Two-dimensional Optical Trapping Research Articles

Precise position and angular control of optical trapping and manipulation via a single vortex-pair beam

Optical trapping and manipulation using structured laser beams now attract increasing attention in many areas including biology, atomic science, and nanofabrication. Here we propose and demonstrate experimentally the use of a single vortex-pair beam in two-dimensional optical trapping and manipulation. Using the focal properties of such vortex-pair beams, we successfully manipulate two spherical microparticles simultaneously, and obtain the precise position-control on the microparticles by adjusting the off-axis parameter a of the vortex-pair beam. Furthermore, we also realize the high-precision angular-controllable rotation of cylindrical microrods by rotating the initial phase structure of such vortex-pair beams, which is like an optical wrench due to two focused bright spots at the focal plane of objective lens. Our experimental result provides an alternative manipulation of microparticles and may have potential applications in biological area, and optically driven micromachines or motors.

All-dielectric silicon metalens for two-dimensional particle manipulation in optical tweezers

Dynamic control of compact chip-scale contactless manipulation of particles for bioscience applications remains a challenging endeavor, which is restrained by the balance between trapping efficiency and scalable apparatus. Metasurfaces offer the implementation of feasible optical tweezers on a planar platform for shaping the exerted optical force by a microscale-integrated device. Here we design and experimentally demonstrate a highly efficient silicon-based metalens for two-dimensional optical trapping in the near-infrared. Our metalens concept is based on the Pancharatnam–Berry phase, which enables the device for polarization-sensitive particle manipulation. Our optical trapping setup is capable of adjusting the position of both the metasurface lens and the particle chamber freely in three directions, which offers great freedom for optical trap adjustment and alignment. Two-dimensional (2D) particle manipulation is done with a relatively low-numerical-aperture metalens ( NA ML = 0.6 ). We experimentally demonstrate both 2D polarization-sensitive drag and drop manipulation of polystyrene particles suspended in water and transfer of angular orbital momentum to these particles with a single tailored beam. Our work may open new possibilities for lab-on-a-chip optical trapping for bioscience applications and microscale to nanoscale optical tweezers.

Two-dimensional optical trapping and clustering of magnetic nanoparticles

The dynamics of Fe3O4 magnetic nanoparticles under the irradiation of a tightly focused laser beam was investigated by using a dark-field microscope. It was found that the magnetic nanoparticles were pushed away from the laser spot by the optical scattering force and the absorption force when the laser focus was located between the two cover slips of the sample cell. A depletion region of magnetic nanoparticles was formed in the laser spot. However, when the focus of the laser was located at the bottom of the upper cover slip of the sample cell, the magnetic nanoparticles could be trapped by the optical forces combined with the opposite force of the upper cover slip and formed magnetic clusters. In addition, the evolution of the incandescent light transmission spectrum of the magnetic fluid under the irradiation of the 532 nm laser with different powers was studied. It was observed that the intensity of the transmission spectrum of the incandescent light decreased and the peak wavelength of the transmission spectrum shifted towards the longer wavelength with the increase of the laser power.

Optical trap formation with a four-channel liquid crystal light modulator

Experiments on the dynamic control of two-dimensional optical trap spatial structure and manipulation of micron-sized dielectric particles are performed with a four-channel liquid crystal modulator. Tweezers with this device can execute the trapping of a single particle and its subsequent relocation along the square trajectory. Also, when shaped as a line segment, the trap can capture several particles and rotate them. Therefore, it is experimentally proven that for certain tasks this device can be a compact and technologically simple alternative to the available commercial multi-pixel liquid crystal modulators.

Silicon-on-insulator multimode-interference waveguide-based arrayed optical tweezers (SMART) for two-dimensional microparticle trapping and manipulation

We demonstrate two-dimensional optical trapping and manipulation of 1 μm and 2.2 μm polystyrene particles in an 18 μm-thick fluidic cell at a wavelength of 1565 nm using the recently proposed Silicon-on-insulator Multimode-interference (MMI) waveguide-based ARrayed optical Tweezers (SMART) technique. The key component is a 100 μm square-core silicon waveguide with mm length. By tuning the fiber-coupling position at the MMI waveguide input facet, we demonstrate various patterns of arrayed optical tweezers that enable optical trapping and manipulation of particles. We numerically simulate the physical mechanisms involved in the arrayed trap, including the optical force, the heat transfer and the thermal-induced microfluidic flow.

Revisit on dynamic radiation forces induced by pulsed Gaussian beams

Motivated by the recent optical trapping experiments using ultra-short pulsed lasers [Opt. Express 18, 7554 (2010); Appl. Opt. 48, G33 (2009)], in this paper we have re-investigated the trapping effects of the pulsed radiation force (PRF), which is induced by a pulsed Gaussian beam acting on a Rayleigh dielectric sphere. Based on our previous model [Opt. Express 15, 10615 (2007)], we have considered the effects arisen from both the transverse and axial PRFs, which lead to the different behaviors of both velocities and displacements of a Rayleigh particle within a pulse duration. Our analysis shows that, for the small-sized Rayleigh particles, when the pulse has the large pulse duration, it might provide the three-dimensional optical trapping; and when the pulse has the short pulse duration, it only provides the two-dimensional optical trapping with the axial movement along the pulse propagation. When the particle is in the vacuum or in the situation with the very weak Brownian motion, the particle can always be trapped stably due to the particle's cumulative momentum transferred from the pulse, and only in this case the trapping effect is independent of pulse duration. Finally, we have predicted that for the large-sized Rayleigh particles, the pulse beam can only provide the two-dimensional optical trap (optical guiding). Our results provide the important information about the trapping mechanism of pulsed tweezers.

Theoretical Study of a Two-Dimensional Optical Trapping of a Microsphere by the Laser Beam from an Optical Fiber end Inserted into a Sample Cell at an Angle.

Optical forces exerted on a microsphere by the laser beam from an optical fiber inserted at an angle were theoretically analyzed. From these results, we verified that the laser beam emitted at an angle from an optical fiber could obtain a two-dimensional optical trapping of a microsphere on the surface of a sample cell.

Optical Force on a Micro-Sphere by the Laser Beam from a Lensed Optical Fiber Inserted at an Angle

Optical forces acting on a micro-sphere were studied to corroborate the single-beam fiber optic trap. Transverse optical force acted to pull the micro-sphere back to the beam axis, but axial force always acted in the direction away from the optical fiber end because the laser beam from optical fiber could not be strongly focused. A stable two-dimensional optical trapping could be obtained by the weakly focused laser beam from the fiber end inserted at an angle.