Accurate Optical Method Research Articles

Optical Interferometric Device for Rapid and Specific Detection of Biological Cells.

Here, we report a rapid and accurate optical method for detecting cells from liquid samples in a label-free manner. The working principle of the method is based on the interference of parts of a conical laser beam, coming from a single-mode optical fiber directly, and reflected from a flat glass surface. The glass is functionalized by antibodies against the cells to be detected from the liquid sample. Cells bound to that surface modify the reflected beam, and hence, change the resulting interference pattern, too. By registering and interpreting the variation in the image, the presence of cells from the sample can be detected. As for a demonstration, cell suspensions from a U937 cell line were used in glass chambers functionalized by antibodies (TMG6-5 (mIgG1)) to which the cells specifically bind. The limit of detection (LOD) of the method was also estimated. This proof-of-concept setup offers a cost-effective and easy-to-use way of rapid and specific detection of any type of cells (including pathogens) from suspensions (e.g., body fluids). The possible portability of the device predicts its applicability as a rapid test in clinical diagnostics.

Elevation Resolution Enhancement Oriented 3D Ultrasound Imaging.

Three-dimensional (3D) ultrasound imaging can be accomplished by reconstructing a sequence of two-dimensional (2D) ultrasound images. However, 2D ultrasound images usually suffer from low resolution in the elevation direction, thereby impacting the accuracy of 3D reconstructed results. The lateral resolution of 2D ultrasound is known to significantly exceed the elevation resolution. By combining scanning sequences acquired from orthogonal directions, the effects of poor elevation resolution can be mitigated through a composite reconstructing process. Moreover, capturing ultrasound images from multiple perspectives necessitates a precise probe positioning method with a wide angle of coverage. Optical tracking is popularly used for probe positioning for its high accuracy and environment-robustness. In this paper, a novel large-angle accurate optical positioning method is used for enhancing resolution in 3D ultrasound imaging through orthogonal-view scanning and composite reconstruction. Experiments on two phantoms proved that our method could significantly improve reconstruction accuracy in the elevation direction of the probe compared with single-angle parallel scanning. The results indicate that our method holds the potential to improve current 3D ultrasound imaging techniques.

Proposing an Accurate and Fast Optical Batch Inspection Method of Mini-/Micro-LEDs

Proposing an Accurate and Fast Optical Batch Inspection Method of Mini-/Micro-LEDs

A simple and highly accurate method for fuzzy edge-based 3D morphometry

As the level of engineering technology increases, the mechanical problems posed in the area of mechanics become complex and diverse. The traditional measurement methods and content of past measurements no longer meet the needs, so more advanced experimental methods are needed to accurately measure the three-dimensional shape of objects and their deformations. Nitrate ester plasticized polyether (NEPE) propellants, are the highest energy solid propellant that have been applied in public reports in the world. Due to the material properties of the material itself, its mechanical properties cannot be accurately measured by conventional methods. This paper proposes a simple and highly accurate optical measurement method to study the volume change rate, Poisson’s ratio and true stress-strain curves of NEPE at different displacement loading rates of NEPE. In this paper, the strain of solid propellant NEPE in three directions during unidirectional stretching was measured by defocusing method and digital image correlation(DIC) method and the volume change rate, Poisson’s ratio and true stress-strain curves of NEPE under different stretching rates were obtained. The measured damage initiation engineering strain of NEPE at different tensile strain rates is 0.4687.

Discrimination between normal and cancer white blood cells using holographic projection technique.

White blood cells (WBCs) play a vital role in the diagnosis of many blood diseases. Such diagnosis is based on the morphological analysis of blood microscopic images which is performed manually by skilled hematologist. However, this method has many drawbacks, such as the dependence on the hematologist’s skill, slow performance, and varying accuracy. Therefore, in the current study, a new optical method for discrimination between normal and cancer WBCs of peripheral blood film (PBF) images is presented. This method is based on holographic projection technique which is able to provide an accurate and fast optical reconstruction method of WBCs floating in the air. Besides, it can provide a 3D visualization map of one WBC with its characterization parameters from only a single 2D hologram. To achieve that, at first, WBCs are accurately segmented from the microscopic PBF images using a developed in-house MATLAB code. Then, their associated phase computer-generated holograms (CGHs) are calculated using the well-known iterative Fourier transform algorithm (IFTA). Within the utilized algorithm, a speckle noise reduction technique, based on temporal multiplexing of spatial frequencies, is applied to minimize the speckle noise across the reconstruction plane. Additionally, a special hologram modulation is added to the calculated holograms to provide a 3D visualization map of one WBC, and discriminate normal and cancer WBCs. Finally, the calculated phase-holograms are uploaded on a phase-only spatial light modulator (SLM) for optical reconstruction. The optical reconstruction of such phase-holograms yields precise representation of normal and cancer WBCs. Moreover, a 3D visualization map of one WBC with its characterization parameters is provided. Therefore, the proposed technique can be used as a valuable tool for interpretation and analysis of WBCs, this in turn could provide an improvement in diagnosis and prognosis of blood diseases.

Highly accurate optical flow method based on volumetric segmentation for 3D PIV

In this study, we present a new three-dimensional optical flow method based on volumetric segmentation for the velocity estimation of fluid flow. The proposed method uses a segmented smoothness term that is designed on the assumption that the particle velocity varies continuously in each segmented volume and discontinuously on the surfaces of the segmented volumes. Subsequently, the data term is proposed on the basis of the segmented volumes and the fluid mass conservation equation, which is derived from the Reynolds transport equation. In addition, the robust local level-set method is applied to segment the particle volume according to the velocity distribution of fluid flow. The proposed method is evaluated quantitatively on synthetic data and qualitatively on experimental data, and the velocity results are compared to the advanced 3D velocity estimation methods. The results indicate that the proposed method can obtain velocity fields with greater measurement accuracy for Tomo-PIV.

Accurate optical simulation method of tandem organic light-emitting diode with consideration of Purcell effect

In this paper, we report an accurate optical calculation method of tandem organic light-emitting diode (OLED) with consideration of Purcell effect. Using the normal reported method, there are some discrepancies between calculation and experimental external quantum efficiencies. To improve such discrepancies, we considered Purcell effect in optical calculation method. This improved calculation with Purcell effect were well matched with experimental results. Additionally, we measured exciton lifetime to identify the validity of Purcell factor which was applied to calculation. Through this measurement, we identified theoretical calculation is well matched with experimental tendency. Thus, this calculation can be more useful in tandem OLED applications.

The particle image tracking technique: An accurate optical method for measuring individual kinematics of rigid particles

AbstractWe present a new approach to assess the two‐dimensional motion of rigid bodies in granular materials. Although it was adapted from digital image correlation technique, the heart of the presented technique relies on specific treatments related to the discrete nature of grain‐displacement fields. The code called Tracker has been developed to process the digital images and measure the in‐plane displacement and rotation of each individual grain from one image to another. A remarkable feature is the use of a specific strategy that allows tracking all particles, without losing any of them (which is a typical problem when tracking assemblies of discrete particles over many images). This is achieved by a two‐step procedure, where, in case of problematic tracking of a grain, the size of the search zone is increased in an adaptive manner, that is, taking into account the results of tracking in the neighbourhood of the particle. The accuracy of the measured displacements and rotations was tested on both perfect synthetic images and digital photographs of a sheared assembly of grains. An automatic procedure that corrects the lens distortion further improves the quality of the measurements. The accurate assessment of the grain kinematics opens very interesting perspectives, especially in the study of displacement fluctuations in granular media.

Spectroscopic ellipsometric investigation of optical parameters of oil-water thin multiple systems

To determine the optical parameters of crude oil and seawater systems, we carried out spectral investigations using the ellipsometry method, which is a highly sensitive and accurate optical method for studying the surfaces and interfaces of various media. This method is based on studying the change in the polarization state of reflected light after its interaction with the surface of interfaces of these media. Crude oil and seawater from different regions of Caspian Sea were accessed by spectroscopic ellipsometry over the 200–1700 nm spectral range at room-temperature. Optical constants and dielectric function were obtained for massive samples of each substance, as well as for ultrathin layers of the oil spilled over the sea surface. Dielectric function, when completely determined in the frequency regions corresponding to electronic transitions and excitation of atomic or molecular vibrations in the object, is a unique dielectric fingerprint of this object. Oils with even miserable difference in type and concentration of biomarkers and heterocomponents will have different dielectric functions. The possibility to use dielectric function as a unique optical fingerprint for oil identification is figured out.

Azimuthal Alignment Method for Optimizing Bragg Grating Inscription in Photonic Crystal Fibers

An accurate (≤5°) and straightforward implementation optical method for determining the azimuthal lattice orientation of a microstructured optical fiber with respect to the side illumination beam used for Bragg grating recording is presented. This method is based on the diffraction pattern generated backward of the photonic crystal fiber cladding upon a continuous-wave visible laser light illumination. This optical fiber alignment and coordination method is experimentally demonstrated, describing in detail characteristic light scattering patterns used for the azimuthal orientation of the fiber with respect to the side-coming laser beam. Moreover, this alignment method is theoretically validated using standard ray tracing beam scattering software. Bragg grating recordings performed in this photonic crystal fiber (PCF) using 193-nm excimer laser radiation are also presented to depict the impact of the azimuthal alignment of the fiber with the inscription beam on the photosensitivity refractive index changes induced in the optical fiber.

Chlorophyll Fluorescence and Reflectance-Based Non-Invasive Quantification of Blast, Bacterial Blight and Drought Stresses in Rice.

Response of rice (Oryza sativa) exposed to both biotic and abiotic stresses can be quantified by employing fast and accurate optical methods. In this study, the overall stress responses of (i) 12 near-isogenic lines (NILs) in the genetic background of the rice blast-susceptible cultivar Lijiangxintuanheigu (LTH) and (ii) four NILs in the genetic background of the bacterial blight-susceptible cultivar IR24, were inspected by means of Chl fluorescence (Chl-F) imaging. The distribution of the maximum and effective quantum yield of PSII (Fv/FM and QY) and steady-state Chl-F (Ft) were found to be effective in differentiating symptomatic leaf tissue for both rice blast and bacterial blight, which correlated well with 30 cycles of rice blast and six cycles of bacterial blight previously screened using classical (manual) approaches. Subsequently, identified Chl-F parameters allowing detection under ambient light (QY and Ft) were tested across both biotic and abiotic (drought) stress experiments, for rice cultivars contrasting for drought stress response (N22, IR64 and NSIC Rc 222). Their applicability has been proven for both rice blast and bacterial blight; however, QY failed to detect the effect of drought. In addition to Chl-F, the usefulness of 11 selected vegetation indices (Vis) was tested on these three cultivars exposed to particular stresses: (i) rice blast was detectable by Vis calculated from the visible spectrum; (ii) bacterial blight by near-infrared-related Vis; and (iii) drought by Vis calculated from the visible spectrum. The key Chl-F parameters and/or Vis have been summarized and discussed.

An accurate optical method for the measurement of contact angle and interface shape of evaporative thin liquids films

The aim of this study was to present an original method to compute the shape of the interface in the vicinity of the contact line after liquid film breakup. The liquid film is a controlled volume of evaporating liquid (HFE7100) filling a millimetric cylindrical vertical well. During the evaporation process, the liquid-gas interface takes on a toroidal shape delimiting an axisymmetric liquid meniscus (together with the well bottom and side walls). The first step of the evaporation process occurs without a contact line on the bottom and is followed, in the second step, by the creation and growth of a dry patch delimited by a circular contact line on the well bottom. The shape of the meniscus interface and the position of the contact line are instantaneously measured by laser sheet sounding from below and numerical inversion. This technique determines the variation of the light intensity of a laser sheet due to its refraction through consecutive interfaces (solid-liquid-vapor).The intensity of the laser sheet impact on a perpendicular screen is inverted. The inversion results provide the shape of the interface and the position of the contact line during the evaporation process. By this new method contact angles between 2 and 40 degrees can be measured and the interface shape can be obtained with high accuracy. This method is specially adapted for concave shape, as meniscus, where side view is not possible. It is perfectly complementary with the other classical methods (e.g., interferometry and goniometry).

High-precision micro-displacement optical-fiber sensor based on surface plasmon resonance.

We propose and demonstrate a novel optical-fiber micro-displacement sensor based on surface plasmon resonance (SPR) by fabricating a Kretschmann configuration on graded-index multimode fiber (GIMMF). We employ a single-mode fiber to change the radial position of the incident beam as the displacement. In the GIMMF, the angle between the light beam and fiber axis, which is closely related to the resonance angle, is changed by the displacement; thus, the resonance wavelength of the fiber SPR shifts. This micro-displacement fiber sensor has a wide detection range of 0-25μm, a high sensitivity with maximum up to 10.32nm/μm, and a nanometer resolution with minimum to 2nm, which transcends almost all of other optical-fiber micro-displacement sensors. In addition, we also research that increasing the fiber polishing angle or medium refractive index can improve the sensitivity. This micro-displacement sensor will have a great significance in many industrial applications and provide a neoteric, rapid, and accurate optical measurement method in micro-displacement.

Spectrophotometric method for optical band gap and electronic transitions determination of semiconductor materials

The optical band gap energy and the electronic processes involved are important parameters of a semiconductor material and it is therefore important to determine their correct values. Among the possible methods, the spectrophotometric is one of the most common. Several methods can be applied to determine the optical band gap energy and still now a defined consensus on the most suitable one has not been established. A highly diffused and accurate optical method is based on Tauc relationship, however to apply this equation is necessary to know the nature of the electronic transitions involved commonly related to the coefficient n. For this purpose, a spectrophotometric technique was used and we developed a graphical method for electronic transitions and band gap energy determination for samples in powder form. In particular, the n coefficient of Tauc equation was determined thorough mathematical elaboration of experimental results on TiO2 (anatase), ZnO, and SnO2. The results were used to calculate the band gap energy values and then compared with the information obtained by Ultraviolet Photoelectron Spectroscopy (UPS). This approach provides a quick and accurate method for band gap determination through n coefficient calculation. Moreover, this simple but reliable method can be used to evaluate the nature of electronic transition that occurs in a semiconductor material in powder form.

Optical bandgap of single- and multi-layered amorphous germanium ultra-thin films

Accurate optical methods are required to determine the energy bandgap of amorphous semiconductors and elucidate the role of quantum confinement in nanometer-scale, ultra-thin absorbing layers. Here, we provide a critical comparison between well-established methods that are generally employed to determine the optical bandgap of thin-film amorphous semiconductors, starting from normal-incidence reflectance and transmittance measurements. First, we demonstrate that a more accurate estimate of the optical bandgap can be achieved by using a multiple-reflection interference model. We show that this model generates more reliable results compared to the widely accepted single-pass absorption method. Second, we compare two most representative methods (Tauc and Cody plots) that are extensively used to determine the optical bandgap of thin-film amorphous semiconductors starting from the extracted absorption coefficient. Analysis of the experimental absorption data acquired for ultra-thin amorphous germanium (a-Ge) layers demonstrates that the Cody model is able to provide a less ambiguous energy bandgap value. Finally, we apply our proposed method to experimentally determine the optical bandgap of a-Ge/SiO2 superlattices with single and multiple a-Ge layers down to 2 nm thickness.

Near-field radiative heat transfer between two parallel SiO2 plates with and without microcavities

Near-to-far-field radiative heat transfer between two macroscopic SiO2 plates—with and without microcavities—was observed using a highly precise and accurate optical gap-measurement method. The experiments, conducted near 300 K, measured heat transfer as a function of gap separation from 1.0 μm to 50 μm and also as a function of temperature differences between 4.1 and 19.5 K. The gap-dependent heat flux was in excellent agreement with theoretical predictions. Furthermore, the effects of microcavities on the plate surfaces were clearly observed and significant enhancement of near-field radiative heat transfer was confirmed between gold-coated microcavities with narrow vacuum separation.

Spectral analysis of ship waves in deep water from accurate measurements of the free surface elevation by optical methods

This paper details the spectral analysis of the waves generated from an experimental study of the water surface elevation around a ship model in a towing tank. The wave pattern is measured with accurate optical methods in deep-water conditions for various Froude numbers. These optical methods allow the entire wave field around the model with a high spatial resolution to be obtained. The quality of the measured surface elevation around the ship model enables us to perform a spectral analysis of the waves generated by a ship. To validate this approach, the experimental spectrum is compared to the fundamental theoretical dispersion relation of the waves generated by a moving perturbation in calm deep water. In a second step, a fundamental decomposition of the wave system is achieved, from which the contribution of the near field, the local flow disturbance, and the contribution of the far field that corresponds to the Kelvin wake system are computed. In addition, the experimental extraction of the dispersion relation provides an estimate of the angle of the cone of the Kelvin wake in the spectral space.

Polarimetric Imaging for Cancer Diagnosis and Staging

A medical imaging technique that relies on light polarization could become a fast and accurate optical method for detecting cancer and determining the stage of the disease.

Monitoring and dynamic control of distance and tilt angle measurements in micro-alignment instrument using an imaging approach

An accurate and simple optical triangulation method is proposed for determining the distance and the tilt angle between the window and the SQUID sensor in a scanning SQUID microscope (SSM) system. The surface of window near the sensor plane is roughened with Alumina powder so that the incident and reflected traces of the laser beam passing the window surface become visible and can be measured precisely with a normal optical microscope. Using the proposed approach, the distance between the sensor and the sample can be reproducibly adjusted to 30 microm or less. This method can also be applied to photolithography apparatus to detect the relative positions of the mask and the wafer.

Improved Optical Pulse Characterization Based on Feedback-Controlled Hilbert Transformation Temporal Interferometry

We propose an accurate ultrashort optical pulse reconstruction method based on Hilbert transform temporal interferometry with a feedback control technique. The use of this feedback control allows us to minimize the phase measurement errors associated with instabilities in the fiber-based interferometry system, e.g., caused by environmental fluctuations. The method is experimentally demonstrated by precisely characterizing picosecond pulses after linear dispersion through short sections (30 ~ 700 m) of conventional single-mode fiber. A three-fold improvement in the phase measurement accuracy has been achieved using the feedback control technique.