Robert C. Gauthier

Automated single-cell sorting system based on optical trapping

We provide a basis for automated single-cell sorting based on optical trapping and manipulation using human peripheral blood as a model system. A counterpropagating dual-beam optical-trapping configuration is shown theoretically and experimentally to be preferred due to a greater ability to manipulate cells in three dimensions. Theoretical analysis performed by simulating the propagation of rays through the region containing an erythrocyte (red blood cell) divided into numerous elements confirms experimental results showing that a trapped erythrocyte orients with its longest axis in the direction of propagation of the beam. The single-cell sorting system includes an image-processing system using thresholding, background subtraction, and edge-enhancement algorithms, which allows for the identification of single cells. Erythrocytes have been identified and manipulated into designated volumes using the automated dual-beam trap. Potential applications of automated single-cell sorting, including the incorporation of molecular biology techniques, are discussed.

Optical levitation of spheres: analytical development and numerical computations of the force equations

The force that is produced from the momentum change of a stream of photons incident upon micrometer-sized spheres is developed from a ray-optic model. The resulting force component expressions, axial and radial with respect to the photon stream center and incident direction, are in a form that makes them suitable for computer modeling of the levitation phenomena. Simulated results presented are in excellent agreement with published experimental observations.

Analysis of the behaviour of erythrocytes in an optical trapping system.

We present a theoretical analysis of the behaviour of erythrocytes in an optical trapping system. We modeled erythrocyte behaviour in an optical trap by an algorithm which divided the cell surface into a large number of elements and recursively summed the force and torque on each element. We present a relationship between the torque and angle of orientation of the cell, showing that stable equilibrium orientations are at angles of 0 o , 180 o and 360 o and unstable equilibrium orientations are at 90 o and 270 o relative to the axis of beam propagation. This is consistent with our experimental observations and with results described in the literature. We also model behaviour of the erythrocyte during micromanipulation by calculating the net force on it. Such theoretical analysis is practical as it allows for the optimization of the optical parameters of a trapping system prior to performing a specific optical micromanipulation application, such as cell sorting or construction of a cell pattern for lab-on-a-chip applications.

Nonlinear guided waves coupled nonlinearly in a planar GaAs/GaAlAs multiple quantum well structure

A nonlinear guided‐wave concept and nonlinear coupled‐wave equations are used to study numerically the coupling characteristics of two planar waveguides in a GaAs/GaAlAs multiple quantum well structure with self‐defocusing nonlinearities. Both the mode‐intensity‐dependent critical power and the coupling length are calculated for the first time using the nonlinear field distributions. An optically controlled modulation/switching behavior is predicted.

EXPERIMENTAL CONFIRMATION OF THE OPTICAL-TRAPPING PROPERTIES OF CYLINDRICAL OBJECTS

A sophisticated modeling program was used recently to predict the trapping and the manipulation properties of elongated cylindrical objects in the focal region of a high-intensity laser beam. On the basis of the model, the cylinders should align their longest diagonal dimension with the propagation axis of the laser beam and follow the beam when it is displaced transverse to the cylinders central axis. Experimental confirmation of the cylinders behavior is presented and confirms the suitability of the enhanced ray-optics approach to modeling micrometer-scale objects in optical-trap environments.

Computation of the optical trapping force using an FDTD based technique

The computation details related to computing the optical radiation pressure force on various objects using a 2-D grid FDTD algorithm are presented. The technique is based on propagating the electric and magnetic fields through the grid and determining the changes in the optical energy flow with and without the trap object(s) in the system. Traces displayed indicate that the optical forces and FDTD predicted object behavior are in agreement with published experiments and also determined through other computation techniques. We show computation results for a high and low dielectric disc and thin walled shell. The FDTD technique for computing the light-particle force interaction may be employed in all regimes relating particle dimensions to source wavelength. The algorithm presented here can be easily extended to 3-D and include torque computation algorithms, thus providing a highly flexible and universally useable computation engine.

Ray optics model and numerical computations for the radiation pressure micromotor

In this letter, the spinning of a micron sized radiation pressure motor is analyzed using geometrical optics to model for interactions of a highly focused laser beam with the medium discontinuities. The motor’s direction of rotation and dependence on focused beam parameters, predicted from the computations, are in agreement with previously published experimental results. The motor can be made to rotate in the clockwise or counterclockwise direction by changing the ambient medium only.

Theoretical and experimental considerations for a single-mode fiber-optic bend-type sensor

A novel single-mode bend fiber-optic sensing principle is presented. The design makes use of the translucent protective sheath that encases a typical fiber as a means of locating the position of a small bend present on an otherwise straight fiber. We can simultaneously determine bend magnitude by measuring the reduction in the fibers core light. The theoretical model presented and the experimental results obtained are in excellent agreement, suggesting that a single-point sensor system is feasible with the proposed technique.

Optical selection, manipulation, trapping, and activation of a microgear structure for applications in micro-optical-electromechanical systems.

The optical processes involved in laser trapping and optical manipulation are explored theoretically and experimentally as a means of activating a micrometer-size gear structure. We modeled the structure by using an enhanced ray-optics technique, and results indicate that the torque present on the gear can induce the gear to rotate about the gear-arm plane center with light as the driving energy source. We confirmed these findings experimentally by using gears manufactured with conventional semiconductor techniques and from a layer of polyimide. It is expected that such a simple gear design activated by use of light could lead to an entire new class of micro-optical-electromechanical systems.

Production of quasi-crystal template patterns using a dual beam multiple exposure technique

We present a dual beam multiple exposure technique that can generate complex 2-D quasi-crystal template structures. The optical system is based on the interference of two laser beams producing a family of high intensity planes. Controlled reorientation of a photosensitive sample between exposures results in an exposure dose, when developed, returns a quasi-crystal pattern. Results are shown in which quasi-crystal patterns with 8, 10, and 12-fold rotation symmetry are produced in photoresist. The results of several test runs are shown in which the quasi-crystal patterns developed in photoresist are subsequently etched into silicon. Based on an extended application of the dual beam multiple exposure optical system, a potential technique for producing 3-D quasi-crystal patterns is presented.