Optical trapping and arrangement with reconfigurable "bottle" beam for digital holographic microscopy

N V Shostka, B N Sokolenko, O S Karakcheva, D A Poletaev, A O Titova, A V Prisyazhniuk and I A Ismailov

The design and construction of optical tweezers based on uniaxial crystal anisotropy for generation of adjustable "bottle" beam trap carrying optical vortex with orbital angular momentum is considered. In coupling with digital holographic microscopy, optical trapping becomes a high precision instrument for visualization, shape definition and refractivity measurements of isolated micro structures and biological objects in-situ. The non-destructive and sterile non-contact tweezing of specimens or their parts in localized intensity minima of coherent vortex beam was performed with using of 200 mW semiconductor 532 nm trapping laser and LiNbO3 crystal. Visualization and position control of trapped marine centric diatoms was performed by a lens-free axial digital holographic microscopy in liquid medium.

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Impact of the evanescent waves on the backflow of power in the near field

V V Kotlyar, A A Kovalev and D S Kalinkina

For an elliptically polarized optical vortex with an arbitrary integer topological charge, using the expressions for all six components of the electric and magnetic field strength vectors, we obtain an expression for the longitudinal component of the Poynting vector in the initial plane. For the particular case of a narrow angular spectrum of plane waves (Bessel beam) and for the circular polarization, it is shown that in the presence of the inhomogeneous evanescent waves in the initial light field, a reverse flux of light energy can occur near the op-tical axis. It is shown that this reverse energy flux is due to toroidal vortices in the longitudinal plane.

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Effect of small forces on microsphere under optical trap

Rajesh Kumar, Lalit M Bharadwaj and Arun K Lall

In this era of technological development, greater impact of nanotechnology now can be seen in many fields due to better properties and precise control. Many functions are being executed by bio nano-materials or biomolecules in living systems in a very efficient manner. The functional behaviour and their properties need to be examined to use them for various nano-device applications. The mechanical properties of the biomolecules can be studied by attaching them with microspheres and measuring forces on these microspheres through optical trap. Microspheres of three-micrometer diameter were trapped at the focus of infrared laser and viscous drag forces were applied to measure the effect of these forces on the trapped microsphere. It was observed that with 28mW intensity Laser, the trapped microsphere was displaced by 0.19 μm at 2.1 pN force and trap stiffness was determined as 0.011pN/nm. The findings can be useful while attaching these microspheres as cargos along the bionanomotors for nanorobotics and drug delivery applications.

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Positioning of space objects by laser-induced jets

E Y Loktionov and D S Sitnikov

Laser-induced thrust provides a number of significant advantages over the currently used methods: virtually any material can be used as a working medium; radiation source and its power unit can be located outside the spacecraft; it is possible to provide a minimum impulse bit of 1 nN s or less; momentum imparted at single impact can be controlled within 2 orders of magnitude dynamic range. We have considered recoil momentum generation at femtosecond to continuous laser impact range on different materials normalized by laser output performance to evaluate momentum coupling to on-board energy system. It is shown that better momentum coupling at short wavelength is not worth of associated energy losses, but laser pulse shortening to picosecond range is. Data reported here on laser thrust generation efficiency and methods of laser impact layout are of interest not for small spacecraft application range broadening only, but also for the prevention of emergency situations development (launch to unplanned orbit, uncontrolled rotation, etc.), space debris removal, and anti-asteroid protection of the Earth – possible impact layouts for such missions are considered.

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Dynamics analysis of nanoparticles optically driven by a Laguerre-Gaussian beam with optical spin

Mamoru Tamura, Takashige Omatsu and Takuya Iida

We theoretically discover that the spin angular momentum (SAM) enables to modulate the orbital torque through the inter-particle light-induced force (IP-LIF). Laguerre - Gaussian beam with the orbital angular momentum (OAM) can induce the orbital motion for the optically trapped objects. In addition, the SAM can also accelerate or decelerate the orbital motion due to the IP-LIF. Our discovery provides a new physical aspect, i.e. the IP-LIF plays an important role in the many-body dynamics of nanoparticles via the SAM-OAM coupling.

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Formation of a single poly(N,N-diethylacrylamide) micro-droplet in water by coupling of photothermal effects and an optical force

M Matsumoto, T Asoh, T Shoji, T Nishiyama, Hideo Horibe, Yukiteru Katsumoto and Yasuyuki Tsuboi

Poly(N-isopropylacrylamide) (PNIPAM) exhibits phase separation with lower critical solution temperature (LCST). In the 1990s, Masuhara and co-workers reported the first demonstration of optical trapping of PNIPAM forming a micrometer-sized polymer droplet. Since then, this technique has attracted much attention to create a molecular assembly in a microspace. In the present study, we targeted poly(N,N-diethylacrylamide) (PDEA), which has an analogous chemical structure to PNIPAM. We demonstrated that optical tweezers formed the unique micro-morphologies of a phase separated PDEA droplet. Fluorescence microscopic images and Raman spectra of the PDEA droplet showed that a lot of smaller-sized water-rich micro-domains were inhomogeneously formed in the droplet. Such unique phase separation behavior was never observed in steady-state heating of an aqueous PDEA solution above its LCST. Our results indicate that a novel micro-structure can be formed by coupling of an optical gradient force and a local temperature elevation.

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Detection of optical force due to multiphoton absorption

S Nakamura, R Sunakawa, K Setoura, S Ito and H Miyasaka

Resonant optical manipulation using absorption force so far has been based on the linear (one-photon) absorption by target material, while optical forces due to multiphoton absorption have not been much investigated. As multiphoton absorption obeys different selection rule from that of one-photon absorption, and also shows non-linear dependence on light intensity, a larger variety of photo-mechanical responses of small particles can be expected by using multiphoton absorption force. In this study, we focused femtosecond laser pulses to a single polymer microparticle containing fluorescence dyes to exert multiphoton absorption force on the particle. We successfully observed the three-dimensional motion of the photo-irradiated microparticle due to the multiphoton absorption.

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Time-scale dependent Brownian motion of nanoparticles in clusters at a solid-liquid interface by laser trapping

Itsuo Hanasaki and Chie Hosokawa

Nanoparticles in a cluster trapped by laser-induced force field show Brownian motion at solid-liquid interfaces. The cluster formation means that the particles are highly concentrated. In general, the diffusion coefficients of particles in fluids decrease with substantially high concentration and also in the vicinity of solid walls due to the hydrodynamic effect. The particle trajectory data obtained from the experimental measurements show that the longer time span of observation leads to smaller diffusion coefficient due to the confinement effect. However, they also exhibit higher diffusion coefficient compared to the the bulk condition when evaluated at a sufficiently short time span of the frame interval under the condition of sufficiently high laser powers.

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Anisotropic dynamics of nanoparticles in clusters at a solid-liquid interface by laser trapping

Itsuo Hanasaki and Chie Hosokawa

It is well-recognized that the Brownian motion of particles in fluids is random. Nevertheless, there can be characteristics depending on the specific physical conditions. We analyze the system of nanoparticle clusters formed by the laser trapping force field at the solid-liquid interface, based on the microscopy movie data. Since the laser trapping force field is basically a function of radial distance from the focal point in the two dimension at the liquid-solid interface, we examine the difference of displacement distributions in the radial and circumferential directions. The results show that the basic characteristics in this system depends on the laser power, and there is an anisotropy in the stochastic motion of the nanoparticles.

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Plasmonic optical trapping of pyrene-pendant polymer chains by controlling thermophoretic force

Kenta Ushiro, Tatsuya Shoji and Yasuyuki Tsuboi

Plasmonic optical tweezers (POT) has a high potential for manipulation of nanomaterials due to an enhanced optical force. However, unfavorable thermal effects induced by plasmon excitation have frequently hindered the manipulation. For this issue, we have recently developed a novel non-plasmonic optical tweezers using a nanostructured silicon substrate (B-Si). We called it "Nano-Structured Semi-Conductor-Assisted Optical Tweezers (NASSCA-OT)". In the present study, we trapped pyrene-pendant polymer chains homogeneously dissolved in water for POT or NASSCA-OT. We used plasmonic gold nanopyramidal dimer arrays or B-Si in contact with the aqueous polymer solution. During plasmon excitation with a near-infrared laser light, any sign of optical trapping was never detected in fluorescence micro-spectroscopy. By contrast, trapping of the polymer chains was obviously observed for NASSCA-OT. Upon laser irradiation, pyrene excimer fluorescence was dramatically increased at the focal spot. These results indicate that NASSCA-OT is a powerful tool for manipulation of molecular materials.

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Numerical calculation and Cartesian multipole decomposition of optical pulling force acting on Si nanocube in visible region

E.A. Gurvitz and A. S. Shalin

The multipole decomposition of optical force and scattering cross-section is considered for the two plane waves incident on Si nanocube. The obtained results show the high impact of a toroidal moment and high order multipoles in optical force, while they aren't represented main resonances in scattering cross-section.

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Lateral radiative forces exerted by evanescent fields along a hyperbolic metamaterial slab

I S Nefedov, C A Valagiannopoulos and A S Shalin

We show and investigate the optical forces acting on a particle in the vicinity of a planar waveguide which is filled with hyperbolic material and supports propagation across its plane (two-dimensional). The anisotropy axis of its medium lies in plane of the waveguide. In contrast to commonly considered pushing or pulling forces, acting in one-dimensional guiding structures, in the case of two-dimensional wave propagation, the angles between the momentum and the total energy flow may take any value around the circle. Accordingly, evanescent fields out of the slab exert lateral radiative forces on a nanoparticle oriented parallel to momentum being controllably different from the total energy flow direction. This provides a flexibility in manipulation by nanoparticles by employing suitably engineered hyperbolic structures.

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Tractor beams at metamaterial substrates

A Ivinskaya, N Kostina, M I Petrov, A A Bogdanov, S Sukhov, P Ginzburg and A S Shalin

Optical forces acting on nanoobjects can be enhanced, inverted or cancelled out by the presence of carefully chosen environment. Here we consider metamaterial substrate which can modify optical forces through the excitation of surface waves and volumetric hyperbolic modes. Both types of interaction channels will be discussed in the present work where we show new effect of pulling forces on subwavelength dielectric particles above multilayer hyperbolic substrates.

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Experimental stochastic systems based on optical forces

Oto Brzobohaty, Stephen Simpson, Martin Siler, Petr Jakl, Jana Damkova, Vojtech Svak, Alejandro Arzola, Karen Volke-Sepulveda, Radim Filip and Pavel Zemanek

We will present our recent theoretical and experimental results related to the behaviour of micro- and nanoparticle placed into nonlinear optical potentials under overdamped or underdamped regime. The two-dimensional optical ratchet rectifies motion of Brownian particles in any direction in the plane, unstable cubic optical potential results in noise-induced particle motion and action of non-conservative optical spin-force leads to orbiting of a levitated particle.

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The zoo of nonconservative optical forces

S V Sukhov

Optical forces are usually described as conservative ones originating from intensity gradients in optical tweezers. However, the fundamental optical action on matter is nonconservative. In contrast to gradient forces, the spectrum of action of nonconservative forces is much wider: they can propel, pull, rotate objects or move objects along complicated trajectories. Different manifestations of nonconservative optical forces will be reviewed and their dependence on the specific spatial properties of optical fields will be discussed. New developments relevant to the nonconservative optical forces such as negative forces (tractor beams) and transversal forces will also be discussed.

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Optical forces in optical nanofibers

Y Zhang, H Yu and Z Li

Optical forces exerted upon the endface of optical nanofiber have been carefully investigated numerically. Detailed spatial optical force distributions along the fiber axis are obtained. Dependence of optical force on fiber diameters, input modal polarizations, oblique-cut endfaces are carefully taken into considerations. It is clear now that oblique-cut fiber endface should be responsible for sideways deflection of nanofiber.

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The motion of nanoparticles under the non-conservative forces mediated by surface plasmon polaritons

I D Toftul, A A Bogdanov and M I Petrov

We have developed the theoretical and numerical modelling of nanoparticle dynamics near planar metallic interface under light radiation. Using our model, we employed the Green's function formalism to simulate the dynamics of nanoparticles under the action of surface plasmon polariton mediated optical forces. By varying the illumination conditions, we determined the different regimes of motion, such as surface attraction and repulsion, and optical pulling regime. We showed that the topology of the trajectories dramatically change, when the surface plasmon polaritons are excited.

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Torque Induced on Lipid Microtubules with Optical Tweezers

T Na wichean, S Charrunchon, A Pattanaporkratana, J Limtrakul and N Chattham

Chiral Phospholipids are found self-assembled into cylindrical tubules of 500 nm in diameter by helical winding of bilayer stripes under cooling in ethanol and water solution. Theoretical prediction and experimental evidence reported so far confirmed the modulated tilt direction in a helical striped pattern of the tubules. This molecular orientation morphology results in optically birefringent tubules. We investigate an individual lipid microtubule under a single optical trap of 532 nm linearly polarized laser. Spontaneous rotation of a lipid tubule induced by radiation torque was observed with only one sense of rotation caused by chirality of a lipid tubule. Rotation discontinued once the high refractive index axis of a lipid tubule aligned with a polarization axis of the laser. We further explored a lipid tubule under circularly polarized optical trap. It was found that a lipid tubule was continuously rotated confirming the tubule birefringent property. We modified the shape of optical trap by cylindrical lens obtaining an elliptical profile optical trap. A lipid tubule can be aligned along the elongated length of optical trap. We reported an investigation of competition between polarized light torque on a birefringent lipid tubule versus torque from intensity gradient of an elongated optical trap.

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Low-loss nanowire and nanotube plasmonic waveguide with deep subwavelength light confinement and enhanced optical trapping forces

Xiaogang Chen, Qijing Lu, Xiang Wu, Hongqin Yang and Shusen Xie

With the rapid development of the micro/nano fabrication technology, the semiconductor nanowires and nanotubes with size and dimensions controllable realize wide applications in nanophotonics. In this talk, we propose two kinds of hybrid plasmonics waveguides, one is consisting of nanowires, another is consisting of nanotubes. By employing the simulating with different geometric parameters, the basic waveguiding properties, including the effective mode area, the propagation length, the mode character and the optical trapping forces can be achieved. Compared with previous plasmonic waveguide with plane metal substrate, current plasmonics waveguides with ease of fabrication have the advantage of long propagation length and effectively optical trapping of nanoparticles with deep subwavelength light confinement, which may be very useful for nanophotonic integrated circuits, nanolasers and biosensing.

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Femtosecond scalpel-optical tweezers: efficient tool for assisted hatching and trophectoderm biopsy

D S Sitnikov, I V Ilina, Yu V Khramova, M A Filatov and M L Semenova

Ultrashort laser pulses have enabled highly precise and delicate processing of biological specimens. We present the results of using femtosecond (fs) laser pulses for dissection of zona pellucida (ZP) in mouse embryos during assisted hatching procedure and for trophectoderm biopsy as well. We studied the effects of application of fs laser radiation in the infrared (1028 nm) and visible (514 nm) wavelength ranges. Laser irradiation parameters were optimized so as not to compromise the viability of the treated embryos. Embryo biopsy was carried out in late-stage mouse preimplantation embryos. Femtosecond laser pulses were applied to detach the desired amount of trophectoderm cells from the blastocyst, while the optical tweezers trapped the cells and moved them out of the embryo. The parameters of laser radiation were optimized so as to efficiently perform embryo biopsy and preserve the viability of the treated embryos. The thermal effects can be significantly lower when fs lasers are used as compared to CW or long-pulse lasers. It is crucial when dealing with living cells or organisms.

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