Particle Position Detection Research Articles

Gravitationally induced entanglement in a harmonic trap

Recent work has shown that it may be possible to detect gravitationally induced entanglement in tabletop experiments in the not-too-distant future. However, there are at present no thoroughly developed models for this type of experiment where the entangled particles are treated more fundamentally as excitations of a relativistic quantum field, and with the measurements modeled using expectation values of field observables. Here we propose a thought experiment where two particles are initially prepared in a superposition of coherent states within a common three-dimensional (3D) harmonic trap. The particles then develop entanglement through their mutual gravitational interaction, which can be probed through particle position detection probabilities. The present work gives a nonrelativistic quantum mechanical analysis of the gravitationally induced entanglement of this system, which we term the ``gravitational harmonium'' due to its similarity to the harmonium model of approximate electron interactions in a helium atom; the entanglement is operationally determined through the matter wave interference visibility. The present work serves as the basis for a subsequent investigation, which models this system using quantum field theory, providing further insights into the quantum nature of gravitationally induced entanglement through relativistic corrections, together with an operational procedure to quantify the entanglement.

Digital holographic particle position detection using two views and aperture reduction techniques

Digital holography is a well-established technique for tracer particle studies in a flow. Unfortunately, its great depth of focus increases the uncertainty along the Z axis. This drawback becomes very significant when the concentration of seeding particles increases. This is the case in real installations such as wind or water channel flows. In such cases, observing the whole volume, and therefore all the particles, and tracking individual particles in order to determine their motions becomes an awesome task. Getting a hologram of the whole scene is impossible with the existing photographic sensors. The solution offered by the present day technologies and academic studies is to take several holograms and synthesize the whole scene hologram. However, for getting individual particle behavior, it is necessary to make several processing steps, makes processing very complicated if the number of seeding tracer particles is relatively high, on one hand and on the other hand, the correlation between dynamic characteristics could not highly established. In such cases, the technique of one hologram is highly recommended. In order to overcome these problems, we propose here a new technique based on combining the two instantaneous orthogonal views and hologram aperture reduction (opposed to aperture synthesis). To establish the technique, we investigate a little volume with a reduced number of particles, and the development and experimental results are presented. We focus on the development and experimental application of this technique.

Reliable and mobile all-fiber modular optical tweezers

Miniaturization and integration of optical tweezers are attractive. Optical fiber-based trapping systems allow optical traps to be realized in miniature systems, but the optical traps in these systems lack reliability or mobility. Here, we present the all-fiber modular optical tweezers (AFMOTs), in which an optical trap can be reliably created and freely moved on a sample substrate. Two inclined optical fibers are permanently fixed to a common board, rendering a modular system where fiber alignments are maintained over months. The freely movable optical trap allows particles to be trapped in their native locations. As a demonstration, we applied AFMOTs to trap and deform freely floating individual cells. By the cell mechanical responses, we differentiated the nontumorigenic breast epithelial cell line (MCF10A) from its cancerous PTEN mutants (MCF10 PTEN-/-). To further expand the functionalities, three modalities of AFMOTs are demonstrated by changing the types of fibers for both the optical trap creation and particle position detection. As a miniature and modular system that creates a reliable and mobile optical trap, AFMOTs can find potential applications ranging from point-of-care diagnostics to education, as well as helping transition the optical trapping technology from the research lab to the field.

Detection of particle position from a linear interferometric out-of-focus image

A high precision method based on erosion match is proposed to extract the location coordinate of particles from a compression interferogram. With this method, particles can be positioned exactly when the overlap coefficients for that perpendicular and parallel to the fringes are less than 94.23% and 25% respectively. Super performance with the method is well confirmed by the synthetic and experiment data. Furthermore, the method can also be employed in the center detecting of complex fringe patterns for both circular and linear fringe images. The numerical and experimental results suggest that the method presented may be of considerable value to high-density spray field in accurately measuring both the particle location and its velocity.

光阱中微粒位置高精度检测技术

Precision sensing and measuring based on optical trap technology is innovation and deepening for application of optical force effect from micro-precise manipulation to precise measurement of physical quantities. Precision measurement of position information of the particle in optical trap is key technology of precise sensing and measuring. The method was put forward, which used digital image processing and curve fitting algorithm to detect particle positions in optical trap. The normalized self-correlation function of particle positions was obtained by digital image correlation, and the quadratic curve fitting was used to the normalized self-correlation function curve by least-square method to realize particle position detection of sub-pixel accuracy. Experiments show that the method described in this paper can effectively suppress the quantization effect of hardware and realize fast and high-precision detection of particle position in optical traps. Compared with the direct correlation method, the detection accuracy can be improved by at least one order of magnitude to 0.03 pixel.

Gradient in the electric field for particle position detection in microfluidic channels

In this work, a new method to track particles in microfluidic channels is presented. Particle position tracking in microfluidic systems is crucial to characterize sorting systems or to improve the analysis of cells in impedance flow cytometry studies. By developing an electric field gradient in a two parallel electrode array the position of the particles can be tracked in one axis by impedance analysis. This method can track the particle's position at lower frequencies and measure the conductivity of the system at higher frequencies. A 3-D simulation was performed showing particle position detection and conductivity analysis. To experimentally validate the technique, a microfluidic chip that develops a gradient in the electric field was fabricated and used to detect the position of polystyrene particles in one axis and measure their conductivity at low and high frequencies, respectively.

Adaptation of reference volumes for correlation-based digital holographic particle tracking

Numerically reconstructed reference volumes tailored to particle images are used for particle position detection by means of three-dimensional correlation. After a first tracking of these positions, the experimentally recorded particle images are retrieved as a posteriori knowledge about the particle images in the system. This knowledge is used for a further refinement of the detected positions. A transparent description of the individual algorithm steps including the results retrieved with experimental data complete the paper. The work employs extraordinarily small particles, smaller than the pixel pitch of the camera sensor. It is the first approach known to the authors that combines numerical knowledge about particle images and particle images retrieved from the experimental system to an iterative particle tracking approach for digital holographic particle tracking velocimetry.

A versatile major axis voted method for efficient ellipse detection

The recent developments in the field of particle science and technology show that the shape of the particle other than size and surface chemistry are important. Most commonly, digital images captured either by microscopy or other means are analyzed by image processing methods to completely characterize the shape of the objects. Among many possible shapes, ellipse like objects are ubiquitous and encountered across several disciplines - for example - face recognition in computer vision, classification of food grains and leaves, study of particle shape effects in colloid science, etc. Detection of particle position and their orientation is therefore of great interest to quantitatively understand the phenomena under investigation. In this article we propose a major axis voted method for the detection of ellipse-like objects in 2D images which is based on the assumption that each pair of boundary pixels are on the endpoints of the minor axis of the ellipse. We show that the method thus developed is capable of detecting occluded ellipses as well as deformed ellipses.

Effects of particle locations on reconstructed particle images in digital holography.

The intensity and phase reconstructed from digital in-line holograms by the convolution approach are analyzed. Distortions of particle images depending on their position in the plane transverse to the optical axis are identified. For this purpose, the object fields of numerically simulated particle holograms as well as of experimental data are reconstructed. The results of three-dimensional correlations of numerical and experimental data are superior when the numerically generated reference volumes are adapted to the transverse locations of the particle. Thus, proof is given that the characteristics of a particle image change distinctly with the transverse position of the particle and that the numerical model successfully simulates these changes. Hence, this knowledge can be integrated in future particle position detection algorithms.

Particle depth position detection by 2D correlation in digital in-line holography.

In digital holographic particle image velocimetry, hologram truncation is a very prominent problem when the projection of the particle position to the sensor is close to the sensor edge. Using the convolution approach to reconstruct such a hologram yields a deformed particle image compared to a particle image resulting from a particle with a projection to the center of the sensor. This Letter shows that the deformation complicates particle position detection based on an algorithm originally developed for analog holography by Choo and Kang, and later applied to digital holography by Yang and Kang. This algorithm is refined for the detection of particle positions from the deformed images and applied to numerical and experimental data.

Simultaneous calibration of optical tweezers spring constant and position detector response

We demonstrate a fast and direct calibration method for systems using a single laser for optical tweezers and particle position detection. The method takes direct advantage of back-focal-plane interferometry measuring not an absolute but a differential position, i.e. the position of the trapped particle relative to the center of the optical tweezers. Therefore, a fast step-wise motion of the optical tweezers yields the impulse response of the trapped particle. Calibration parameters such as the detector's spatial and temporal response and the spring constant of the optical tweezers then follow readily from fitting the measured impulse response.

Calibration of Holographic Optical Tweezers for Force Measurements on Biomaterials

Optical tweezers have been widely applied in the field of single-molecule biophysics, as the picoNewton forces that can be exerted and measured with this noninvasive technique lie in the force range of many biomolecular properties and events. By using trapped micrometer-sized particles as handles, the force-extension relations of macromolecules such as DNA and proteins have been probed. When probing more complex systems, however, such as cells or protein networks, the 3D character of these materials requires more flexibility in manipulating particles. With holographic optical tweezers, multiple optical traps can be manipulated independently in three dimensions in real time, adding this necessary flexibility to the interactive control over multiple particles. Thus far, however, holographic tweezers have not been an accepted tool in the biophysics community, in large part due to lack of evidence as to how exerted forces vary as the positions of holographic traps are changed. To perform quantitative force measurements, parameters such as trap stiffness and its position dependence, range of trap steering, and minimum step size are of key importance. Here, we systematically characterize the stiffness of traps within our holographic tweezers setup, in which high-speed (>kHz) camera imaging is used for particle position detection. We create multiple traps and steer one or more over small and large distances, and find that over a range of ∼25 μm the trap stiffness does not change significantly. Also, we determine the efficiency with which the laser power is directed towards intended traps. In addition, we control and detect trap displacements to ∼1 nm, comparable to the position detection limit of our system. Our results suggest that after full characterization, holographic optical tweezers can be successfully employed in quantitative experiments on biomaterials, e.g., probing elastomeric properties of structural protein networks.

Optical sorting and detection of submicrometer objects in a motional standing wave

An extended interference pattern close to surface may result in both a transmissive or evanescent surface fields for large area manipulation of trapped particles. The affinity of differing particle sizes to a moving standing wave light pattern allows us to hold and deliver them in a bi-directional manner and importantly demonstrate experimentally particle sorting in the sub-micron region. This is performed without the need of fluid flow (static sorting). Theoretical calculations experimentally confirm that certain sizes of colloidal particles thermally hop more easily between neighboring traps. A new generic method is also presented for particle position detection in an extended periodic light pattern and applied to characterization of optical traps and particle behavior

G904 Depth-from-defocusによる粒子分布検出法の測定精度(G.S.9 流れの計測技術2)

G904 Depth-from-defocusによる粒子分布検出法の測定精度(G.S.9 流れの計測技術2)

Construction of an ellipsoidal mirror analyzer for ion detection

An ellipsoidal mirror analyzer (EMA) has been constructed at the National Bureau of Standards for the analysis of ions produced by photon stimulated desorption. This type of analyzer can measure simultaneously differential kinetic energy, angular distribution, and mass. The design of the EMA is similar to one developed previously [D.E. Eastman, J.J. Donelon, N.C. Hien and F.J. Himpsel, Nucl. Instr. and Meth. 172 (1980) 327]. However, an entirely new approach has been used in the mechanical design, construction materials, and in the technique for charged particle position detection. The primary differences are an aberration corrected mirror, the use of titanium for the main structural components, and a resistive-anode area detector. A description of these differences and their advantages is given in detail.