Glen R Kirkham, James Ware, Thomas Upton, Stephanie Allen, Kevin M Shakesheff, Lee DK Buttery
Three-dimensional (3D) cell models that mimic the structure and function of native tissues are enabling more detailed study of physiological and pathological mechanisms in vitro. We have previously demonstrated the ability to build and manipulate 3D multicellular microscopic structures using holographic optical tweezers (HOTs). Here, we show the construction of a precisely patterned 3D microenvironment and biochemical gradient model consisting of mouse embryoid bodies (mEBs) and polymer microparticles loaded with retinoic acid (RA), embedded in a hydrogel. We demonstrate discrete, zonal expression of the RA-inducible protein Stra8 within mEBs in response to release of RA from polymer microparticles, corresponding directly to the defined 3D positioning of the microparticles using HOTs. These results demonstrate the ability of this technology to create chemical microgradients at definable length scales and to elicit, with fidelity and precision, specific biological responses. This technique can be used in the study of in vitro microenvironments to enable new insights on 3D cell models, their cellular assembly, and the delivery of drug or biochemical molecules for engineering and interrogation of functional and morphogenic responses.
DOI
Friday, September 27, 2019
Artificial Cell Membranes Interfaced with Optical Tweezers: A Versatile Microfluidics Platform for Nanomanipulation and Mechanical Characterization
Aurora Dols-Perez, Victor Marin, Guillermo J. Amador, Roland Kieffer, Daniel Tam, Marie-Eve Aubin-Tam
Cell lipid membranes are the site of vital biological processes, such as motility, trafficking, and sensing, many of which involve mechanical forces. Elucidating the interplay between such bioprocesses and mechanical forces requires the use of tools that apply and measure piconewton-level forces, e.g., optical tweezers. Here, we introduce the combination of optical tweezers with free-standing lipid bilayers, which are fully accessible on both sides of the membrane. In the vicinity of the lipid bilayer, optical trapping would normally be impossible due to optical distortions caused by pockets of the solvent trapped within the membrane. We solve this by drastically reducing the size of these pockets via tuning of the solvent and flow cell material. In the resulting flow cells, lipid nanotubes are straightforwardly pushed or pulled and reach lengths above half a millimeter. Moreover, the controlled pushing of a lipid nanotube with an optically trapped bead provides an accurate and direct measurement of important mechanical properties. In particular, we measure the membrane tension of a free-standing membrane composed of a mixture of dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) to be 4.6 × 10–6 N/m. We demonstrate the potential of the platform for biophysical studies by inserting the cell-penetrating trans-activator of transcription (TAT) peptide in the lipid membrane. The interactions between the TAT peptide and the membrane are found to decrease the value of the membrane tension to 2.1 × 10–6 N/m. This method is also fully compatible with electrophysiological measurements and presents new possibilities for the study of membrane mechanics and the creation of artificial lipid tube networks of great importance in intra- and intercellular communication.
DOI
Cell lipid membranes are the site of vital biological processes, such as motility, trafficking, and sensing, many of which involve mechanical forces. Elucidating the interplay between such bioprocesses and mechanical forces requires the use of tools that apply and measure piconewton-level forces, e.g., optical tweezers. Here, we introduce the combination of optical tweezers with free-standing lipid bilayers, which are fully accessible on both sides of the membrane. In the vicinity of the lipid bilayer, optical trapping would normally be impossible due to optical distortions caused by pockets of the solvent trapped within the membrane. We solve this by drastically reducing the size of these pockets via tuning of the solvent and flow cell material. In the resulting flow cells, lipid nanotubes are straightforwardly pushed or pulled and reach lengths above half a millimeter. Moreover, the controlled pushing of a lipid nanotube with an optically trapped bead provides an accurate and direct measurement of important mechanical properties. In particular, we measure the membrane tension of a free-standing membrane composed of a mixture of dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) to be 4.6 × 10–6 N/m. We demonstrate the potential of the platform for biophysical studies by inserting the cell-penetrating trans-activator of transcription (TAT) peptide in the lipid membrane. The interactions between the TAT peptide and the membrane are found to decrease the value of the membrane tension to 2.1 × 10–6 N/m. This method is also fully compatible with electrophysiological measurements and presents new possibilities for the study of membrane mechanics and the creation of artificial lipid tube networks of great importance in intra- and intercellular communication.
DOI
Plasmonic gold nanoparticles: Optical manipulation, imaging, drug delivery and therapy
Majid Sharifi, Farnoosh Attar, Ali Akbar Saboury, Keivan Akhtari, Nasrin Hooshmand, Anwarul Hasan, Mostafa A.El-Sayed, Mojtaba Falahati
Over the past two decades, the development of plasmonic nanoparticle (NPs), especially gold (Au) NPs, is being pursued more seriously in the medical fields such as imaging, drug delivery, and theranostic systems. However, there is no comprehensive review on the effect of the physical and chemical parameters of AuNPs on their plasmonic properties as well as the use of these unique characteristic in medical activities such as imaging and therapeutics. Therefore, in this literature the surface plasmon resonance (SPR) modeling of AuNPs was accurately captured toward precision medicine. Indeed, we investigated the importance of plasmonic properties of AuNPs in optical manipulation, imaging, drug delivery, and photothermal therapy (PTT) of cancerous cells based on their physicochemical properties. Finally, some challenges regarding the commercialization of AuNPs in future medicine such as, cytotoxicity, lack of standards for medical applications, high cost, and time-consuming process were discussed.
DOI
Over the past two decades, the development of plasmonic nanoparticle (NPs), especially gold (Au) NPs, is being pursued more seriously in the medical fields such as imaging, drug delivery, and theranostic systems. However, there is no comprehensive review on the effect of the physical and chemical parameters of AuNPs on their plasmonic properties as well as the use of these unique characteristic in medical activities such as imaging and therapeutics. Therefore, in this literature the surface plasmon resonance (SPR) modeling of AuNPs was accurately captured toward precision medicine. Indeed, we investigated the importance of plasmonic properties of AuNPs in optical manipulation, imaging, drug delivery, and photothermal therapy (PTT) of cancerous cells based on their physicochemical properties. Finally, some challenges regarding the commercialization of AuNPs in future medicine such as, cytotoxicity, lack of standards for medical applications, high cost, and time-consuming process were discussed.
DOI
Nanotraffic Lights: Rayleigh Scattering Microspectroscopy of Optically Trapped Octahedral Gold Nanoparticles
Tatsuya Shoji, Mamoru Tamura, Tatsuya Kameyama, Takuya Iida, Yasuyuki Tsuboi, Tsukasa Torimoto
We demonstrate a pronounced color change in the light scattered from thermally fluctuating optically trapped octahedral gold nanoparticles (OGPs) in water using a tightly focused near-infrared laser beam. Monodispersed OGPs with an average edge length of 67 ± 6.5 nm were synthesized using a polyol method. Using dark-field microscopy, we observed successive changes of color (i.e., red → green → yellow) scattered from the trapped OGPs. We analyzed this trapping behavior by means of Rayleigh scattering microspectroscopy and concluded that pairs of OGPs trapped in the potential well interact with each other to form dimers oriented in the direction of the electric field vector of the trapping laser light. We theoretically obtained the absorption and scattering cross sections and the enhancement factors of the electric field of an OGP dimer in three different configurations by means of finite-difference time-domain calculations. The calculations suggest that the dimers become preferentially oriented in a vertex-to-vertex configuration because of the high polarizability. These findings indicate that optical tweezers are a promising technique for creating highly ordered assemblies of plasmonic nanostructures whose coupled states can be monitored by means of microspectroscopy.
DOI
We demonstrate a pronounced color change in the light scattered from thermally fluctuating optically trapped octahedral gold nanoparticles (OGPs) in water using a tightly focused near-infrared laser beam. Monodispersed OGPs with an average edge length of 67 ± 6.5 nm were synthesized using a polyol method. Using dark-field microscopy, we observed successive changes of color (i.e., red → green → yellow) scattered from the trapped OGPs. We analyzed this trapping behavior by means of Rayleigh scattering microspectroscopy and concluded that pairs of OGPs trapped in the potential well interact with each other to form dimers oriented in the direction of the electric field vector of the trapping laser light. We theoretically obtained the absorption and scattering cross sections and the enhancement factors of the electric field of an OGP dimer in three different configurations by means of finite-difference time-domain calculations. The calculations suggest that the dimers become preferentially oriented in a vertex-to-vertex configuration because of the high polarizability. These findings indicate that optical tweezers are a promising technique for creating highly ordered assemblies of plasmonic nanostructures whose coupled states can be monitored by means of microspectroscopy.
DOI
Photothermal forces enhanced by nanoneedle array for nanoparticle manipulation Author links open overlay panel
Yufeng Li, Xudong Liu, Jing Li, J. Wu
Plasmonic nanostructures provide strong electromagnetic fields enhancement and confinement for nanoparticle trapping. Here, we study the thermal and optical nanoparticle trapping effects using plasmonic nanoneedles array. Results show that the photo-thermal force outside the nanostructure can affect movements of nanoparticles in the far field as a result of heat transfer. The thermal force is decreased about one order of magnitude for nanoparticle at about away from the nanostructure where the optical force is no longer effective. Plasmonic nanoneedles with high aspect ratio provides more trapping positions in three dimensions. The thermal force together with the near field optical force make plasmonic nanoneedles array a flexible and wide working range manipulation strategy for nanoparticles.
DOI
Plasmonic nanostructures provide strong electromagnetic fields enhancement and confinement for nanoparticle trapping. Here, we study the thermal and optical nanoparticle trapping effects using plasmonic nanoneedles array. Results show that the photo-thermal force outside the nanostructure can affect movements of nanoparticles in the far field as a result of heat transfer. The thermal force is decreased about one order of magnitude for nanoparticle at about away from the nanostructure where the optical force is no longer effective. Plasmonic nanoneedles with high aspect ratio provides more trapping positions in three dimensions. The thermal force together with the near field optical force make plasmonic nanoneedles array a flexible and wide working range manipulation strategy for nanoparticles.
DOI
Raman Tweezers for Small Microplastics and Nanoplastics Identification in Seawater
Raymond Gillibert, Gireeshkumar Balakrishnan, Quentin Deshoules, Morgan Tardivel, Alessandro Magazzù, Maria Grazia Donato, Onofrio M. Maragò, Marc Lamy de La Chapelle, Florent Colas, Fabienne Lagarde, Pietro G. Gucciardi
Our understanding of the fate and distribution of micro- and nano- plastics in the marine environment is limited by the intrinsic difficulties of the techniques currently used for the detection, quantification, and chemical identification of small particles in liquid (light scattering, vibrational spectroscopies, and optical and electron microscopies). Here we introduce Raman Tweezers (RTs), namely optical tweezers combined with Raman spectroscopy, as an analytical tool for the study of micro- and nanoplastics in seawater. We show optical trapping and chemical identification of sub-20 μm plastics, down to the 50 nm range. Analysis at the single particle level allows us to unambiguously discriminate plastics from organic matter and mineral sediments, overcoming the capacities of standard Raman spectroscopy in liquid, intrinsically limited to ensemble measurements. Being a microscopy technique, RTs also permits one to assess the size and shapes of particles (beads, fragments, and fibers), with spatial resolution only limited by diffraction. Applications are shown on both model particles and naturally aged environmental samples, made of common plastic pollutants, including polyethylene, polypropylene, nylon, and polystyrene, also in the presence of a thin eco-corona. Coupled to suitable extraction and concentration protocols, RTs have the potential to strongly impact future research on micro and nanoplastics environmental pollution, and enable the understanding of the fragmentation processes on a multiscale level of aged polymers.
DOI
Our understanding of the fate and distribution of micro- and nano- plastics in the marine environment is limited by the intrinsic difficulties of the techniques currently used for the detection, quantification, and chemical identification of small particles in liquid (light scattering, vibrational spectroscopies, and optical and electron microscopies). Here we introduce Raman Tweezers (RTs), namely optical tweezers combined with Raman spectroscopy, as an analytical tool for the study of micro- and nanoplastics in seawater. We show optical trapping and chemical identification of sub-20 μm plastics, down to the 50 nm range. Analysis at the single particle level allows us to unambiguously discriminate plastics from organic matter and mineral sediments, overcoming the capacities of standard Raman spectroscopy in liquid, intrinsically limited to ensemble measurements. Being a microscopy technique, RTs also permits one to assess the size and shapes of particles (beads, fragments, and fibers), with spatial resolution only limited by diffraction. Applications are shown on both model particles and naturally aged environmental samples, made of common plastic pollutants, including polyethylene, polypropylene, nylon, and polystyrene, also in the presence of a thin eco-corona. Coupled to suitable extraction and concentration protocols, RTs have the potential to strongly impact future research on micro and nanoplastics environmental pollution, and enable the understanding of the fragmentation processes on a multiscale level of aged polymers.
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Highly Sensitive Mass Detection Using Optically Levitated Microdisks
Jian Liu; Ka-Di Zhu
We propose a mass sensor using optically trapped and cooled dielectric microdisks. The center-of-mass motion of a trapped particle in vacuum can experience extremely low dissipation resulting in robust decoupling from the heat bath. It leads to a long heating time thus the measurement can be accomplished before a jump in the phonon number without the optomechanical cooling. This method can lead to milli-dalton mass sensitivity which approximates to the mass of one electron.
DOI
We propose a mass sensor using optically trapped and cooled dielectric microdisks. The center-of-mass motion of a trapped particle in vacuum can experience extremely low dissipation resulting in robust decoupling from the heat bath. It leads to a long heating time thus the measurement can be accomplished before a jump in the phonon number without the optomechanical cooling. This method can lead to milli-dalton mass sensitivity which approximates to the mass of one electron.
DOI
Work extraction, information-content and the Landauer bound in the continuous Maxwell Demon
M Ribezzi-Crivellari and F Ritort
In a recent paper we introduced a continuous version of the Maxwell demon (CMD) that is capable of extracting large amounts of work per cycle by repeated measurements of the state of the system Ribezzi-Crivellari and Ritort (2019 Nat. Phys.). Here we underline its main features such as the role played by the Landauer limit in the average extracted work, the continuous character of the measurement process and the differences between our continuous Maxwell demon and an autonomous Maxwell demon. We demonstrate the reversal of Landauer's inequality depending on the thermodynamical and mechanical stability of the work extracting substance. We also emphasize the robustness of the Shannon definition of the information-content of the stored sequences in the limit where work extraction is maximal and fueled by the large information-content of rare events.
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In a recent paper we introduced a continuous version of the Maxwell demon (CMD) that is capable of extracting large amounts of work per cycle by repeated measurements of the state of the system Ribezzi-Crivellari and Ritort (2019 Nat. Phys.). Here we underline its main features such as the role played by the Landauer limit in the average extracted work, the continuous character of the measurement process and the differences between our continuous Maxwell demon and an autonomous Maxwell demon. We demonstrate the reversal of Landauer's inequality depending on the thermodynamical and mechanical stability of the work extracting substance. We also emphasize the robustness of the Shannon definition of the information-content of the stored sequences in the limit where work extraction is maximal and fueled by the large information-content of rare events.
DOI
Wednesday, September 25, 2019
Assembly of Topographical Micropatterns with Optoelectronic Tweezers
Shuailong Zhang, Yifan Zhai, Ran Peng, Moein Shayegannia, Andrew G. Flood, Juntian Qu, Xinyu Liu, Nazir P. Kherani, Aaron R. Wheeler
Topographical micropatterns (TMPs), or ordered arrays of 3D features on a flat surface, have become important for a wide range of applications. A new optofluidic method based on optoelectronic tweezers to assemble TMPs from suspensions of microparticles in fluid is reported. After assembly, TMPs can be freeze‐dried and then transferred to alternate substrates. 3D simulations are carried out to clarify the experimental results and techniques are developed to evaluate pattern‐transfer fidelity, which is found to be >90% for a wide range of different structures. The optofluidic assembly method described here is facile and accessible, suggesting utility for a wide range of microfabrication and microassembly applications in the future.
DOI
Topographical micropatterns (TMPs), or ordered arrays of 3D features on a flat surface, have become important for a wide range of applications. A new optofluidic method based on optoelectronic tweezers to assemble TMPs from suspensions of microparticles in fluid is reported. After assembly, TMPs can be freeze‐dried and then transferred to alternate substrates. 3D simulations are carried out to clarify the experimental results and techniques are developed to evaluate pattern‐transfer fidelity, which is found to be >90% for a wide range of different structures. The optofluidic assembly method described here is facile and accessible, suggesting utility for a wide range of microfabrication and microassembly applications in the future.
DOI
Contactless optical trapping and manipulation of nanoparticles utilizing SIBA mechanism and EDL force
Mahdi Sahafi and Amir Habibzadeh-Sharif
On-chip optical tweezers based on evanescent fields overcome the diffraction limit of the free-space optical tweezers and can be a promising technique for developing lab-on-a-chip devices. While such trapping allows for low-cost and precise manipulation, it suffers from unavoidable contact with the device surface, which eliminates one of the major advantages of the optical trapping. Here, we use a 1D photonic crystal cavity to trap nanoparticles and propose a novel method to control and manipulate the particle distance from the cavity utilizing a self-induced back-action (SIBA) mechanism and electrical-double-layer (EDL) force. It is numerically shown that a 200 nm radius silica particle can be trapped near the cavity with a potential well deeper than 178kBT by 1 mW of input power without any contact with the surface and easily moved vertically with nanometer precision by wavelength detuning.
DOI
On-chip optical tweezers based on evanescent fields overcome the diffraction limit of the free-space optical tweezers and can be a promising technique for developing lab-on-a-chip devices. While such trapping allows for low-cost and precise manipulation, it suffers from unavoidable contact with the device surface, which eliminates one of the major advantages of the optical trapping. Here, we use a 1D photonic crystal cavity to trap nanoparticles and propose a novel method to control and manipulate the particle distance from the cavity utilizing a self-induced back-action (SIBA) mechanism and electrical-double-layer (EDL) force. It is numerically shown that a 200 nm radius silica particle can be trapped near the cavity with a potential well deeper than 178kBT by 1 mW of input power without any contact with the surface and easily moved vertically with nanometer precision by wavelength detuning.
DOI
Perspective on light-induced transport of particles: from optical forces to phoretic motion
Pavel Zemánek, Giorgio Volpe, Alexandr Jonáš, and Oto Brzobohatý
Propulsive effects of light, which often remain unnoticed in our daily-life experience, manifest themselves on spatial scales ranging from subatomic to astronomical. Light-mediated forces can indeed confine individual atoms, cooling their effective temperature very close to absolute zero, as well as contribute to cosmological phenomena such as the formation of stellar planetary systems. In this review, we focus on the transport processes that light can initiate on small spatial scales. In particular, we discuss in depth various light-induced mechanisms for the controlled transport of microscopic particles; these mechanisms rely on the direct transfer of momentum between the particles and the incident light waves, on the combination of optical forces with external forces of other nature, and on light-triggered phoretic motion. After a concise theoretical overview of the physical origins of optical forces, we describe how these forces can be harnessed to guide particles either in continuous bulk media or in the proximity of a constraining interface under various configurations of the illuminating light beams (radiative, evanescent, or plasmonic fields). Subsequently, we introduce particle transport techniques that complement optical forces with counteracting forces of non-optical nature. We finally discuss particle actuation schemes where light acts as a fine knob to trigger and/or modulate phoretic motion in spatial gradients of non-optical (e.g., electric, chemical, or temperature) fields. We conclude by outlining possible future fundamental and applied directions for research in light-induced particle transport. We believe that this comprehensive review can inspire diverse, interdisciplinary scientific communities to devise novel, unorthodox ways of assembling and manipulating materials with light.
DOI
Propulsive effects of light, which often remain unnoticed in our daily-life experience, manifest themselves on spatial scales ranging from subatomic to astronomical. Light-mediated forces can indeed confine individual atoms, cooling their effective temperature very close to absolute zero, as well as contribute to cosmological phenomena such as the formation of stellar planetary systems. In this review, we focus on the transport processes that light can initiate on small spatial scales. In particular, we discuss in depth various light-induced mechanisms for the controlled transport of microscopic particles; these mechanisms rely on the direct transfer of momentum between the particles and the incident light waves, on the combination of optical forces with external forces of other nature, and on light-triggered phoretic motion. After a concise theoretical overview of the physical origins of optical forces, we describe how these forces can be harnessed to guide particles either in continuous bulk media or in the proximity of a constraining interface under various configurations of the illuminating light beams (radiative, evanescent, or plasmonic fields). Subsequently, we introduce particle transport techniques that complement optical forces with counteracting forces of non-optical nature. We finally discuss particle actuation schemes where light acts as a fine knob to trigger and/or modulate phoretic motion in spatial gradients of non-optical (e.g., electric, chemical, or temperature) fields. We conclude by outlining possible future fundamental and applied directions for research in light-induced particle transport. We believe that this comprehensive review can inspire diverse, interdisciplinary scientific communities to devise novel, unorthodox ways of assembling and manipulating materials with light.
DOI
Approach to fully decomposing an optical force into conservative and nonconservative components
Xinning Yu, Yikun Jiang, Huajin Chen, Shiyang Liu, and Zhifang Lin
One of the theoretical challenges in studying optical trapping is the decomposition of the optical force into the gradient force (conservative component) and scattering force (nonconservative component), which can be achieved either for Raleigh particles or for very large particles in the regime of ray optics. However, for the moderate particles in between these two limits, the scenario is still a mystery. In this paper we present a theoretical approach to bridge this gap and fully split the optical force acting on a spherical particle immersed in a generic monochromatic free-space optical field into two such essentially different components, which is efficient even for large particles with the exact consideration of light polarization, thus offering a benchmark for examining the effective range for application of ray optics. Our approach models general optical fields by a series of homogeneous plane waves. The analytical expressions for the gradient and scattering parts of the optical force exerted on a spherical particle of arbitrary size illuminated by multiple interferential plane waves are then derived. As examples of applications, we investigate the gradient and scattering forces acting on a dielectric particle immersed in the Bessel beam. Our results are in excellent agreement with those obtained based on ray optics methods when the illuminated particle is large enough, while exhibiting effects of Mie resonance that are totally missing in the ray optics for moderate particle sizes. Finally, we study the effect of particle size on the gradient force acting on a spherical particle sitting in multiple interferential plane waves. Our extensively numerical results, up to a size as large as 2000 illuminating wavelengths, suggest an overall decreasing tendency in the ratio of the magnitude of the gradient force to that of the total force as the particle size increases.
DOI
One of the theoretical challenges in studying optical trapping is the decomposition of the optical force into the gradient force (conservative component) and scattering force (nonconservative component), which can be achieved either for Raleigh particles or for very large particles in the regime of ray optics. However, for the moderate particles in between these two limits, the scenario is still a mystery. In this paper we present a theoretical approach to bridge this gap and fully split the optical force acting on a spherical particle immersed in a generic monochromatic free-space optical field into two such essentially different components, which is efficient even for large particles with the exact consideration of light polarization, thus offering a benchmark for examining the effective range for application of ray optics. Our approach models general optical fields by a series of homogeneous plane waves. The analytical expressions for the gradient and scattering parts of the optical force exerted on a spherical particle of arbitrary size illuminated by multiple interferential plane waves are then derived. As examples of applications, we investigate the gradient and scattering forces acting on a dielectric particle immersed in the Bessel beam. Our results are in excellent agreement with those obtained based on ray optics methods when the illuminated particle is large enough, while exhibiting effects of Mie resonance that are totally missing in the ray optics for moderate particle sizes. Finally, we study the effect of particle size on the gradient force acting on a spherical particle sitting in multiple interferential plane waves. Our extensively numerical results, up to a size as large as 2000 illuminating wavelengths, suggest an overall decreasing tendency in the ratio of the magnitude of the gradient force to that of the total force as the particle size increases.
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Microparticle transport networks with holographic optical tweezers and cavitation bubbles
Pedro A. Quinto-Su
Optical transport networks for active absorbing microparticles are made with holographic optical tweezers. The particles are powered by the optical potentials that make the network and transport themselves via random vapor-propelled hops to different traps. The geometries explored for the optical traps are square lattices, circular arrays, and random arrays. The degree distribution for the connections or possible paths between the traps are localized like in the case of random networks. The average travel times across 𝑛 different traps scale as 𝑛𝑏 with exponents in the range of 2.06 and 2.31, in agreement with random walks on connected networks (upper bound ∝𝑛3). Finally, a particle traveling the network attracts others as a result of the vapor explosions enhancing transport.
DOI
Optical transport networks for active absorbing microparticles are made with holographic optical tweezers. The particles are powered by the optical potentials that make the network and transport themselves via random vapor-propelled hops to different traps. The geometries explored for the optical traps are square lattices, circular arrays, and random arrays. The degree distribution for the connections or possible paths between the traps are localized like in the case of random networks. The average travel times across 𝑛 different traps scale as 𝑛𝑏 with exponents in the range of 2.06 and 2.31, in agreement with random walks on connected networks (upper bound ∝𝑛3). Finally, a particle traveling the network attracts others as a result of the vapor explosions enhancing transport.
DOI
Induced radiation force of an optical line source on a cylinder material exhibiting circular dichroism
F. G. Mitri
The optical radiation force experienced by a cylinder material of circular cross section exhibiting circular dichroism (known also as rotary polarization) in an electric line source illumination is considered. An exact analytical expression for the radiation force (per length) valid for any frequency range is derived assuming an electric line source radiating cylindrically diverging TM-polarized waves without any approximations. The partial-wave series expansion method in cylindrical coordinates utilizing standard Bessel and Hankel functions is used to derive the electric and magnetic field expressions and a dimensionless radiation force function (or efficiency), which depends on the scattering coefficient of the cylinder as well as the distance from the radiating source. To illustrate the analysis, numerical computations for the dimensionless radiation force function for a perfect electromagnetic conductor (PEMC) cylinder are performed with emphasis on its dimensionless size parameter and source distance, which clearly draw attention to the contribution of the cross-polarized scattered waves (resulting from the rotary polarization effect) to the total force. The numerical predictions demonstrate the possibility to pull a circular-shaped cylinder material with rotary polarization toward the illuminating electric line source with TM-polarized waves using a curved wavefront depending on the PEMC material admittance, distance to the source, and size of the cylinder.
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Polarization effect on optical manipulation in a three-beam optical lattice
Guangji Ha, Hongxia Zheng, Xinning Yu, and Zhifang Lin
We study the effect of polarization on optical micromanipulation in a hexagonal optical lattice formed by three equiamplitude plane waves that have their wave vectors lying equiangularly in a plane, taking into account the vectorial characteristic of the electromagnetic waves. It is demonstrated that different polarizations generate different optical force landscapes, resulting in a trapping versus detrapping phenomenon tunable by tailoring the polarization of the incident beams. The physical origin of the polarization effect on the force landscapes is then traced to the ratio between the conservative (gradient) and nonconservative (scattering) optical forces acting on a particle immersed in the three-wave optical lattice. The trapping-detrapping transition phenomenon due to the change of polarization in small particles, where the gradient force dominates, is revealed to originate from the reverse of the conservative optical force, which manifests itself by a transition of the optical potential energy landscape from one exhibiting a periodic distribution of pits to one showing a distribution of humps over space. Our results suggest an alternative handle to manipulate small particle by tuning the polarization.
DOI
We study the effect of polarization on optical micromanipulation in a hexagonal optical lattice formed by three equiamplitude plane waves that have their wave vectors lying equiangularly in a plane, taking into account the vectorial characteristic of the electromagnetic waves. It is demonstrated that different polarizations generate different optical force landscapes, resulting in a trapping versus detrapping phenomenon tunable by tailoring the polarization of the incident beams. The physical origin of the polarization effect on the force landscapes is then traced to the ratio between the conservative (gradient) and nonconservative (scattering) optical forces acting on a particle immersed in the three-wave optical lattice. The trapping-detrapping transition phenomenon due to the change of polarization in small particles, where the gradient force dominates, is revealed to originate from the reverse of the conservative optical force, which manifests itself by a transition of the optical potential energy landscape from one exhibiting a periodic distribution of pits to one showing a distribution of humps over space. Our results suggest an alternative handle to manipulate small particle by tuning the polarization.
DOI
Funnel beams in the defocusing nonlinear media
Yuanqiang Peng, Xiaolin Wu, Yunqi Li and Weiyi Hong
The dynamics of the inward-focusing ring Airy beam in the defocusing nonlinear media is investigated. It is found an interesting phenomenon that the propagation of the inward-focusing ring Airy beam exhibits a "funnel" when the beam intensity is sufficiently high. Additionally, the focus spot of such a funnel beam monotonously changes with the nonlocality of the media. The gradient force of the funnel beam is also studied in detail. The findings may pave the way to the optical tweezers in the nonlinear regime.
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The dynamics of the inward-focusing ring Airy beam in the defocusing nonlinear media is investigated. It is found an interesting phenomenon that the propagation of the inward-focusing ring Airy beam exhibits a "funnel" when the beam intensity is sufficiently high. Additionally, the focus spot of such a funnel beam monotonously changes with the nonlocality of the media. The gradient force of the funnel beam is also studied in detail. The findings may pave the way to the optical tweezers in the nonlinear regime.
DOI
Monday, September 23, 2019
Above and beyond: holographic tracking of axial displacements in holographic optical tweezers
Michael J. O’Brien and David G. Grier
How far a particle moves along the optical axis in a holographic optical trap is not simply dictated by the programmed motion of the trap, but rather depends on an interplay of the trap’s changing shape and the particle’s material properties. For the particular case of colloidal spheres in optical tweezers, holographic video microscopy reveals that trapped particles tend to move farther along the axial direction than the traps that are moving them and that different kinds of particles move by different amounts. These surprising and sizeable variations in axial placement can be explained by a dipole-order theory for optical forces. Their discovery highlights the need for real-time feedback to achieve precise control of colloidal assemblies in three dimensions and demonstrates that holographic microscopy can meet that need.
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How far a particle moves along the optical axis in a holographic optical trap is not simply dictated by the programmed motion of the trap, but rather depends on an interplay of the trap’s changing shape and the particle’s material properties. For the particular case of colloidal spheres in optical tweezers, holographic video microscopy reveals that trapped particles tend to move farther along the axial direction than the traps that are moving them and that different kinds of particles move by different amounts. These surprising and sizeable variations in axial placement can be explained by a dipole-order theory for optical forces. Their discovery highlights the need for real-time feedback to achieve precise control of colloidal assemblies in three dimensions and demonstrates that holographic microscopy can meet that need.
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Efficient Prediction and Analysis of Optical Trapping at Nanoscale via Finite Element Tearing and Interconnecting Method
Ting Wan, Benliu Tang
Numerical simulation plays an important role for the prediction of optical trapping based on plasmonic nano-optical tweezers. However, complicated structures and drastic local field enhancement of plasmonic effects bring great challenges to traditional numerical methods. In this article, an accurate and efficient numerical simulation method based on a dual-primal finite element tearing and interconnecting (FETI-DP) and Maxwell stress tensor is proposed, to calculate the optical force and potential for trapping nanoparticles. A low-rank sparsification approach is introduced to further improve the FETI-DP simulation performance. The proposed method can decompose a large-scale and complex problem into small-scale and simple problems by using non-overlapping domain division and flexible mesh discretization, which exhibits high efficiency and parallelizability. Numerical results show the effectiveness of the proposed method for the prediction and analysis of optical trapping at nanoscale.
DOI
Numerical simulation plays an important role for the prediction of optical trapping based on plasmonic nano-optical tweezers. However, complicated structures and drastic local field enhancement of plasmonic effects bring great challenges to traditional numerical methods. In this article, an accurate and efficient numerical simulation method based on a dual-primal finite element tearing and interconnecting (FETI-DP) and Maxwell stress tensor is proposed, to calculate the optical force and potential for trapping nanoparticles. A low-rank sparsification approach is introduced to further improve the FETI-DP simulation performance. The proposed method can decompose a large-scale and complex problem into small-scale and simple problems by using non-overlapping domain division and flexible mesh discretization, which exhibits high efficiency and parallelizability. Numerical results show the effectiveness of the proposed method for the prediction and analysis of optical trapping at nanoscale.
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Casimir–Lifshitz Force Based Optical Resonators
Victoria Esteso, Sol Carretero-Palacios, Hernán Míguez
We theoretically investigate the building of optical resonators based on the levitation properties of thin films subjected to strong repulsive Casimir–Lifshitz forces when immersed in an adequate medium and confronted with a planar substrate. We propose a design in which cavities supporting high Q-factor optical modes at visible frequencies can be achieved by means of combining commonly found materials, such as silicon oxide, polystyrene or gold, with glycerol as a mediating medium. We use the balance between flotation and repulsive Casimir–Lifshitz forces in the system to accurately tune the optical cavity thickness and hence its modes. The effects of other forces, such as electrostatic, that may come into play are also considered. Our results constitute a proof of concept that may open the route to the design of photonic architectures in environments in which dispersion forces play a substantial role and could be of particular relevance for devising novel microfluidic optical resonators.
DOI
We theoretically investigate the building of optical resonators based on the levitation properties of thin films subjected to strong repulsive Casimir–Lifshitz forces when immersed in an adequate medium and confronted with a planar substrate. We propose a design in which cavities supporting high Q-factor optical modes at visible frequencies can be achieved by means of combining commonly found materials, such as silicon oxide, polystyrene or gold, with glycerol as a mediating medium. We use the balance between flotation and repulsive Casimir–Lifshitz forces in the system to accurately tune the optical cavity thickness and hence its modes. The effects of other forces, such as electrostatic, that may come into play are also considered. Our results constitute a proof of concept that may open the route to the design of photonic architectures in environments in which dispersion forces play a substantial role and could be of particular relevance for devising novel microfluidic optical resonators.
DOI
Realization of a high power optical trapping setup free from thermal lensing effects
C. Simonelli, E. Neri, A. Ciamei, I. Goti, M. Inguscio, A. Trenkwalder, and M. Zaccanti
Transmission of high power laser beams through partially absorbing materials modifies the light propagation via a thermally-induced effect known as thermal lensing. This may cause changes in the beam waist position and degrade the beam quality. Here we characterize the effect of thermal lensing associated with the different elements typically employed in an optical trapping setup for cold atoms experiments. We find that the only relevant thermal lens is represented by the TeO2 crystal of the acousto-optic modulator exploited to adjust the laser power on the atomic sample. We then devise a simple and totally passive scheme that enables to realize an inexpensive optical trapping apparatus essentially free from thermal lensing effects.
DOI
Transmission of high power laser beams through partially absorbing materials modifies the light propagation via a thermally-induced effect known as thermal lensing. This may cause changes in the beam waist position and degrade the beam quality. Here we characterize the effect of thermal lensing associated with the different elements typically employed in an optical trapping setup for cold atoms experiments. We find that the only relevant thermal lens is represented by the TeO2 crystal of the acousto-optic modulator exploited to adjust the laser power on the atomic sample. We then devise a simple and totally passive scheme that enables to realize an inexpensive optical trapping apparatus essentially free from thermal lensing effects.
DOI
Calculation of optical forces for arbitrary light beams using the Fourier ray method
Meng Shao, Shuhe Zhang, Jinhua Zhou, and Yu-Xuan Ren
The ray-optics (RO) model is a reasonable method to calculate optical force in geometrical optics regime. However, the RO model fails to calculate the optical force produced by diffractive optical field and other arbitrary structured light beams. We propose the Fourier ray (FR) method to calculate the optical force for arbitrary incident beams. Combining the Fourier optics and the geometrical optics, the FRs are defined as rays that inlay on the plane waves weighted by the Fourier angular spectrum of the incident beam. According to traditional RO model and FR method, we can analyze optical forces on a microsphere immersed in various beams. To validate the FR method, forces of the fundamental Gaussian beam and Airy beam are respectively calculated and compared with traditional method. In addition, optical forces in three arbitrary structured light beams are demonstrated as well. Our simulations show that the FR method is able to evaluate the optical forces generated by diffractive optical field and complex structured light beams, and give a solid prediction of their trapping performances. In RO regime, the Fourier ray method is a universal method to predict the interaction between bead and complex optical field.
DOI
The ray-optics (RO) model is a reasonable method to calculate optical force in geometrical optics regime. However, the RO model fails to calculate the optical force produced by diffractive optical field and other arbitrary structured light beams. We propose the Fourier ray (FR) method to calculate the optical force for arbitrary incident beams. Combining the Fourier optics and the geometrical optics, the FRs are defined as rays that inlay on the plane waves weighted by the Fourier angular spectrum of the incident beam. According to traditional RO model and FR method, we can analyze optical forces on a microsphere immersed in various beams. To validate the FR method, forces of the fundamental Gaussian beam and Airy beam are respectively calculated and compared with traditional method. In addition, optical forces in three arbitrary structured light beams are demonstrated as well. Our simulations show that the FR method is able to evaluate the optical forces generated by diffractive optical field and complex structured light beams, and give a solid prediction of their trapping performances. In RO regime, the Fourier ray method is a universal method to predict the interaction between bead and complex optical field.
DOI
Radiation forces on a Rayleigh particle produced by partially coherent circular Airy beams
Mingli Sun, Jiahao Zhang, Nan Li, Kaikai Huang, Huizhu Hu, Xian Zhang, and Xuanhui Lu
In this work, the radiation force on a Rayleigh dielectric particle induced by the partially coherent circular Airy beam (PCCAB) is investigated. Our numerical results show that the PCCAB can be used to trap and manipulate particles. The radiation force distribution and trapping stability have been analyzed under different coherent lengths. It is found that, with the increase of the spatial coherent length, the radiation force is increased and the particle can be stably trapped at more points. Therefore, the radiation force as well as the depth of potential well can be effectively modulated by controlling the spatial coherent length in optical micromanipulation. The trapping properties of PCCAB have also been studied under other different parameters, including the scale factor and initial radius.
DOI
In this work, the radiation force on a Rayleigh dielectric particle induced by the partially coherent circular Airy beam (PCCAB) is investigated. Our numerical results show that the PCCAB can be used to trap and manipulate particles. The radiation force distribution and trapping stability have been analyzed under different coherent lengths. It is found that, with the increase of the spatial coherent length, the radiation force is increased and the particle can be stably trapped at more points. Therefore, the radiation force as well as the depth of potential well can be effectively modulated by controlling the spatial coherent length in optical micromanipulation. The trapping properties of PCCAB have also been studied under other different parameters, including the scale factor and initial radius.
DOI
Circular Dichroism in Rotating Particles
Deng Pan, Hongxing Xu, and F. Javier García de Abajo
Light interaction with rotating nanostructures gives rise to phenemona as varied as optical torques and quantum friction. Surprisingly, the most basic optical response function of nanostructures undergoing rotation has not been clearly addressed so far. Here we reveal that mechanical rotation results in circular dichroism in optically isotropic particles, which show an unexpectedly strong dependence on the particle internal geometry. More precisely, particles with one-dimensionally confined electron motion in the plane perpendicular to the rotation axis, such as nanorings and nanocrosses, exhibit a splitting of 2Ω in the particle optical resonances, while compact particles, such as nanodisks and nanospheres, display weak circular dichroism. We base our findings on a quantum-mechanical description of the polarizability of rotating particles, incorporating the mechanical rotation by populating the particle electronic states according to the principle that they are thermally equilibrated in the rotating frame. We further provide insight into the rotational superradience effect and the ensuing optical gain, originating in population inversion as regarded from the lab frame, in which the particle is out of equilibrium. Surprisingly, we find the optical frequency cutoff for superradiance to deviate from the rotation frequency Ω. Our results unveil a rich, unexplored phenomenology of light interaction with rotating objects, which might find applications in various fields, such as optical trapping and sensing.
DOI
Light interaction with rotating nanostructures gives rise to phenemona as varied as optical torques and quantum friction. Surprisingly, the most basic optical response function of nanostructures undergoing rotation has not been clearly addressed so far. Here we reveal that mechanical rotation results in circular dichroism in optically isotropic particles, which show an unexpectedly strong dependence on the particle internal geometry. More precisely, particles with one-dimensionally confined electron motion in the plane perpendicular to the rotation axis, such as nanorings and nanocrosses, exhibit a splitting of 2Ω in the particle optical resonances, while compact particles, such as nanodisks and nanospheres, display weak circular dichroism. We base our findings on a quantum-mechanical description of the polarizability of rotating particles, incorporating the mechanical rotation by populating the particle electronic states according to the principle that they are thermally equilibrated in the rotating frame. We further provide insight into the rotational superradience effect and the ensuing optical gain, originating in population inversion as regarded from the lab frame, in which the particle is out of equilibrium. Surprisingly, we find the optical frequency cutoff for superradiance to deviate from the rotation frequency Ω. Our results unveil a rich, unexplored phenomenology of light interaction with rotating objects, which might find applications in various fields, such as optical trapping and sensing.
DOI
Observation of a symmetry-protected topological phase of interacting bosons with Rydberg atoms
Sylvain de Léséleuc, Vincent Lienhard, Pascal Scholl, Daniel Barredo, Sebastian Weber, Nicolai Lang, Hans Peter Büchler, Thierry Lahaye, Antoine Browaeys
The concept of topological phases is a powerful framework for characterizing ground states of quantum many-body systems that goes beyond the paradigm of symmetry breaking. Topological phases can appear in condensed-matter systems naturally, whereas the implementation and study of such quantum many-body ground states in artificial matter require careful engineering. Here, we report the experimental realization of a symmetry-protected topological phase of interacting bosons in a one-dimensional lattice and demonstrate a robust ground state degeneracy attributed to protected zero-energy edge states. The experimental setup is based on atoms trapped in an array of optical tweezers and excited into Rydberg levels, which gives rise to hard-core bosons with an effective hopping generated by dipolar exchange interaction.
DOI
The concept of topological phases is a powerful framework for characterizing ground states of quantum many-body systems that goes beyond the paradigm of symmetry breaking. Topological phases can appear in condensed-matter systems naturally, whereas the implementation and study of such quantum many-body ground states in artificial matter require careful engineering. Here, we report the experimental realization of a symmetry-protected topological phase of interacting bosons in a one-dimensional lattice and demonstrate a robust ground state degeneracy attributed to protected zero-energy edge states. The experimental setup is based on atoms trapped in an array of optical tweezers and excited into Rydberg levels, which gives rise to hard-core bosons with an effective hopping generated by dipolar exchange interaction.
DOI
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