Thomas W. LeBrun

Algorithms for On-Line Monitoring of Micro Spheres in an Optical Tweezers-Based Assembly Cell

Optical tweezers have emerged as a powerful tool for micro and nanomanipulation. Using optical tweezers to perform automated assembly requires on-line monitoring of components in the assembly workspace. This paper presents algorithms for estimating positions and orientations of microscale and nanoscale components in the 3-Dimensional assembly workspace. Algorithms presented in this paper use images obtained by optical section microscopy. The images are first segmented to locate areas of interest and then image gradient information from the areas of interest is used to generate probable locations and orientations of components in the XY-plane. Finally, signature curves are computed and utilized to obtain component locations and orientations in 3-D space. We have tested these algorithms with silica micro-spheres as well as metallic nanowires. We believe that the algorithms described in this paper will provide the foundation for realizing automated assembly operations in optical tweezers-based assembly cells.Copyright

A six-degree-of-freedom precision motion stage

This article presents the design and performance evaluation of a six-degree-of-freedom piezoelectrically actuated fine motion stage that will be used for three dimensional error compensation of a long-range translation mechanism. Development of a single element, piezoelectric linear displacement actuator capable of translations of 1.67 μm with 900 V potential across the electrodes and under a 27.4 N axial load and 0.5 mm lateral distortion is presented. Finite element methods have been developed and used to evaluate resonant frequencies of the stage platform and the complete assembly with and without a platform payload. In general, an error of approximately 10.0% between the finite element results and the experimentally measured values were observed. The complete fine motion stage provided approximately ±0.93 μm of translation and ±38.0 μrad of rotation in all three planes of motion using an excitation range of 1000 V. An impulse response indicating a fundamental mode resonance at 162 Hz was measured with...

Generating Simplified Trapping Probability Models From Simulation of Optical Tweezers System

This paper presents a radial basis function based approach to generate simplified models to estimate the trapping probability in optical trapping experiments using offline simulations. The difference form of Langevins equation is used to perform physically accurate simulations of a particle under the influence of a trapping potential and is used to estimate trapping probabilities at discrete points in the parameter space. Gaussian radial basis functions combined with kd-tree based partitioning of the parameter space are then used to generate simplified models of trapping probability. We show that the proposed approach is computationally efficient in estimating the trapping probability and that the estimated probability using the simplified models is sufficiently close to the probability estimates from offline simulation data.

A Flexible System Framework for a Nanoassembly Cell Using Optical Tweezers

The optical tweezers instrument is a unique tool for directed assembly of nanocomponents. In order to function as a viable nanomanufacturing tool, a software architecture is needed to run the optical tweezers hardware, provide an effective user interface, and allow automated operation. A flexible software system framework is described to utilize the optical tweezers hardware to its full potential. Initially we lay out the requirements for the system framework and define the broad architectural choices made while implementing the different modules. Implementation details of key system modules are then described. The flexible nature of the architecture is demonstrated by showing how a simulation module can be seamlessly included into the framework to replace the optical tweezers hardware as necessary. Finally, we show some representative assembly operations to demonstrate the capabilities of the system.Copyright

Significantly improved trapping lifetime of nanoparticles in an optical trap using feedback control.

We demonstrate an increase in trapping lifetime for optically trapped nanoparticles by more than an order of magnitude using feedback control, with no corresponding increase in beam power. Langevin dynamics simulations were used to design the control law, and this technique was then demonstrated experimentally using 100 nm gold particles and 350 nm silica particles. No particle escapes were detected with the controller on, leading to lower limits on the increase in lifetime for 100 nm gold particles of 26 times (at constant average beam power) and 22 times for 350 nm silica particles (with average beam power reduced by one-third). The approach described here can be combined with other techniques, such as counter propagating beams or higher-order optical modes, to trap the smallest nanoparticles and can be used to reduce optical heating of particles that are susceptible to photodamage, such as biological systems.

Stochastic Simulations With Graphics Hardware: Characterization of Accuracy and Performance

Methods to implement stochastic simulations on the graphics processing unit (GPU) have been developed. These algorithms are used in a simulation of microassembly and nanoassembly with optical tweezers, but are also directly compatible with simulations of a wide variety of assembly techniques using either electrophoretic, magnetic, or other trapping techniques. Significant speedup is possible for stochastic particle simulations when using the GPU, included in most personal computers (PCs), rather than the central processing unit (CPU) that handles most calculations. However, a careful analysis of the accuracy and precision when using the GPU in stochastic simulations is lacking and is addressed here. A stochastic simulation for spherical particles has been developed and mapped onto stages of the GPU hardware that provide the best performance. The results from the CPU and GPU implementation are then compared with each other and with well-established theory. The error in the mean ensemble energy and the diffusion constant is measured for both the CPU and the GPU implementations. The time taken to complete several simulation experiments on each platform has also been measured and the speedup attained by the GPU is then calculated.

Algorithms for On-Line Monitoring of Components in an Optical Tweezers-Based Assembly Cell

Optical tweezers have emerged as a powerful tool for micro and nanomanipulation. Using optical tweezers to perform automated assembly requires on-line monitoring of components in the assembly workspace. This paper presents algorithms for estimating positions and orientations of microscale and nanoscale components in the 3-Dimensional assembly workspace. Algorithms presented in this paper use images obtained by optical section microscopy. The images are first segmented to locate areas of interest and then image gradient information from the areas of interest is used to generate probable locations and orientations of components in the XY-plane. Finally, signature curves are computed and utilized to obtain component locations and orientations in 3-D space. We have tested these algorithms with silica micro-spheres as well as metallic nanowires. We believe that the algorithms described in this paper will provide the foundation for realizing automated assembly operations in optical tweezers-based assembly cells.Copyright

Three-Dimensional Scanning Optical Tweezers

There are several new tools for manipulating microscopic objects. Among them, optical tweezers (OT) has two distinguishing advantages. Firstly, OT can easily release an object without the need of a complicated detaching scheme. Secondly, it is anticipated to manipulate an object with six degrees of freedom. OT is realized by tightly focusing a laser beam on microscopic objects. Grabbing and releasing is easily done by turning a laser beam on and off. For doing a dexterous manipulation on an object, a complicated potential trap must be calculated and applied. We foresee that such calculation method will be developed in the near future. One of the candidates for implementing the calculated trap is scanning optical tweezers (SOT). SOT can be built by using actuators with a scanning frequency in the order of a hundred Hertz. We need fast scanners to stably trap an object. In this study, we present our design of such SOT. The SOT uses piezo-actuated tilt mirror and objective positioner to scan full three-dimensional workspace.

A modular system architecture for agile assembly of nanocomponents using optical tweezers

In order to realize the flexibility optical trapping offers as a nanoassembly tool, we need to develop natural and intuitive interfaces to assemble large quantities of nanocomponents quickly and cheaply. We propose a system to create such an interface that is scalable, inter-changeable and modular. Several prototypes are described, starting with simple interfaces that control a single trap in the optical tweezers instrument using a 3-dimensional Phantom haptic device. A networkbased approach is adopted early on, and a modular prototype is then described in detail. In such a design, individual modules developed on different platforms work independently and communicate with each other through a common language interface using the Neutral Messaging Language (NML) communication protocol. A natural user interface is implemented that can be used to create and manipulate traps interactively like in a CAD program. Modules such as image processing and automatic assembly are also added to help simplify routine assembly tasks. Drawing on lessons learned from the prototypes, a new system specification is formulated to better integrate the modules. Finally, conclusions are drawn on the overall viability and future of network-based systems for nanoassembly using optical tweezers.

Micro-mirror array control of optical tweezer trapping beams

The lack of tools to manipulate nanoscale objects is a major obstacle to fabricating and testing nanodevices. Optical tweezers are a promising tool for nanomanufacturing, but the efficiency of optical tweezer manufacturing depends on the number of trapping beams available. Micro optics technology offers the opportunity to significantly increase the number of trapping beams without a significant increase of the cost or size of the optics. Here we report on the sensors, optical circuit and the experimental work to control an array of laser beams generated by a single laser diode, for optical-tweezer-based nanomanufacturing. Our array of laser beams is generated by an array of servo controlled scanning dual-axis micro-mirrors. Capacitor electrodes underneath the micro-mirror plates provide electrostatic actuation, which allows control of the micro-mirror position. With proper reflecting surfaces it is possible to control the impact angle of the individual laser beams onto the micro-nano-particles, thus generating an optical beam gripper effect.