A dual-beam method for the near-axial rotation of dielectric nanorods was devised. The method uses two laser beams, where a focused Gaussian beam holds the object in the beam axis while a focused Laguerre-Gaussian beam rotates the object. The near-axial rotation of ZnO nanorods using this method was then experimentally demonstrated, and the radial offset distance of the rotating nanorod from the beam axis was quantified via a video tracking method.
Three-dimensional position of optically trapped dielectric particles can be detected by measuring the back-focal plane
interference pattern of incident and scattered fields. Time-domain surface current based near zone to far zone
transformation was implemented to compute the interference pattern by a spherical scatterer under a focused Gaussian beam. Computed results are compared with experimental data for validations.
Microassembly has been identified as one of critical techniques in innovating the promising era of micro/nano
technology. Several works have been investigated to fabricate various micro-devices such as micro-sensors and microactuators.
Assembly plays an important role for fabricating micro-devices. However, there are only few studies in the
assembly of microparts. In this paper, we present manipulation and assembly of three-dimensional microparts produced
by two-photon polymerization where optical trapping technique was used to manipulate microparts. We show exemplary
microassembly formed by assembling two microparts, a movable female part and a male part fixed on a glass substrate.
Optical trapping of nanorods has attracted many researchers due to many potential applications of nanorods in sensor
technologies. It is well known that nanorods align with the propagation axis or the polarization direction of a laser beam.
However, there are only few studies about the axial rotation of nanorods. In this study, we present a method for the
measurement of the rotational frequency of nanorods.
This paper reports the measurement of elastic constants between two DNA strands that are simultaneously hybridized by
a third target-DNA linker. Two probe-DNA strands that are immobilized on fluorescent beads and a target-DNA linker
formed a hybridized assembly through the Watson-Crick based pairing. Elastic constants of the resulting assembly were
measured using a force calibrated dual optical trap. This study can be used to detect the existence of a target-DNA linker
with a specified nucleotide sequence, indicating its potential use in DNA biosensors.
We investigate that components held in multiple optical traps can be manipulated and assembled together using snap-fit assembly. There are several works on manipulating microscopic objects with optical tweezers and assembling them. However, these techniques cannot sustain the assembled structure after turning off the laser source. In contrast, our technique utilizes snap-fit assembly so that assembled components do not detach. With this approach, components and sub-assemblies can be readily controlled in real-time and assembled into a permanent assembly. Our method can be used for constructing micrometer scale devices.
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 design of a microscopy system tailored for optical tweezers with a capability of an automatic focusing is presented. In this design, we utilize lenses, motorized mechanical stage, lamp and a digital camera to magnify and see a micrometer sized spheres floating in a thin film of water. The system can automatically translate the stage that holds the specimen to obtain the best focused image. The best focused image is "sharp." Mathematically, the best focused image shows the maximum amount of high frequency terms from the images obtained by translating the stage. The metric that calculates how one image is focused is called the Focus Measure (FM). Unfortunately, low frequency components also increase this FM. And an optical imaging system is a low pass filtering system. Thus the primary concern is to lower the low frequency components in an image. The electric signals from each pixel of a CCD include noises that are inherent in each pixel. The result of this is an FM profile that has multiple local maxima. This is the most critical reason why an Automatic Focusing System (AFS) yields incorrect focusing results. Available techniques have been tested and from this experience, the most appropriate Focus Measure Filter (FMF) that has the sharpest FM despite the low frequency terms and noises has been selected. Furthermore, a maximum search algorithm that is immune to local maxima in an FM profile is discussed. Using this FMF and search algorithm, an Automatic focusing system (AFS) tailored for optical tweezers is presented. The system is implemented on personal computers equipped with Pentium 4 processors.
There are increased needs for manipulating microscopic objects. One of enabling technologies is an instrument called optical tweezers (OT) that uses a focused laser beam to trap and move microscopic objects. OT has been shown effective for directly manipulating spherical, cylindrical or axis-symmetrical shapes. For other forms of shapes that do not show any symmetry, there have been works on using micrometer sized balls as a handle to indirectly manipulate the objects. Direct manipulation is difficult because complex trapping potential needs to be calculated to stably trap non-symmetrical shapes. User interfaces for these "indirect" systems use a computer mouse to design a layout of balls for surrounding (holding) an object and a trajectory that describes how these balls as a whole moves. The contained object pushed by these surrounding balls then moves accordingly. In this study, we introduce an intuitive user interface system for manipulating these balls. Using virtual reality gloves, each finger tip position of an operator is used to position control these balls. This user interface system enables the operator to intuitively grasp, move and release irregular formed shapes.
Optical tweezers (OT) uses a focused laser beam to trap and move microscopic objects. The design of OT consists of laying out stationary and moving (or rotating) lenses and mirrors so that two design constraints are met at the objective back aperture (OBA): 1) the laser beam has to be pivoted around the center, and 2) the beam has to keep the same degree of overfilling. While these constraints are met, the objectives are to maximize the divergence/convergence angle and the beam rotation angle at the OBA. They are each accomplished by moving a lens or rotating a mirror, respectively. There are few known designs that give (claimed) good performances while satisfying above constraints. However, these designs are improvised inventions with no attempts in optimization. In this paper, we propose a new method for designing an optimized OT that achieves the best performance with given pool of optical elements. Our method, (Topology Optimization of the Optical Tweezers Setup) first divides the layout space into finite lattices and then distributes lenses and mirrors to appropriate lattices. Subsequently, whether the attempted configuration conforms to the constraints is tested. If the test is successful, the layout and its performance are recorded. At the end, the best performing layout is found. In this paper, we primarily concentrate on optimizing the positions of lens components. In the future, this approach will be generalized for more complicated configurations that include mirror components.