Laser Profile Research Articles

Experimental investigation of spooling test on the multilayer oceanographic winch with high-performance synthetic fibre rope

Compared with steel wire ropes, synthetic fibre ropes have a better performance in deep sea and gradually replaced the former in subsea launch and recovery systems. However, serious damage will be introduced to the winch structure when synthetic fibre ropes wound in multiple layers on the winch drum. In order to comprehensively explore the relationship between the mechanical properties of the winch drum barrel and the synthetic fibre rope, biaxial strain gauges and laser profile scanners have been used to monitor the oceanographic winch using a high-modulus polyethylene (HMPE) rope with the length of 13000 m. The full-size test rig was first introduced as an attempt to quantify the effect of winding fibre rope and evaluate the stresses on the winch with multilayer winding fibre rope. The results reveal that a loss elimination effect on rope windings may occur during the spooling experiment of fibre rope owing to the hysteresis property of the fibre, which differs significantly from the results published previously. Moreover, a more concise winding model is developed to estimate the spoolingand deformation states of the synthetic fibre rope, which can well simulate the cross-section deformation of the wound HMPE rope.

Evaluation of Tunnel Contour Quality Index on the Basis of Terrestrial Laser Scanning Data

Abstract The Tunnel Contour Quality Index (TCI) is an index established by Kim and Bruland for an effective management of a tunnel contour quality. It is estimated on a basis of measurements of two contour profiles within a single blasting round, using a laser profiler. However, the representativeness of measurement results obtained that way for the assessment of a contour quality of the entire blasting round is disputable. Terrestrial laser scanning (TLS) technology, combined with available numerical surface modeling tools, enables development of three-dimensional models of a monitored surface. The article reports results of TCI calculations based on TLS data. The presented TLS technique is based not only on selected cross-sections of the tunnel contour but also on the description of the morphology of the tunnel contour surface. The case study concerns measurements of the “Mały Luboń” tunnel niche, located in Naprawa, Poland. The TCI values for three blasting rounds were determined in accordance with Kim and Bruland's guidelines and were compared to TCI values determined with the proposed TLS technique. On a basis of this comparison, it can be concluded that the results obtained with the TLS technique are more reliable and representative for description of the contour quality of the entire blasting round than results obtained with the laser profiling technique.

Pulse shape effects in high-field Bethe–Heitler pair production

Electron–positron pair production via the nonlinear Bethe–Heitler effect in the combined fields of a bare nucleus and a high-intensity laser pulse is studied theoretically. The calculations are performed within the framework of strong-field quantum electrodynamics using a flat-top laser profile with raising and falling edges. This way, the dependence of the pair production process on the precise shape of the laser field is analyzed. Our approach allows us, in particular, to follow the evolution of the created particles’ energy spectra from ultra-short few-cycle pulses to the monochromatic infinite pulse-train limit. We show how the various portions of the pulse influence these spectra and determine conditions for which the outcome from a laser pulse closely resembles the predictions from monochromatic theory.

Application of mechanistic force models to features of arbitrary geometry at low material removal rate

This paper presents a workpiece discretization method to apply existing cutting force models to predict the forces generated during low material removal rate robotic machining operations of features with arbitrary geometry. Two machining operations along a straight edge which are modelled using this feature discretization method are shown, a chamfer pass on a sharp corner and the removal of a trapezoidal cross section. The workpiece features are measured using a high-resolution laser profile scanner to obtain the volume of the features to be removed. The identified features are discretized into rectangular sections such that the cutting force models can be applied to predict the cutting forces. A linear and an exponential mechanistic model which relate tool immersion and feed rate to the cutting force are applied to the scanned workpiece features. The linear and nonlinear models show good agreement with the measured data, with the exception that the linear model occasionally over predicts the forces depending on the radial depth of cut.

Epitaxial growth of a single-crystal nickel-based superalloy during laser melting with high-power flat-top laser

Laser-induced epitaxial growth is a prevailing technique in repair of single crystal (SX) Ni-based superalloy components. However, due to the non-uniform energy distribution of typical Gaussian laser energy profile, the nucleation and growth of stray grains are often difficult to control. In the present work, a strategy of using high-power (6 KW) flat-top laser profile is adopted to control the crystalline texture of laser melted SX Ni-based superalloy. The effect of laser exposure time on the epitaxial growth is investigated and the underlying mechanism is revealed by both experimental and finite element analysis approaches. The results show that by applying a high-power flat-top laser beam, the melting pool morphology can be effectively regulated to achieve a planar liquid/solid boundary. A longer exposure time leads to a higher G/V ratio, which in turn suppresses the deflection of grain growth within the melting pool. The computed local solidification characteristics (G/V ratio and cooling rate) reveal that favorable conditions for epitaxial growth along build direction can be achieved with the proposed strategy.

Optical profile: A key determinant of antibacterial efficacy of photodynamic therapy in dentistry

BackgroundPeriodontal disease effects 20–50% of the population worldwide, posing a global health challenge. It has been reported to be more prevalent among adults. Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) is an important organism associated with localized juvenile periodontitis. Photodynamic therapy (PDT) has been widely utilized for the treatment of periodontal disease; however, the effect of laser (light) profile on the antibacterial efficacy of PDT remains to be established. The quantitative measurement of laser profile is required to confirm the in vitro efficacy of PDT. AimIn the present study, a low cost PDT system comprising of six copper tube waveguides (CTW) was developed to provide more uniform irradiation of the culture plate. MethodsThe antibacterial effect of PDT, in combination with 200 μg/mL methylene blue (MB) as photosensitizer and 60 sec of irradiation, was studied on A. actinomycetemcomitans and Streptococcus mutans (S. mutans). In the present case, 660 nm laser guided with unpolished CTW, polished CTW, and optical fiber waveguide (OFW) provided radiant exposure of 0.86, 1.38, and 1.36 J/cm2, respectively, for a 24‐well culture plate. ResultsThe designed PDT system provided antimicrobial efficacy of 98% and 91% for A. actinomycetemcomitans and S. mutans, respectively, which was significantly higher as compared to OFW guided PDT. ConclusionThe results of the study highlighted the importance of laser profile as a key parameter that determines the survival rate of bacteria at the edge of the culture plate. Thus, the dose of PDT at the margin of optical profile is important for antibacterial activity for in vitro evaluation.

Surface absorption illumination in a 2D thermoelastic semi-infinite medium under modified Green and Lindsay model

In this study, the modified Green and Lindsay model is utilized to discuss the effects of heating caused by surface absorption of laser radiation in a two-dimensional thermoelastic half-space. The temporal profile of the pulsed laser is taken as a non-Gaussian and the spatial one is a Gaussian. The medium surface is taken to be traction free. The integral transform method is utilized to obtain the general solution by applying the two transformations Hankel and Laplace, in which the inverse of Laplace is performed numerically. The Silicon material is considered as an example to verify the consistency of the obtained results of the new model.

Electron Acceleration by a radially polarised cosh-Gaussian laser beam in vacuum

In this paper, a radially polarised cosh-Gaussian laser beam (CGLB) is used to study the electron acceleration produced in vacuum. A highly energetic electron beam can be achieved by a CGLB, even with comparatively low-powered lasers. The properties of a CGLB cause it to focus earlier, over a shorter duration than a Gaussian laser beam, which makes it suitable for obtaining high energies over small durations. It is found that the energy gained by the electrons strongly depends upon the decentering parameter of the laser profile. It is also observed that for a fixed value of energy gain, if the decentering parameter is increased, then the intensity of the laser field decreases. The dependence of the energy gained by electrons on the laser intensity and the laser-spot size is also studied.

Focal laser stimulation of fly nociceptors activates distinct axonal and dendritic Ca2+ signals

Drosophila class IV neurons are polymodal nociceptors that detect noxious mechanical, thermal, optical, and chemical stimuli. Escape behaviors in response to attacks by parasitoid wasps are dependent on class IV cells, whose highly branched dendritic arbors form a fine meshwork that is thought to enable detection of the wasp’s needle-like ovipositor barb. To understand how mechanical stimuli trigger cellular responses, we used a focused 405-nm laser to create highly localized lesions to probe the precise position needed to evoke responses. By imaging calcium signals in dendrites, axons, and soma in response to stimuli of varying positions, intensities, and spatial profiles, we discovered that there are two distinct nociceptive pathways. Direct stimulation to dendrites (the contact pathway) produces calcium responses in axons, dendrites, and the cell body, whereas stimulation adjacent to the dendrite (the noncontact pathway) produces calcium responses in the axons only. We interpret the noncontact pathway as damage to adjacent cells releasing diffusible molecules that act on the dendrites. Axonal responses have higher sensitivities and shorter latencies. In contrast, dendritic responses have lower sensitivities and longer latencies. Stimulation of finer, distal dendrites leads to smaller responses than stimulation of coarser, proximal dendrites, as expected if the contact response depends on the geometric overlap of the laser profile and the dendrite diameter. Because the axon signals to the central nervous system to trigger escape behaviors, we propose that the density of the dendritic meshwork is high not only to enable direct contact with the ovipositor but also to enable neuronal activation via diffusing signals from damaged surrounding cells. Dendritic contact evokes responses throughout the dendritic arbor, even to regions distant and distal from the stimulus. These dendrite-wide calcium signals may facilitate hyperalgesia or cellular morphological changes after dendritic damage.

RADLER – A UNICYCLE AS A LOW-COST RADIAL LASER SCANNER

Abstract. In recent years a wide range of 3D multi sensor systems for various applications has been proposed. Each of them has its own benefits and limitations. This paper proposes a modified unicycle with a 2D laser profiler attached to the wheel axle, thus creating a radial 3D scanning pattern. This novel low-cost device combines the advantages of wheeled scanning equipment with those of wearable or hand-held devices. After presenting the hardware setup and the sensor integration, the results are evaluated using four test scenarios and a terrestrial laser scanner for comparison.

A portable measurement system for pavement surface macrotexture – a case study in China

ABSTRACT This study proposes a portable measurement system (PS) for pavement surface macrotexture, which improves the current detection technology and provides the necessary support for maintenance and evaluation works on urban roads, newly built roads, parking, footpath, tunnels, bicycle lanes, and short distance roads. The system can obtain the elevation values through a high precision laser sensor and a data acquisition card. Next, the outliers of natural elevation values are screened and interpolated by a statistical test method, and then the corrected data are filtered by an improved Kalman filter algorithm. Finally, the mean profile depth (MPD) is calculated based on the standard ASTM E1845-15. The replication experiments, the correlation experiments with sand patch test (SPT), and the comparative experiment with vehicle laser profiler (VLP) are carried out on 20 test sections. The results show that the variation coefficients of PS are less than 5%, the correlation indexes with SPT are more than 0.928, the mean square errors and the mean absolute percentage errors of PS are less than 0.0032 and 4.98%, respectively. Meanwhile, the conversion models of MPD with mean texture depth (MTD) are established to realise that the direct estimation of MTD data utilising MPD data for different pavement types.

Comparison of skid resistance of EAC pavement with different maximum aggregate grain size

ABSTRACT The paper presents a comparison of friction coefficients and MPD (Mean Profile Depth) parameters of EAC (Exposed Aggregate Concrete) pavements with a maximum aggregate size of 8, 11 and 14 mm. In order to obtain for all tested EAC pavements the same conditions that simulate the phenomenon of polishing, tests were performed using a FAP (Friction After Polishing) machine in laboratory conditions. Macrotexture measurements were made on the surface of each sample using an Elatexure laser profile. In addition, three types of coarse aggregates were selected based on their resistance to polishing, which was determined on the basis of PSV (Polished Stone Value). Based on ANOVA, a significant influence of maximum aggregate size on both the friction coefficient and the MPD parameter was demonstrated. Along with the increase in the aggregate maximum grain size in EAC, the increase in MPD value was recorded. Despite of this fact, no effect of resistance to the polishing of aggregates with PSV from 48 to 52 on skid resistance was demonstrated. However, the decision to apply individual solutions should take into account road classification in the road network system, traffic volume and speed limits.

A model of bead size based on the dynamic response of CMT-based wire and arc additive manufacturing process parameters

PurposeThis paper aims at fabricating large metallic components with high deposition rates, low equipment costs through wire and wire and arc additive manufacturing (WAAM) method, in order to achieve the morphology and mechanical properties of manufacturing process, a bead morphology prediction model with high precision for ideal deposition of every pass was established.Design/methodology/approachThe dynamic response of the process parameters on the bead width and bead height of cold metal transfer (CMT)-based AM was analyzed. A laser profile scanner was used to continuously capture the morphology variation. A prediction model of the deposition bead morphology was established using response surface optimization. Moreover, the validity of the model was examined using 15 groups of quadratic regression analyzes.FindingsThe relative errors of the predicted bead width and height were all less than 5% compared with the experimental measurements. The model was then preliminarily used with necessary modifications, such as further considering the interlayer process parameters, to guide the fabrication of complex three-dimensional components.Originality/valueThe morphology prediction of WAAMed bead is a critical issue. Most research has focused on the formability and defects in CMT-based WAAM and little research on the effect of process parameters on the morphology of the deposited layer in CMT-based WAAM has been conducted. To test the sensitivities of the processing parameters to bead size, the dynamic response of key parameters was investigated. A regression model was established to guide the process parameter optimization for subsequent multi-layer or component deposition.

Hermite-cosh-Gaussian laser-induced third harmonic generation in plasma

Present work focuses on Hermite-cosh-Gaussian (HchG) laser-induced third harmonic generation (THG) in plasma on account of self-focusing. HchG laser beam gets self-focused due to ponderomotive force while propagating in plasma. Interaction of intense laser pulse results ponderomotive force on electrons and induce density perturbation that produces density oscillations at second harmonic frequency. Induced density perturbation beats with quiver velocity of electrons at laser frequency to produce a third harmonic nonlinear current. Application of wiggler magnetic field satisfies the phase matching condition which results resonant THG. Significant enhancement in the efficiency of THG is observed by using HchG laser profile for mode index m = 2. Small variation in decentered parameter also affects the THG efficiency which shows the sensitivity of decentered parameter.

Multi-dimensional kinetic simulations of laser radiation absorption and electron acceleration in inhomogeneous underdense plasma

The sub-relativistic laser beam interaction with an underdense plasma is investigated via two-dimensional (2D) numerical simulations with respect to the laser polarization direction. Different parametric instabilities dominate the interaction depending on the propagation direction of the daughter waves in the simulation plane with respect to the laser field polarization and laser propagation direction. In the plane containing the laser electric field (p-polarization) the interaction is dominated by the two-plasmon decay instability and the beating of large amplitude electron plasma waves produces periodic ion density perturbations suppressing stimulated Raman scattering in the quarter critical density zone. A stronger absorption and heating of hot electrons is observed in the case where laser polarization is perpendicular to the simulation plane (s-polarization). Furthermore, by comparing a plane laser wave with a narrow beamlet, the effect of the initial transverse laser profile is proven to play an important role in exciting the filamentation instability, which competes with stimulated Brillouin scattering and affects the laser absorption and hot electron generation. A dedicated three-dimensional simulation indicates that a 2D simulation with p-polarization produces a more reliable results while the case of s-polarization overestimates the laser absorption and hot electron generation.

Integrating Pavement Sensing Data for Pavement Condition Evaluation.

Highway pavements are usually monitored in terms of their surface performance assessment, since the major cause that triggers maintenance is reduced pavement serviceability due to surface distresses, excessive pavement unevenness and/or texture loss. A common way to detect pavement surface condition is by the use of vehicle-mounted laser sensors that can rapidly scan huge roadway networks at traffic speeds without the need for traffic interventions. However, excessive roughness might sometimes indicate structural issues within one or more pavement layers or even issues within the pavement foundation support. The stand-alone use of laser profilers cannot provide the related agencies with information on what leads to roughness issues. Contrariwise, the integration of multiple non-destructive data leads to a more representative assessment of pavement condition and enables a more rational pavement management and decision-making. This research deals with an integration approach that primarily combines pavement sensing profile and deflectometric data and further evaluates indications of increased pavement roughness. In particular, data including Falling Weight Deflectometer (FWD) and Road Surface Profiler (RSP) measurements are used in conjunction with additional geophysical inspection data from Ground Penetrating Radar (GPR). Based on pavement response modelling, a promising potential is shown that could proactively assist the related agencies in the framework of transport infrastructure health monitoring.

Characterization of a chromatic confocal displacement sensor integrated with an optical laser head.

In this paper, the results of experimental characterization of an optical system consisting of a chromatic confocal displacement sensor integrated with an optical laser head are presented. As a result of integration, the part of the optical path of the displacement sensor was combined with the optical path of the laser beam. Consequently, a working distance of 250 mm for the optical system was achieved. The main aim of the characterization was to determine the calibration curve, as well as the application parameters of the system. The methodology for spectral data processing with particular emphasis on the effectiveness of various extraction algorithms is presented. The Lorentzian fitting was considered as the optimal algorithm for the optical system. Consequently, a large measuring range of 10 mm was obtained with perfect linear tendency of the calibration curve. The optical system was characterized by high accuracy equal to ±0.11% of the measuring range, as well as 1 µm resolution. Moreover, the functionality of the system was verified on materials commonly used in laser processing and additive manufacturing. Finally, the system was validated through a comparative measurement with a laser profiler.

Our experience in the treatment of hemangioma with intense pulsed light laser: A 10 year study in Albania.

Laser treatment brought an innovation in the treatment of hemangiomas and vascular anomalies. The range of superficial vascular lesions that can be treated with laser continues to expand. In our country laser device date relatively late, since then these technologies have facilitated the treatment of many skin condition. The goal of laser therapy is to maximize vascular destruction while minimizing injury to surrounding healthy epidermis and dermal tissues. We present our experience with IPL as a first line therapy in the treatment of superficial hemangiomas. After institutional review, board approval we analyzed the medical records of 202 patients diagnosed with hemangioma and treated with the IPL laser during January 2009 to January 2019. The performed procedure consists of using impulses of light with wave length that varies from 590 to 595 nm, duration 1.5 ms, and fluency by 11 to 12 J/cm2 . For each patient, four PDL sessions have been performed. We aim to evidence the efficacy and the good safety profile of (IPL) laser but with small adverse events that this treatment represent. The importance of proper patient selection, use of appropriate equipment settings, skin cooling mechanisms, and other safety measures minimize the occurrence of adverse events due to IPL treatment.

Laser pointing and characterization parameter determination methods based on laser profile arrays of ICESat/GALS.

Satellite laser altimeter data are used for polar ice sheet elevation mapping, vegetation mapping, etc. Data quality mainly depends on complex relationships among several factors in the path of laser transmission and on illuminated surfaces, including clouds, atmospheric aerosol, satellite pointing, laser energy, topography, footprint size, shape and orientation. The precise pointing of the transmitted laser pulse is critical for improving the horizontal accuracy of the footprint on the ground. Thus, we extracted the centroid of the laser profile array (LPA) image of ICESat/GLAS by 1/e2 maximum energy distribution method. The results show that the accuracy of extraction of the LPA's centroid improved by 0.3 pixel, and the relative positioning accuracy improved by 0.11 pixel. The fast Fourier transform and Fourier series fitting of the LPA centroid has been implemented to detect the periodic change and analyze the model regularity. The results show that the centroid of the LPA undergoes four periodic changes: 1.83 × 10-4, 3.36 × 10-4, 5.19 × 10-4, and 6.71 × 10-4Hz. The correlation of fit is a good indicator (R2=0.86) and accurate up to 0.4 arcsec (approximately 0.13 pixel). Finally, we extract and estimate the LPA characteristic parameters (eccentricity, orientation, total intensity, and major axis) in different campaigns. We observe that the results obtained by the 1/e2maximum energy distribution are only approximate.

Shape-Based Alignment of the Scanned Objects Concerning Their Asymmetric Aspects.

We introduce an integrated method for processing depth maps measured by a laser profile sensor. It serves for the recognition and alignment of an object given by a single example. Firstly, we look for potential object contours, mainly using the Retinex filter. Then, we select the actual object boundary via shape comparison based on Triangle Area Representation (TAR). We overcome the limitations of the TAR method by extension of its shape descriptor. That is helpful mainly for objects with symmetric shapes but other asymmetric aspects like squares with asymmetric holes. Finally, we use point-to-point pairing, provided by the extended TAR method, to calculate the 3D rigid affine transform that aligns the scanned object to the given example position. For the transform calculation, we design an algorithm that overcomes the Kabsch point-to-point algorithm’s accuracy and accommodates it for a precise contour-to-contour alignment. In this way, we have implemented a pipeline with features convenient for industrial use, namely production inspection.