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Vincent Loke

The University of Queensland, Australia, School of Mathematics and Physics, Adjunct

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The University of Queensland, Australia

Arkansas State University

Manuel Nieto-Vesperinas

CSIC (Consejo Superior de Investigaciones Científicas-Spanish National Research Council)

Christian Brousseau

University of St Andrews

stefano pagliara

University of Exeter

Antonio Alvaro Ranha Neves

UFABC - Federal University of ABC

Mohammad Al-Othmani

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Papers by Vincent Loke

Engineering Optically Driven Micromachines

Proceedings of Spie the International Society For Optical Engineering, Aug 28, 2008

Optical forces and torques acting on microscopic objects trapped in focussed laser beams promise ... more Optical forces and torques acting on microscopic objects trapped in focussed laser beams promise flexible methods of driving micromachines through a microscope cover slip or even a cell wall. We are endeavouring to engineer special purpose micro-objects for a range of tasks. Colloidal self assembly of calcium carbonate provides birefringent spheres which can exert considerable torque, while two photon polymerisation allows us to fabricate objects of arbitrary shape that can be designed to exchange both spin and orbital angular momentum. Numerical calculations of forces and torques can allow an optimal design, and optical measurements provide us with certain knowledge of the forces and torques which are actually exerted.

Toolbox for Calculation of Optical Forces and Torques

Piers 2007 Beijing Progress in Electromagnetics Research Symposium Pts I and Ii Proceedings, 2007

We describe a toolbox, implemented in Matlab, for the computational modelling of optical forces a... more

Computational modeling of optical trapping of vaterite microspheres

The ability to grow microscopic spherical birefringent crystals of vaterite, a calcium carbonate ... more

Optical vortex trapping and the dynamics of particle rotation

Since the pioneering work by He and colleagues [34,35], the transport of optical angular momentum... more Since the pioneering work by He and colleagues [34,35], the transport of optical angular momentum by optical vortex beams has been applied to the rotation of microscopic particles in optical traps. Even earlier, optical vortex traps had been proposed as a method to reduce the scattering forces that oppose optical trapping; in the ray optics picture, only high-angle rays contribute to the gradient force, and the use of a hollow beam eliminates the low-angle rays that would still contribute to the scattering force [1].

Modelling optical micro-machines

A strongly focused laser beam can be used to trap, manipulate and exert torque on a microparticle... more A strongly focused laser beam can be used to trap, manipulate and exert torque on a microparticle. The torque is the result of transfer of angular momentum by scattering of the laser beam. The laser could be used to drive a rotor, impeller, cog wheel or some other microdevice of a few microns in size, perhaps fabricated from a birefringent material. We review our methods of computationally simulating the torque and force imparted by a laser beam. We introduce a method of hybridizing the T-matrix with the Finite Difference Frequency Domain (FDFD) method to allow the modelling of materials that are anisotropic and inhomogeneous, and structures that have complex shapes. The high degree of symmetry of a microrotor, such as discrete or continuous rotational symmetry, can be exploited to reduce computational time and memory requirements by orders of magnitude. This is achieved by performing calculations for only a given segment or plane that is repeated across the whole structure. This ca...

DDA with Surface Interaction: Computational Toolbox for MATLAB

Journal of Quantitative Spectroscopy and Radiative Transfer

We describe a MATLAB toolbox that utilizes the discrete-dipole approximation (DDA) method for mod... more We describe a MATLAB toolbox that utilizes the discrete-dipole approximation (DDA) method for modelling light interaction with arbitrarily-shape scatterers in free space as well with planar surface interaction (DDA-SI). The range of applicable models range from optical micromanipulation, plamonics, nano-antennae, near-field coupling and general light interaction with scatterers ranging from a few nanometers to several microns in size.

Interaction of nanoparticles on a substrate with an AFM probe: DDA-SI formulation

Motivated by the need for a modeling tool for nanostructures interacting with a substrate and an ... more Motivated by the need for a modeling tool for nanostructures interacting with a substrate and an AFM probe, we developed a MATLAB implementation of the discrete dipole approximation with surface interactions (DDA-SI). The method is applied to investigate the near-field coupling between particles on the surface and an AFM probe. The results presented here explore the effects of a number of physical, geometrical and material properties that can eventually assist nanolithography, particularly in defining the parameters for nano-writing.

Tailoring Particles for Optical Trapping and Micromanipulation: An Overview

PIERS Online, 2008

Optical trapping and micromanipulation has developed from an interesting novelty to a powerful an... more Optical trapping and micromanipulation has developed from an interesting novelty to a powerful and widely used tool, with the capability to move or trap microscopic live biological specimens and measure forces on the order of piconewtons, typical of forces in microbiological systems. Despite this, the range of particles typically trapped or manipulated is quite small, and it is unusual to see applications involving objects other than biological specimens or homogeneous isotropic microspheres, typically polymer or silica. However, particles can be modified or specially fabricated to expand the possible applications of optical tweezers. For example, while non-absorbing homogeneous isotropic spheres cannot be rotated, optically anisotropic spheres can, and can therefore function as microscopic torque sensors, extending the usual translational micromanipulation and force measurement to rotational manipulation and torque sensing. The development of such particles has led to applications in microscale metrology and biophysics, along with potential deployment of optically-driven micromachines in lab-on-a-chip devices. We present an overview of our work on the tailoring of microparticles for versatile optical trapping and micromanipulation. This includes approaches based on controlled chemistry -nanoassembly -and optical microfabrication. Beginning with the production of anisotropic vaterite microspheres, we review some of the applications, and difficulties encountered along the way. Some of these difficulties can be overcome by coating of the vaterite microspheres. We also discuss the use of anti-reflection coating to allow strong trapping of high refractive index particles. The alternative strategy of producing arbitrarily shaped polymer microstructures through two-photon photopolymerization is also discussed. This can be used to produce optically-driven microrotors or structurally anisotropic microspheres to replace vaterites for particular applications.

Optical Vortex Trapping and the Dynamics of Particle Rotation

Structured Light and Its Applications, 2008

Since the pioneering work by He and colleagues [34,35], the transport of optical angular momentum... more Since the pioneering work by He and colleagues [34,35], the transport of optical angular momentum by optical vortex beams has been applied to the rotation of microscopic particles in optical traps. Even earlier, optical vortex traps had been proposed as a method to reduce the scattering forces that oppose optical trapping; in the ray optics picture, only high-angle rays contribute to the gradient force, and the use of a hollow beam eliminates the low-angle rays that would still contribute to the scattering force [1].

Driving Optical Micromachines with Orbital Angular Momentum

Applications of Light with Orbital Angular Momentum, 2011

Design of Optically Driven Microrotors

Optical Nano and Micro Actuator Technology, 2012

Theory and Practice of Computational Modeling and Simulation of Optical Tweezers

Optics in the Life Sciences, 2015

Comparison of T-matrix calculation methods for scattering by cylinders in optical tweezers

Optics letters, Jan 15, 2014

The T-matrix method, or the T-matrix formulation of scattering, is a framework for mathematically... more The T-matrix method, or the T-matrix formulation of scattering, is a framework for mathematically describing the scattering properties of an object as a linear relationship between expansion coefficients of the incident and scattering fields in a basis of vector spherical wave functions (VSWFs). A variety of methods can be used to calculate the T-matrix. We explore the applicability of the extended boundary condition method (EBCM) and point matching (PM) method to calculate the T-matrix for scattering by cylinders in optical tweezers and hence the optical force acting on them. We compare both methods with the discrete-dipole approximation (DDA) to measure their accuracy for different sizes and aspect ratios (ARs) for Rayleigh and wavelength-size cylinders. We determine range of sizes and ARs giving errors below 1% and 10%. These results can help researchers choose the most efficient method to calculate the T-matrix for nonspherical particles with acceptable accuracy.

Driving corrugated donut rotors with Laguerre-Gauss beams

Optics express, Jan 11, 2014

Tightly-focused laser beams that carry angular momentum have been used to trap and rotate microro... more Tightly-focused laser beams that carry angular momentum have been used to trap and rotate microrotors. In particular, a Laguerre-Gauss mode laser beam can be used to transfer its orbital angular momentum to drive microrotors. We increase the torque efficiency by a factor of about 2 by designing the rotor such that its geometry is compatible with the driving beam, when driving the rotation with the optimum beam, rather than beams of higher or lower orbital angular momentum. Based on Floquet's theorem, the order of discrete rotational symmetry of the rotor can be made to couple with the azimuthal mode of the Laguerre-Gauss beam. We design corrugated donut rotors, that have a flat disc-like profile, with the help of the discrete dipole approximation and the T-matrix methods in parallel with experimental demonstrations of stable trapping and torque measurement. We produce and test such a rotor using two-photon photopolymerization. With a rotor that has 8-fold discrete rotational sym...

Surface waves and atomic force microscope probe-particle near-field coupling: discrete dipole approximation with surface interaction

Journal of the Optical Society of America. A, Optics, image science, and vision, 2010

Evanescent waves on a surface form due to the collective motion of charges within the medium. The... more Evanescent waves on a surface form due to the collective motion of charges within the medium. They do not carry any energy away from the surface and decay exponentially as a function of the distance. However, if there is any object within the evanescent field, electromagnetic energy within the medium is tunneled away and either absorbed or scattered. In this case, the absorption is localized, and potentially it can be used for selective diagnosis or nanopatterning applications. On the other hand, scattering of evanescent waves can be employed for characterization of nanoscale structures and particles on the surface. In this paper we present a numerical methodology to study the physics of such absorption and scattering mechanisms. We developed a MATLAB implementation of discrete dipole approximation with surface interaction (DDA-SI) in combination with evanescent wave illumination to investigate the near-field coupling between particles on the surface and a probe. This method can be ...

Can Optically Driven Micromachines be Useful in Biomedicine? Optical Tweezers at Work

Asia Optical Fiber Communication and Optoelectronic Exposition and Conference, 2008

ABSTRACT

<title>Engineering optically driven micromachines</title>

Optical Trapping and Optical Micromanipulation V, 2008

Optical forces and torques acting on microscopic objects trapped in focussed laser beams promise ... more Optical forces and torques acting on microscopic objects trapped in focussed laser beams promise flexible methods of driving micromachines through a microscope cover slip or even a cell wall. We are endeavouring to engineer special purpose micro-objects for a range of tasks. Colloidal self assembly of calcium carbonate provides birefringent spheres which can exert considerable torque, while two photon polymerisation allows us to fabricate objects of arbitrary shape that can be designed to exchange both spin and orbital angular momentum. Numerical calculations of forces and torques can allow an optimal design, and optical measurements provide us with certain knowledge of the forces and torques which are actually exerted.

<title>Optically driven micromachines: progress and prospects</title>

Photonics: Design, Technology, and Packaging II, 2005

The ability to exert optical torques to rotationally manipulate microparticles has developed from... more The ability to exert optical torques to rotationally manipulate microparticles has developed from an interesting curiosity to seeing deployment in practical applications. Is the next step to genuine optically-driven micromachines feasible or possible? We review the progress made towards this goal, and future prospects.

Towards Efficient Modelling of Optical Micromanipulation of Complex Structures

Computational methods for electromagnetic and light scattering can be used for the calculation of... more Computational methods for electromagnetic and light scattering can be used for the calculation of optical forces and torques. Since typical particles that are optically trapped or manipulated are on the order of the wavelength in size, approximate methods such as geometric optics or Rayleigh scattering are inapplicable, and solution or either the Maxwell equations or the vector Helmholtz equation must be resorted to. Traditionally, such solutions were only feasible for the simplest geometries; modern computational power enable the rapid solution of more general-but still simple-geometries such as axisymmetric, homogeneous, and isotropic scatterers. However, optically-driven micromachines necessarily require more complex geometries, and their computational modelling thus remains in the realm of challenging computational problems. We review our progress towards efficient computational modelling of optical tweezers and micromanipulation, including the trapping and manipulation of complex structures such as optical micromachines. In particular, we consider the exploitation of symmetry in the modelling of such devices.

Toolbox for Calculation of Optical Forces and Torques

We describe a toolbox, implemented in Matlab, for the computational modelling of optical forces a... more

Engineering Optically Driven Micromachines

Proceedings of Spie the International Society For Optical Engineering, Aug 28, 2008

Optical forces and torques acting on microscopic objects trapped in focussed laser beams promise ... more Optical forces and torques acting on microscopic objects trapped in focussed laser beams promise flexible methods of driving micromachines through a microscope cover slip or even a cell wall. We are endeavouring to engineer special purpose micro-objects for a range of tasks. Colloidal self assembly of calcium carbonate provides birefringent spheres which can exert considerable torque, while two photon polymerisation allows us to fabricate objects of arbitrary shape that can be designed to exchange both spin and orbital angular momentum. Numerical calculations of forces and torques can allow an optimal design, and optical measurements provide us with certain knowledge of the forces and torques which are actually exerted.

Toolbox for Calculation of Optical Forces and Torques

Piers 2007 Beijing Progress in Electromagnetics Research Symposium Pts I and Ii Proceedings, 2007

We describe a toolbox, implemented in Matlab, for the computational modelling of optical forces a... more

Computational modeling of optical trapping of vaterite microspheres

The ability to grow microscopic spherical birefringent crystals of vaterite, a calcium carbonate ... more

Optical vortex trapping and the dynamics of particle rotation

Since the pioneering work by He and colleagues [34,35], the transport of optical angular momentum... more Since the pioneering work by He and colleagues [34,35], the transport of optical angular momentum by optical vortex beams has been applied to the rotation of microscopic particles in optical traps. Even earlier, optical vortex traps had been proposed as a method to reduce the scattering forces that oppose optical trapping; in the ray optics picture, only high-angle rays contribute to the gradient force, and the use of a hollow beam eliminates the low-angle rays that would still contribute to the scattering force [1].

Modelling optical micro-machines

A strongly focused laser beam can be used to trap, manipulate and exert torque on a microparticle... more A strongly focused laser beam can be used to trap, manipulate and exert torque on a microparticle. The torque is the result of transfer of angular momentum by scattering of the laser beam. The laser could be used to drive a rotor, impeller, cog wheel or some other microdevice of a few microns in size, perhaps fabricated from a birefringent material. We review our methods of computationally simulating the torque and force imparted by a laser beam. We introduce a method of hybridizing the T-matrix with the Finite Difference Frequency Domain (FDFD) method to allow the modelling of materials that are anisotropic and inhomogeneous, and structures that have complex shapes. The high degree of symmetry of a microrotor, such as discrete or continuous rotational symmetry, can be exploited to reduce computational time and memory requirements by orders of magnitude. This is achieved by performing calculations for only a given segment or plane that is repeated across the whole structure. This ca...

DDA with Surface Interaction: Computational Toolbox for MATLAB

Journal of Quantitative Spectroscopy and Radiative Transfer

We describe a MATLAB toolbox that utilizes the discrete-dipole approximation (DDA) method for mod... more We describe a MATLAB toolbox that utilizes the discrete-dipole approximation (DDA) method for modelling light interaction with arbitrarily-shape scatterers in free space as well with planar surface interaction (DDA-SI). The range of applicable models range from optical micromanipulation, plamonics, nano-antennae, near-field coupling and general light interaction with scatterers ranging from a few nanometers to several microns in size.

Interaction of nanoparticles on a substrate with an AFM probe: DDA-SI formulation

Motivated by the need for a modeling tool for nanostructures interacting with a substrate and an ... more Motivated by the need for a modeling tool for nanostructures interacting with a substrate and an AFM probe, we developed a MATLAB implementation of the discrete dipole approximation with surface interactions (DDA-SI). The method is applied to investigate the near-field coupling between particles on the surface and an AFM probe. The results presented here explore the effects of a number of physical, geometrical and material properties that can eventually assist nanolithography, particularly in defining the parameters for nano-writing.

Tailoring Particles for Optical Trapping and Micromanipulation: An Overview

PIERS Online, 2008

Optical trapping and micromanipulation has developed from an interesting novelty to a powerful an... more Optical trapping and micromanipulation has developed from an interesting novelty to a powerful and widely used tool, with the capability to move or trap microscopic live biological specimens and measure forces on the order of piconewtons, typical of forces in microbiological systems. Despite this, the range of particles typically trapped or manipulated is quite small, and it is unusual to see applications involving objects other than biological specimens or homogeneous isotropic microspheres, typically polymer or silica. However, particles can be modified or specially fabricated to expand the possible applications of optical tweezers. For example, while non-absorbing homogeneous isotropic spheres cannot be rotated, optically anisotropic spheres can, and can therefore function as microscopic torque sensors, extending the usual translational micromanipulation and force measurement to rotational manipulation and torque sensing. The development of such particles has led to applications in microscale metrology and biophysics, along with potential deployment of optically-driven micromachines in lab-on-a-chip devices. We present an overview of our work on the tailoring of microparticles for versatile optical trapping and micromanipulation. This includes approaches based on controlled chemistry -nanoassembly -and optical microfabrication. Beginning with the production of anisotropic vaterite microspheres, we review some of the applications, and difficulties encountered along the way. Some of these difficulties can be overcome by coating of the vaterite microspheres. We also discuss the use of anti-reflection coating to allow strong trapping of high refractive index particles. The alternative strategy of producing arbitrarily shaped polymer microstructures through two-photon photopolymerization is also discussed. This can be used to produce optically-driven microrotors or structurally anisotropic microspheres to replace vaterites for particular applications.

Optical Vortex Trapping and the Dynamics of Particle Rotation

Structured Light and Its Applications, 2008

Since the pioneering work by He and colleagues [34,35], the transport of optical angular momentum... more Since the pioneering work by He and colleagues [34,35], the transport of optical angular momentum by optical vortex beams has been applied to the rotation of microscopic particles in optical traps. Even earlier, optical vortex traps had been proposed as a method to reduce the scattering forces that oppose optical trapping; in the ray optics picture, only high-angle rays contribute to the gradient force, and the use of a hollow beam eliminates the low-angle rays that would still contribute to the scattering force [1].

Driving Optical Micromachines with Orbital Angular Momentum

Applications of Light with Orbital Angular Momentum, 2011

Design of Optically Driven Microrotors

Optical Nano and Micro Actuator Technology, 2012

Theory and Practice of Computational Modeling and Simulation of Optical Tweezers

Optics in the Life Sciences, 2015

Comparison of T-matrix calculation methods for scattering by cylinders in optical tweezers

Optics letters, Jan 15, 2014

The T-matrix method, or the T-matrix formulation of scattering, is a framework for mathematically... more The T-matrix method, or the T-matrix formulation of scattering, is a framework for mathematically describing the scattering properties of an object as a linear relationship between expansion coefficients of the incident and scattering fields in a basis of vector spherical wave functions (VSWFs). A variety of methods can be used to calculate the T-matrix. We explore the applicability of the extended boundary condition method (EBCM) and point matching (PM) method to calculate the T-matrix for scattering by cylinders in optical tweezers and hence the optical force acting on them. We compare both methods with the discrete-dipole approximation (DDA) to measure their accuracy for different sizes and aspect ratios (ARs) for Rayleigh and wavelength-size cylinders. We determine range of sizes and ARs giving errors below 1% and 10%. These results can help researchers choose the most efficient method to calculate the T-matrix for nonspherical particles with acceptable accuracy.

Driving corrugated donut rotors with Laguerre-Gauss beams

Optics express, Jan 11, 2014

Tightly-focused laser beams that carry angular momentum have been used to trap and rotate microro... more Tightly-focused laser beams that carry angular momentum have been used to trap and rotate microrotors. In particular, a Laguerre-Gauss mode laser beam can be used to transfer its orbital angular momentum to drive microrotors. We increase the torque efficiency by a factor of about 2 by designing the rotor such that its geometry is compatible with the driving beam, when driving the rotation with the optimum beam, rather than beams of higher or lower orbital angular momentum. Based on Floquet's theorem, the order of discrete rotational symmetry of the rotor can be made to couple with the azimuthal mode of the Laguerre-Gauss beam. We design corrugated donut rotors, that have a flat disc-like profile, with the help of the discrete dipole approximation and the T-matrix methods in parallel with experimental demonstrations of stable trapping and torque measurement. We produce and test such a rotor using two-photon photopolymerization. With a rotor that has 8-fold discrete rotational sym...

Surface waves and atomic force microscope probe-particle near-field coupling: discrete dipole approximation with surface interaction

Journal of the Optical Society of America. A, Optics, image science, and vision, 2010

Evanescent waves on a surface form due to the collective motion of charges within the medium. The... more Evanescent waves on a surface form due to the collective motion of charges within the medium. They do not carry any energy away from the surface and decay exponentially as a function of the distance. However, if there is any object within the evanescent field, electromagnetic energy within the medium is tunneled away and either absorbed or scattered. In this case, the absorption is localized, and potentially it can be used for selective diagnosis or nanopatterning applications. On the other hand, scattering of evanescent waves can be employed for characterization of nanoscale structures and particles on the surface. In this paper we present a numerical methodology to study the physics of such absorption and scattering mechanisms. We developed a MATLAB implementation of discrete dipole approximation with surface interaction (DDA-SI) in combination with evanescent wave illumination to investigate the near-field coupling between particles on the surface and a probe. This method can be ...

Can Optically Driven Micromachines be Useful in Biomedicine? Optical Tweezers at Work

Asia Optical Fiber Communication and Optoelectronic Exposition and Conference, 2008

ABSTRACT

<title>Engineering optically driven micromachines</title>

Optical Trapping and Optical Micromanipulation V, 2008

Optical forces and torques acting on microscopic objects trapped in focussed laser beams promise ... more Optical forces and torques acting on microscopic objects trapped in focussed laser beams promise flexible methods of driving micromachines through a microscope cover slip or even a cell wall. We are endeavouring to engineer special purpose micro-objects for a range of tasks. Colloidal self assembly of calcium carbonate provides birefringent spheres which can exert considerable torque, while two photon polymerisation allows us to fabricate objects of arbitrary shape that can be designed to exchange both spin and orbital angular momentum. Numerical calculations of forces and torques can allow an optimal design, and optical measurements provide us with certain knowledge of the forces and torques which are actually exerted.

<title>Optically driven micromachines: progress and prospects</title>

Photonics: Design, Technology, and Packaging II, 2005

The ability to exert optical torques to rotationally manipulate microparticles has developed from... more The ability to exert optical torques to rotationally manipulate microparticles has developed from an interesting curiosity to seeing deployment in practical applications. Is the next step to genuine optically-driven micromachines feasible or possible? We review the progress made towards this goal, and future prospects.

Towards Efficient Modelling of Optical Micromanipulation of Complex Structures

Computational methods for electromagnetic and light scattering can be used for the calculation of... more Computational methods for electromagnetic and light scattering can be used for the calculation of optical forces and torques. Since typical particles that are optically trapped or manipulated are on the order of the wavelength in size, approximate methods such as geometric optics or Rayleigh scattering are inapplicable, and solution or either the Maxwell equations or the vector Helmholtz equation must be resorted to. Traditionally, such solutions were only feasible for the simplest geometries; modern computational power enable the rapid solution of more general-but still simple-geometries such as axisymmetric, homogeneous, and isotropic scatterers. However, optically-driven micromachines necessarily require more complex geometries, and their computational modelling thus remains in the realm of challenging computational problems. We review our progress towards efficient computational modelling of optical tweezers and micromanipulation, including the trapping and manipulation of complex structures such as optical micromachines. In particular, we consider the exploitation of symmetry in the modelling of such devices.

Toolbox for Calculation of Optical Forces and Torques

We describe a toolbox, implemented in Matlab, for the computational modelling of optical forces a... more