- and mass-transfer model and carried out experimental verifications of our model. From these studies, we conclude that an evaporation mechanism sufficiently describes the shrinkage of aqueous droplets held in a vortex trap, whereas a mechanism based on the supersaturation of the organic phase by water that surrounds the droplet adequately explains the re-expansion of the shrunk droplet. The proposed mechanisms correlated well with experimental observations using different organic media, when H2O was replaced with D2O and when an optical tweezer was used to induce droplet shrinkage rather than an optical vortex trap. For H2O droplets, the temperature rise within the droplet during shrinkage was on the order of 1 K or less, owing to the rapid thermal conduction of heat away from the droplet at the microscale and the sharp increase in solubility for water by the organic phase with slight elevations in temperature. Because most chemical species confined to droplets can be made impenetrable to the aqueous/organic interface, a change in the volume of aqueous droplets translates into a change in concentration of the dissolved species within the droplets. Therefore, this phenomenon should find use in the study of fundamental chemical processes that are sensitive to concentration, such as macromolecular crowding and protein nucleation and crystallization.

Anomalous collective dynamics in optically driven colloidal rings

Three fluid-borne colloidal spheres circulating around a ringlike optical vortex trap have been predicted to undergo periodic collective motion due to their hydrodynamic coupling. In fact, the quenched disorder in an experimentally projected optical vortex drives a transition to a dynamical state characterized by power-law divergence of phase-space trajectories and collective fluctuations characterized by noninteger exponents. The observed relationship between scaling in the microscopic trajectories and macroscopic collective fluctuations is consistent with predictions for the onset of weak chaos within the experimentally accessible time window.

Using Polarization-Shaped Optical Vortex Traps for Single-Cell Nanosurgery

Single-cell nanosurgery and the ability to manipulate nanometer-sized subcellular structures with optical tweezers has widespread applications in biology but so far has been limited by difficulties in maintaining the functionality of the transported subcellular organelles. This difficulty arises because of the propensity of optical tweezers to photodamage the trapped object. To address this issue, this paper describes the use of a polarization-shaped optical vortex trap, which exerts less photodamage on the trapped particle than conventional optical tweezers, for carrying out single-cell nanosurgical procedures. This method is also anticipated to find broad use in the trapping of any nanoparticles that are adversely affected by high-intensity laser light.

Vortex-Trap-Induced Fusion of Femtoliter-Volume Aqueous Droplets

This paper describes the use of an optical vortex trap for the transport and fusion of single femtoliter-volume aqueous droplets. Individual droplets were generated by emulsifying water in acetophenone with SPAN 80 surfactant. We demonstrate the ability of optical vortex traps to position trapped droplets precisely while excluding surrounding aqueous droplets from entering the trap, thereby preventing unwanted cross contamination by other nearby droplets. Additionally, the limitation of optical vortex traps for inducing droplet fusion is illustrated, and a remedy is provided through modulation of the spatial intensity profile of the optical vortex beam. Spatial modulation was achieved by translating the computer-generated hologram (CGH) with respect to the input Gaussian beam, thereby shifting the location of the embedded phase singularity (dark core) within the optical vortex beam. We present both simulated and experimentally measured intensity profiles of the vortex beam caused by translation of the CGH. We further describe the use of this technique to achieve controlled and facile fusion of two aqueous droplets.

Giant Colloidal Diffusivity on Corrugated Optical Vortices

A single colloidal sphere circulating around a periodically modulated optical vortex trap can enter a dynamical state in which it intermittently alternates between freely running around the ringlike optical vortex and becoming trapped in local potential energy minima. Velocity fluctuations in this randomly switching state still are characterized by a linear Einstein-like diffusion law, but with an effective diffusion coefficient that is enhanced by more than 2 orders of magnitude.

Simultaneous trapping of low-index and high-index microparticles observed with an optical-vortex trap

We report the first observation of the simultaneous three-dimensional confinement of both a low-index particle and a high-index particle within a single-beam optical trap by using a strongly focused laser beam containing an optical vortex. Experimental and theoretical investigations of the trap stability are described.

Trapping of low-index microparticles in an optical vortex

The equilibrium position of a low-index particle in an optical-vortex trap was experimentally measured for two different systems: a buoyant hollow glass sphere in water and a density-matched water droplet in acetophenone. Vortex traps are the only known static, single-beam configurations allowing three-dimensional trapping of such particles in the size range of 2–50 μm. The trap consists of a strongly focused Gaussian laser beam containing a holographically produced optical vortex. Using experimental and theoretical techniques, we also explored changes in the trapping efficiency owing to the vortex core size, the relative refractive index, and the numerical aperture of the focusing objective.