Laser Imaging Techniques Research Articles

Optimization of SLIPI–polarization ratio imaging for droplets sizing in dense sprays

In this article, structured laser illumination planar imaging and polarization ratio techniques are successfully combined to size droplets in various optically dense sprays. The polarization ratio approach is based on the acquisition of the perpendicular and parallel polarized components of Lorenz–Mie scattered light, for which the ratio is proportional to the surface mean diameter, D21. One of the main advantages of this technique, compared to some other laser imaging techniques for particle sizing, is that no fluorescent dye is required. This makes the technique suitable for characterizing sprays under evaporation conditions, such as combustion or spray drying applications. In addition, the SLIPI technique aims at suppressing the detection of multiple light scattering and at extracting the desirable single-light scattering signal. To test the reliability of this novel approach, an industrial hollow-cone nozzle is used, injecting at 50 bar water mixed with Glycerol (in the range of 0–60%). The first aim of this work is to study the experimental parameters that influence the reliability of the technique, such as the polarization orientation of the incident light, the refractive index of the injected liquid and the variation of the droplet size distribution. Using Phase Doppler Anemometry, the results show that a linear calibration is obtained for droplets ranging between 10 and 70 μm, when the incident illumination has a polarization set to 10° and 20°. In addition, this article demonstrates the feasibility of the technique for the measurement of liquids having a refractive index reaching 1.41. In the last stage of this work, after rotating the nozzle every 5°, a 3D tomographic reconstruction of D21 is performed. This demonstrates the robustness and efficiency of the technique for droplet sizing in 3D, under challenging conditions.

Review on Laser Technology in Intravascular Imaging and Treatment.

Blood vessels are one of the most essential organs, which nourish all tissues in our body. Once there are intravascular plaques or vascular occlusion, other organs and circulatory systems will not work properly. Therefore, it is necessary to detect abnormal blood vessels by intravascular imaging technologies for subsequent vascular treatment. The emergence of lasers and fiber optics promotes the development of intravascular imaging and treatment. Laser imaging techniques can obtain deep vascular images owing to light scattering and absorption properties. Moreover, photothermal and photomechanical effects of laser make it possible to treat vascular diseases accurately. In this review, we present the research progress and applications of laser techniques in intravascular imaging and treatment. Firstly, we introduce intravascular optical coherent tomography and intravascular photoacoustic imaging, which can obtain various information of plaques. Multimodal intravascular imaging techniques provide more information about intravascular plaques, which have an essential influence on intravascular imaging. Secondly, two laser techniques including laser angioplasty and endovenous laser ablation are discussed for the treatment of arterial and venous diseases, respectively. Finally, the outlook of laser techniques in blood vessels, as well as the integration of laser imaging and treatment are prospected in the section of discussions.

Prediction of quality attributes and maturity classification of pear fruit using laser imaging and Artificial Neural Network

In this study, the application of laser imaging technique was utilized to predict the quality attributes (firmness and soluble solids content) of pear fruit and to classify the maturity stages of the fruit harvested at different days after full bloom (dafb). Laser imaging system emitting at visible and near infra-red region (532, 660, 785, 830 and 1060 nm) was deployed to capture the images of the fruit. Optical properties (absorption ma and reduced scattering ms ʹ coefficients) at individual and combined wavelengths of the laser images of the fruit were used in the prediction and classifications of the maturity stages. Artificial neural network (ANN) was employed in the building of both prediction and classification models. Root mean square error of calibration (RMSEC), root mean square error of crossvalidation (RMSECV), correlation coefficient (r) and bias were used to test the performance of the prediction models while sensitivity and specificity were used to evaluate the classification models. The results showed that there was a very strong correlation between the ma and ms ʹ with pear development. This study had shown that optical properties of pears with ANN as prediction and classification models can be employed to both predict quality parameters of pear and classify pear into different (dafb) non-destructively.

Computational Fluid Dynamics (CFD) as a Tool for Investigating Self-Organized Ascending Bubble-Driven Flow Patterns in Champagne Glasses.

Champagne glasses are subjected to complex ascending bubble-driven flow patterns, which are believed to enhance the release of volatile organic compounds in the headspace above the glasses. Based on the Eulerian–Lagrangian approach, computational fluid dynamics (CFD) was used in order to examine how a column of ascending bubbles nucleated at the bottom of a classical champagne glass can drive self-organized flow patterns in the champagne bulk and at the air/champagne interface. Firstly, results from two-dimensional (2D) axisymmetric simulations were compared with a set of experimental data conducted through particle image velocimetry (PIV). Secondly, a three-dimensional (3D) model was developed by using the conventional volume-of-fluid (VOF) multiphase method to resolve the interface between the mixture’s phases (wine–air). In complete accordance with several experimental observations conducted through laser tomography and PIV techniques, CFD revealed a very complex flow composed of surface eddies interacting with a toroidal flow that develops around the ascending bubble column.

Combined Experimental and CFD Approach of Two-Phase Flow Driven by Low Thermal Gradients in Wine Tanks: Application to Light Lees Resuspension.

In winemaking, clarification and stabilization are the processes by which insoluble matter suspended in the wine (called lees) is removed before bottling. The light lees represent 2–4% of the total wine volume. Under certain circumstances, resuspension of lees may occur. The resuspension of lees has been attributed to temperature variations between the wine stored in tanks and the environment of the cellar. From in situ, laboratory-scale studies involving laser tomography techniques, it was shown that low (positive or negative) thermal gradients between a wine tank containing light lees and its external environment induce mass transfer by natural convection. To extrapolate these findings to full-scale tanks, an Eulerian-Eulerian multiphase CFD model was applied to simulate the two-phase flow behavior as a function of temperature variations on a 24–h cycle. Numerical temperature and time-dependent flow patterns of both wine and lees confirm that low thermal gradients induce sufficient fluid energy to resuspend the lees, thus showing that the laboratory results can be extrapolated to full-scale tanks.

Turbulent Flames in Enclosed Combustion Chambers: Characteristics and Visualization—A Review

AbstractRemarkable progress has been achieved in measuring the flame propagation rate accurately under laminar conditions, which can be used to predict turbulent flame propagation rates using some correlations fitted to experimental data. However, such propagation rates, unlike the laminar case, cannot be unambiguously determined. Nevertheless, the advancement of laser imaging techniques has led to several definitions of turbulent burning rates (Roshan et al., 2010, “Simulation of Global Warming Effect on Outdoor Thermal Comfort Conditions,” Int. J. Environ. Sci. Technol., 7(3), pp. 571–580). Recently, a unified scaling factor has been successfully demonstrated using data gathered from several fan-stirred bombs. Such results are promising in compiling a comprehensive database of turbulent propagation rates for potential and common fuels of interest to internal combustion engines (ICEs) and gas turbines alike. The strict worldwide legislation to reduce emissions has forced many industries to look into alternative fuels with less emissions. One such alternative fuel that has gained much interest recently is the gas-to-liquid (GTL) fuel, which is being used in blended forms in several combustion applications. However, detailed combustion characteristic investigations are required before using this new alternative fuel widely in engines (Business, 2018, “Qatar’s Exporters Directory 2018”). In this study, the significant issues associated with the use of fan-stirred bombs are investigated. First, the effect of varying fan speed and geometry is reviewed, and then, the measurement techniques that are commonly used to track flame propagation are discussed. This is followed by the study of the effect of using different types of fuels on combustion characteristics. Furthermore, the use of diesel and gasoline optical engine setups as advanced flame visualization tools have been reviewed extensively.

Passive wine macromixing from 3D natural convection for different winery tank shapes: application to lees resuspension

The works presented in this paper aim at investigating the problems related to the clarification of wines when random passive resuspension of lees occurs. More precisely, resuspension is addressed when temperature variations occur between the wine stored in tanks and the external surroundings of the tanks. From in situ laboratory studies involving laser tomography techniques, it is shown that low temperature gradients between a wine containing light lees and its external environment induce mass transfer by natural convection, generating enough fluid energy to resuspend the light lees in the liquid phase. The experiments are then complemented by numerical, CFD-based simulations focused on the role played by the geometry of different commercial tanks in the intensity of internal mixing. Finally, the groundwork for a study on a new internal design of the tanks by helical grooving is presented. To the best of the authors' knowledge, no literature study mentions the influence of thermal gradients on the resuspension of light lees and the influence of winery tank shapes on the internal fluid mixing intensity.

Monitoring of scaling in dilute phase pneumatic conveying systems using non-intrusive acoustic sensors – A feasibility study

Scale formation in pneumatic conveying systems is a major industrial challenge. The underlying scale formation mechanisms can be intricate as they often involve a combination of several mutually enhancing binding forces and can be affected by a number of different factors. A non-intrusive monitoring technique capable of measuring scale growth would be a valuable tool to investigate different scaling mechanisms. In this study, the feasibility of an active acoustic sensor technique for monitoring of scale growth in a pneumatic conveying system is evaluated. Tests are performed in a pilot scale pneumatic conveying system transporting sand in dilute phase. The acoustic sensors conducts measurements on test pipes which are coated with a primer/powder mixture, one layer after the other, to simulate scale progression. Reference measurements of the coating layer thickness in the test pipes are obtained by a laser imaging technique for each added coating layer. A multivariate method is used to calibrate prediction models of the scale thickness using acoustic measurements as independent variables and the reference measurements as the dependent variable. Results show that the active monitoring method is capable of monitoring scale growth in pneumatic conveying systems and that dilute phase conveying of sand does not affect the precision of predictions made by the method.

Microvascular involvement in systemic sclerosis and systemic lupus erythematosus.

Microvascular changes play central roles in the pathophysiology of SSc and SLE, and represent major causes of morbidity and mortality in these patients. Therefore, clinical tools that can assess the microvasculature are of great importance both at the time of diagnosis and follow-up of these cases. These tools include capillaroscopy, laser imaging techniques, infrared thermography, and iontophoresis. In this review, we examined the clinical manifestations and pathobiology of microvascular involvement in SSc and SLE as well as the methodologies used to evaluate the microvasculature.

Application of laser biospeckle technique for the analysis of artificially introduced local dynamics in apple fruit

Laser biospeckle technique has been extensively used as a significant characterization tool to analyze the complex inner dynamics involved in both biological and non-biological processes. The technique has been widely applied in the field of biology, medicine and agriculture as well as in the chemical and pharmaceutical industries. Among the challenges in biology or agriculture, one of the tasks is the assessment of the local dynamics of biological specimens. We report on an optical imaging technique, the laser biospeckle to assess the local dynamics introduced on selected biological specimens subjected to mechanical and thermal loads. This study also aimed to explore the technique in detecting the early stages of biological activities. An experimental configuration of the biospeckle laser imaging technique was used to assess the monitoring and prediction of the bruising on fruit surfaces within a specified time. The methods utilized to interpret the biospeckle data allowed pre-disposition detection of the formation of internal bruising in the early stages after the occurrence of a mechanical or thermal impact.

Assessment of biological leaf tissue using biospeckle laser imaging technique

We report on the application of an optical imaging technique, the biospeckle laser, as a potential tool to assess biological and medicinal plant leaves. The biospeckle laser technique is a non-invasive and non-destructive optical technique used to investigate biological objects. Just after their removal from plants, the torn leaves were used for biospeckle laser imaging. Quantitative evaluation of the biospeckle data using the inertia moment (IM) of the time history speckle pattern, showed that the IM can be utilized to provide a biospeckle signature to the plant leaves. It showed that leaves from different plants can have their own characteristic IM values. We further investigated the infected regions of the leaves that display a relatively lower biospeckle activity than the healthy tissue. It was easy to discriminate between the infected and healthy regions of the leaf tissue. The biospeckle technique can successfully be implemented as a potential tool for the taxonomy of quality leaves. Furthermore, the technique can help boost the quality of ayurvedic medicines.

Iron meteorite bulk densities determined via 3‐D laser imaging

AbstractThis study tested the feasibility of using 3‐D laser imaging to measure the bulk density of iron meteorites. 3‐D laser imaging is a technique in which a 3‐D model of an object is built after aligning and merging individual detailed images of its surface. Assuming that the mass of the object is known, the volume of the model is calculated by software and an estimate of bulk density can be obtained by dividing mass by volume. The 3‐D laser imaging technique was used to determine the density of 46 fragments from 11 different iron meteorites. The technique proved to be robust and was applied successfully to study samples ranging close to four orders of magnitude in mass (8 g to 156 kg) and exhibiting a variety of surface textures (e.g., cracks, regmaglypts), reflectivities (e.g., polished surfaces, fusion crust, rust), and morphologies (e.g., sharp angular edges, shrapnel tendrils). Three metrics were considered to estimate the error associated with density measurements: the range accuracy of the laser camera, image alignment error, and inter‐operator variability during model building. Inter‐operator variability was the largest source of error and was highest when assembling models of samples which either lacked distinctive features or were very complex in shape. Excluding two anomalous Zagora samples where silicate inclusions might have lowered density, the densities measured using 3‐D laser imaging ranged from 6.98 to 7.93 g cm−3, consistent with previous studies. There is overlap between bulk density and iron meteorite class, and therefore bulk density cannot be used in isolation as a classification criterion. It is a good indicator, however, of weathering effects and of the potential presence of low‐density inclusions.

Measurements Methods for the analysis of Nuclear Reactors Thermal Hydraulic in Water Scaled Facilities

The Belgian nuclear research institute (SCK•CEN) is developing MYRRHA. MYRRHA is a flexible fast spectrum research reactor, conceived as an accelerator driven system (ADS). The configuration of the primary loop is pool-type: the primary coolant and all the primary system components (core and heat exchangers) are contained within the reactor vessel, while the secondary fluid is circulating in the heat exchangers. The primary coolant is Lead Bismuth Eutectic (LBE). The recent nuclear accident of Fukushima in 2011 changed the requirements for the design of new reactors, which should include the possibility to remove the residual decay heat through passive primary and secondary systems, i.e. natural convection (NC). After the reactor shut down, in the unlucky event of propeller failures, the primary and secondary loops should be able to remove the decay heat in passive way (Natural Convection). The present study analyses the flow and the temperature distribution in the upper plenum by applying laser imaging techniques in a laboratory scaled water model. A parametric study is proposed to study stratification mitigation strategies by varying the geometry of the buffer tank simulating the upper plenum.

The changing landscape of dermatology practice: melanoma and pump-probe laser microscopy.

To present current melanoma diagnosis, staging, prognosis, and treatment algorithms and how recent advances in laser pump-probe microscopy will fill in the gaps in our clinical understanding. Expert opinion and significantly cited articles identified in SCOPUS were used in conjunction with a pubmed database search on Melanoma practice guidelines from the last 10years. Significant advances in melanoma treatment have been made over the last decade. However, proper treatment algorithm and prognostic information per melanoma stage remain controversial. The next step for providers will involve the identification of patient population(s) that can benefit from recent advances. One method of identifying potential patients is through new laser imaging techniques. Pump-probe laser microscopy has been shown to correctly identify nevi from melanoma and furthermore stratify melanoma by aggressiveness. The recent development of effective adjuvant therapies for melanoma is promising and should be utilized on appropriate patient populations that can potentially be identified using pump-probe laser microscopy.

Low-cost optical approach for noncontact predicting moisture content of apple slices during hot air drying

ABSTRACTAbsorption and scattering properties of product change as moisture content is reduced, but it has not been investigated how these changes are correlated. This study was aimed to measure and test the feasibility of using optical properties in predicting the moisture content of sliced apple samples during hot air drying. In this investigation, the noninvasive backscattering laser imaging technique at three wavelengths (650, 780, and 880 nm) and Farrell’s diffusion theory were used to determine absorption and reduced scattering coefficients. Artificial neural network model was applied to correlate the optical coefficients and moisture content of samples. The highest correlation between above-mentioned parameters was found at 780 nm. The best moisture content prediction result was obtained when absorption and reduced scattering coefficients were combined at three wavelengths with Rp = 0.984. The results suggested that this method can be effectively used to predict the moisture content and control the drying process.

In vivo multiphoton-microscopy of picosecond-laser-induced optical breakdown in human skin.

ImportanceImprovements in skin appearance resulting from treatment with fractionated picosecond‐lasers have been noted, but optimizing the treatment efficacy depends on a thorough understanding of the specific skin response. The development of non‐invasive laser imaging techniques in conjunction with laser therapy can potentially provide feedback for guidance and optimizing clinical outcome.ObjectiveThe purpose of this study was to demonstrate the capability of multiphoton microscopy (MPM), a high‐resolution, label‐free imaging technique, to characterize in vivo the skin response to a fractionated non‐ablative picosecond‐laser treatment.Design, Setting, and ParticipantsTwo areas on the arm of a volunteer were treated with a fractionated picosecond laser at the Dermatology Clinic, UC Irvine. The skin response to treatment was imaged in vivo with a clinical MPM‐based tomograph at 3 hours and 24 hours after treatment and seven additional time points over a 4‐week period.Main Outcomes and MeasuresMPM revealed micro‐injuries present in the epidermis. Pigmented cells were particularly damaged in the process, suggesting that melanin is likely the main absorber for laser induced optical breakdown.ResultsDamaged individual cells were distinguished as early as 3 hours post pico‐laser treatment with the 532 nm wavelength, and 24 hours post‐treatment with both 532 and 1064 nm wavelengths. At later time points, clusters of cellular necrotic debris were imaged across the treated epidermis. After 24 hours of treatment, inflammatory cells were imaged in the proximity of epidermal micro‐injuries. The epidermal injuries were exfoliated over a 4‐week period.Conclusions and RelevanceThis observational and descriptive pilot study demonstrates that in vivo MPM imaging can be used non‐invasively to provide label‐free contrast for describing changes in human skin following a fractionated non‐ablative laser treatment. The results presented in this study represent the groundwork for future longitudinal investigations on an expanded number of subjects to understand the response to treatment in different skin types with different laser parameters, critical factors in optimizing treatment outcome. Lasers Surg. Med. 49:555–562, 2017. © 2017 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Target reconstruction algorithm for four-beam sheared coherent imaging

Sheared-beam imaging, which is a nonconventional coherent laser imaging technique, can be used to better solve the problem of taking pictures with high resolution for remote targets through turbulent medium than conventional optical methods. In the previous research on this technique, a target was illuminated by three coherent laser beams that were laterally arranged at the transmitter plane into an L pattern. In order to obtain a high quality image, a series of time-varying scattered signals is collected to reconstruct speckled images of the same object. To overcome atmospheric turbulence, multiple sets of three-beam laser should be emitted, which increases data acquisition time. In this paper, aiming at the quasi real-time problem of conventional sheared beam imaging technique, we use four-beam laser with rectangular distribution instead of the traditional L type sheared three-beam laser to illuminate the target. According to this, we propose a target reconstruction algorithm for four-beam sheared coherent imaging to reconstruct four target images simultaneously in one measurement, which can acquire high quality images by reducing the amount of measurement and the speckle noise. Meanwhile, it can greatly reduce the amount of beam switching in multi-group emission and improve the imaging efficiency. Firstly, the principle of the four-beam sheared coherent imaging technique is deduced. Secondly, in the algorithm, the speckle amplitude and phase difference frames can be extracted accurately by searching for the accurate positions of the beat frequency components. Based on the speckle phase difference frames, four sets of wavefront phases can be demodulated by the least squares method, and wavefront amplitude can be obtained by algebraic operation of speckle amplitude. The reconstructed wavefront is used for inverse Fourier transform to yield a two-dimensional image. A series of speckled images is averaged to form an incoherent image. Finally, the validity of the proposed technique is verified by simulations. From the simulation results, the image quality of the proposed method is better than that of the traditional method in the same amount of measurement. Furthermore, on the premise of the same image quality, the data acquisition amount of the proposed method is 2-3 times as large as that of the traditional method. In other words, compared with that of the traditional method, the data acquisition time of the proposed method is reduced at least by half and the algorithm processing time is less. It can be concluded that the proposed imaging technique can not only improve the efficiency of target reconstruction, but also present a better way of imaging the remote moving targets.

Dynamics of diffusive and convective transport in porous media: A fractal analysis of 3-D images obtained by laser technology

The objective of this paper was to use laser imaging technique to visualize the diffusion controlled mass transfer process in porous media. Cubical models made of different materials (oil-wet plexiglass and water wet glass) and filled with 1mm and 4mm glass beads and different types of oils were used to visualize the -Fickian- diffusion of solvent with different densities and viscosities. 3-D visualization technique with laser sheet scanning of refractive index matched glass-bead-pack model was used to study the effect of permeability, solvent density, viscosity and boundary effect on mixing by diffusion. Three types of solvents were used: (1) solvent with density higher than oil but low viscosity, (2) solvent lighter than oil but has high viscosity, and (3) solvent lighter but less viscous than oil.It was observed through 3-D images obtained from the experiments that the width (area) of the solvent swept region and fingering depended on the density of the solvent and the speed of the process was higher in the high permeability porous media (4mm glass beads). Wider fingers and swept areas were observed for less viscous solvent. Solvents 1 and 2 slowly mixed and rose to the top of the model filling most of the pores in the model, and then diffused into the unswept region. Solvent 3 reached the top of the model in an extremely short time along the boundary with thin fingering and displaces downward afterwards. The frontal progresses of solvent-oil interfaces (mixing zone) were analyzed quantitatively through the change of the fractal dimension during the process. The fractal dimension increased before the solvent reached at the top of the model. For solvents 1 and 2, the fractal dimension decreased afterward. For solvent 3, the value declined rapidly because the solvent took time to spread along the top of the model due to its extremely low viscosity and density.

Flow patterns and mixing characteristics of horizontal buoyant jets at low and moderate Reynolds numbers

Laminar horizontal buoyant jets have been found to exhibit peculiar behavior of unstable nature, e.g., bifurcation in the form of a vertical secondary plume deriving from the primary jet, due to the unstable stratification on one half of circumferential interface between the jet and the ambient fluid. However, whether and how this exceptional unstable jet behavior persists into the transitional regime with moderate Reynolds numbers (500<Re<2000) remains an open question. In this study, we explored the flow pattern and stability, i.e., the tendency to bifurcate, of horizontal buoyant jets with different densimetric Froude number (Fr) extending from low to moderate Reynolds numbers in the laboratory. The non-intrusive laser imaging technique of Planar Laser Induced Fluorescence (PLIF) was employed for the flow visualization and measurements. Three distinct flow patterns characterized with unstable small-scale structures, namely, ‘primary jet with vertical secondary plume’, ‘primary jet with pseudo secondary jet’ and ‘quasi-turbulent horizontal buoyant jet’, were identified in the Re–Fr parameter space determined from the visualization results. The substantive bifurcation reported earlier in the literature based on shadowgraph imaging was however not observed within the presumptive space in the present experiments. Quantitative concentration measurements using PLIF were further analyzed to study the jet mixing and spreading characteristics in the laminar and transitional regimes, including the decay of maximum concentration along the jet centerline, the cross-sectional concentration distribution at different downstream locations, as well as the concentration spread. Remarkably, the concentration decay/spreading rates exhibited a first-decreasing-then-increasing/first-increasing-then-decreasing behavior respectively with Re within the test range, reconciling the contradictory trends reported in the literature and suggesting the existence of a Re threshold below which the viscous force will prevail and suppress the potentially enhanced mixing and entrainment of low Re jet due to its less uniformity and coherence. Beyond the threshold, strong correlation of the concentration decay and spreading coefficients with Fr also confirmed that the jet mixing and spreading are dependent on the buoyancy-generated turbulence. Overall, the experimental results provided new insight on the flow patterns and mixing characteristics of horizontal buoyant jets in the laminar and transitional regimes.

Experimental investigation of the passage of fuel droplets through a spherical two-phase flame

This paper reports experimental studies of two-phase combustion carried out with an aerosol of mono-sized ethanol droplets generated by rapid expansion under microgravity conditions. Optical diagnostics consisting of coupling laser tomography with the high-speed ILIDS technique are successfully applied for the aerosol combustion study. Droplet diameter reduction together with the radial droplet displacement ahead of the flame front is accurately measured. It is found that fuel droplets evaporate by following the d2 law which confirms the validity of this model in an aerosol configuration. The laser tomography technique allows the identification of droplets which are present in the burnt gases. A regime diagram has been built using relevant non-dimensional parameters of two-phase combustion to exhibit the observations of droplets crossing. The results demonstrate that the droplet size and the droplet interdistance are the most important parameters which control the possibility for the droplet to penetrate the burnt gases. Moreover, it is observed that typical topologies of flames in terms of size and number of cells are related to the droplet number density.