Laser Exposure Time Research Articles

Laser-induced hyperthermia of nanoshell mediated vascularized tissue – A numerical study

Laser-induced hyperthermia treatment of tumor in a 2-D axisymmetric tissue embedded with moderate size (100–150µm) blood vessels is studied. Laser absorption is enhanced by embedding gold–silica nanoshells in the tumor. Heat transfer in the tissue is modeled using Weinbaum–Jiji bioheat transfer equation. With laser irradiation, the volumetric radiation is accounted in the governing bioheat equation. Radiative information needed in the bioheat equation is calculated using the discrete ordinate method, and the coupled bioheat-radiation equation is solved using the finite volume method. Effects of power density, laser exposure time, beam radius, diameter of blood vessel and volume fractions of nanoshells on temperature spread in the tissue are analyzed.

Simulation and Study of Temperature Distribution in Living Biological Tissues under Laser Irradiation.

With the rapid increase in use of lasers in medical treatments, it is important to understand the mechanisms of heat transfer in biological tissues in order to minimize damage to the tissues resulting from extra heat applied. The aim of this study is to investigate the temperature distribution in living biological tissues when laser irradiation is used in a treatment. In this work a model was suggested to study the impact of several parameters such as (laser power, exposure time, laser spot size) on the temperature distribution within skin tissues when subjected to a laser source. A three-dimensional finite element thermal model of biological tissues was developed using bio-heat equation to describe heat transfer in living tissues. Temperature distribution within skin tissues subjected to laser heating is calculated in details using the Finite element method and a suggested model; the results are presented in figures and tables showing the effects of Laser spot size, power and exposure time on temperature distribution within treated tissue. the results presented in this work are expected to be useful in optimizing Laser spot size, power and exposure time for a variety of laser applications medicine and surgery.

Eye injury model by diffuse low dose 532nm laser in rats and the changes of electroretinogram

Objective To establish effective,controllable,simple and well repeatable rat eye model injured by diffuse low dose 532 nm laser.Methods The animal models in rats were made by selfmade laser device and apparatus.These rats were divided into six groups according to their exposure time:instant,1 d,3 d,5 d,7 d and 14 d.After exposure,the rats were examined by direct ophthalmoscopy,fundus photography,fundus flurescein angiography and electroretinogram.Results The rat eye model injured by diffuse low dose 532 nm laser was successfully established.The results of direct ophthalmoscopy,fundus photography,fundus flurescein angiography in these models were normal.As shown by electroretinogram,with laser exposure time expending,0.01 rod response of b wave amplitude decreases,0.3 max response of a and b waves amplitude decreased,0.3 cone response of a and b waves incubation period extended and amplitude decreased significantly (P ＜ 0.05).There was no significant difference in oscillatorypotentials(P ＞ 0.05).Conclusion The rat eye model injured by low dose laser is effective,controllable,simple and well repeatable.With the laser exposure time expending,the retinal electrophysiological activity decreases.It shows the visual electrophysiological examination is important for evaluation of eye injury due to low dose laser.The platean period is 7 d to 14 d after laser exposure. Key words: Laser, 532nm; Dose, low; Model, animal, rat; Injury, ocular; Examination,electrophysiology, visual

Abstract 501: Noninvasive Photodynamic Therapy of Murine Atherosclerosis Using Macrophage-Targeted Nanoparticles

Objectives: Cerebrovascular disease leading to stroke remains a leading cause of death and disability worldwide. Photodynamic therapy (PDT) of atherosclerotic plaque macrophages may be a promising approach to stabilize rupture-prone carotid lesions, but a noninvasive PDT method for carotid atherosclerosis is lacking. Here we developed a near-infrared (NIR) absorbing macrophage-targeted photosensitizing nanoparticle to determine whether plaque macrophages can be successfully ablated using noninvasive PDT. Methods: CLIO-CyAm7-Chlorin is a dextran-based nanoparticle that contains a NIR photosensitizer (Chlorin, abs 650nm) for PDT, and a discrete NIR fluorochrome (CyAm7, ex/em 750/767nm) for fluorescence imaging of nanoparticle distribution. Noninvasive PDT optimization was performed in vivo via a PDT ablation study of hepatic macrophages in C57BL6 mice (n=65). Varying doses, exposure times, and laser power were explored. A separate group of ApoE-/- mice (n=16, 8wk HCD) injected with CLIO-Chlorin-CyAm7 or control CLIO-CyAm7 (10mgFe/kg) received noninvasive PDT of aortic root atheroma. Mice were sacrificed 1 day post-PDT for histology. Computational simulations of noninvasive PDT for human plaques were studied at multiple PDT wavelengths and light fluence. Results: Noninvasive PDT optimization showed that increasing doses of CLIO-CyAm7-Chlorin and laser exposure time had strong linear correlations with increasing liver injury (r2=0.88 and 0.65, respectively). Mice injected with control CLIO-CyAm7 showed no damage of the liver by tunel or H&E, independent of dose or time of PDT. In ApoE-/- mice, CLIO-CyAm7-Chlorin and CLIO-CyAm7 localized to inflamed aortic root plaques, and was confirmed to be macrophage localized on fluorescence imaging. CLIO-CyAm7-Chlorin/PDT showed a 6-fold increase in tunel (+) cells in aortic root plaques compared to control CLIO-CyAm7/PDT treated animals (p<0.01). Computational simulations revealed that further NIR-shifting of the photosensitizer would enable noninvasive PDT up to 1-2 cm deep, potentially enabling noninvasive PDT of human carotid plaques. Conclusions: CLIO-CyAm7-Chlorin is a multifunctional NIR nanoparticle that allows noninvasive macrophage-targeted PDT of atherosclerosis.

Nd:Yag laser irradiation of single lap joints made by polyethylene and polyethylene doped by carbon nanomaterials

Thermoplastic polyethylene can be welded by the transmission laser welding technique (TTLW) that exhibits some process related benefits with respect other conventional joining methods. This justifies its large use in wide fields, from the automotive to medical or domestic appliances. In this research, we studied single lap joints made by polyethylene pure and filled with carbon nanomaterials (0.2% in weight) to make the polymer laser absorbent. The joints were irradiated by a Nd:YAG laser operating at 1064 nm (first harmonic) with an intensity of 107 W/cm2 and 1 ÷ 30Hz, a maximum pulse energy of 300mJ and a laser spot of ≈ 1 cm2 (no focusing lens were employed). The joints were characterized by morphological analysis, mechanical shear tests and calorimetric analysis. The results suggested that the laser exposition time must be opportunely balanced in order to avoid a poor adhesion between the polymer sheets and to realized efficient joints. In particular the mechanical test showed that the laser exposition time of 40 seconds is the best conditions to obtain the highest shear strength of the joints of 140 N. After too prolonged laser exposure times, degrading phenomena starts.

Fabrication of a three-dimensional tissue model microarray using laser foaming of a gas-impregnated biodegradable polymer

A microarray containing three-dimensional (3D) tissue models is a promising substitute for the two-dimensional (2D) cell-based microarrays currently available for high throughput, tissue-based biomedical assays. A cell culture microenvironment similar to in vivo conditions could be achieved with biodegradable porous scaffolds. In this study, a laser foaming technique is developed to create an array of micro-scale 3D porous scaffolds. The effects of major process parameters and the morphology of the resulting porous structure were investigated. For comparison, cell culture studies were conducted with both foamed and unfoamed samples using T98G cells. The results show that by laser foaming gas-impregnated polylactic acid it is possible to generate an array of inverse cone shaped wells with porous walls. The size of the foamed region can be controlled with laser power and exposure time, while the pore size of the scaffold can be manipulated with the saturation pressure. T98G cells grow well in the foamed scaffolds, forming clusters that have not been observed in 2D cell cultures. Cells are more viable in the 3D scaffolds than in the 2D cell culture cases. The 3D porous microarray could be used for parallel studies of drug toxicity, guided stem cell differentiation, and DNA binding profiles.

Engineering of Bi2Se3nanowires by laser cutting

We present a method to control the length and diameter of Bi 2 Se 3 nanowires through laser-cutting. Nanowires of the topologically insulating and thermoelectric material Bi 2 Se 3 were grown using the vapor-liquid-solid method, and cut using a 532-nm-laser operating at a minimum power of 1 μ W. The cutting process can be controlled through laser intensity and exposure time, and is based upon evaporation of Se from the nanowires. This method has many applications from pure research to device engineering.

Efficient Intracellular Delivery of Molecules with High Cell Viability Using Nanosecond-Pulsed Laser-Activated Carbon Nanoparticles

Conventional physical and chemical methods that efficiently deliver molecules into cells are often associated with low cell viability. In this study, we evaluated the cellular effects of carbon nanoparticles believed to emit photoacoustic waves due to nanosecond-pulse laser activation to test the hypothesis that this method could achieve efficient intracellular delivery while maintaining high cell viability. Suspensions of DU145 human prostate carcinoma cells, carbon black (CB) nanoparticles, and calcein were exposed to 5–9 ns long laser pulses of near-infrared (1064 nm wavelength) light and then analyzed by flow cytometry for intracellular uptake of calcein and cell viability by propidium iodide staining. We found that intracellular uptake increased and in some cases saturated at high levels with only small losses in cell viability as a result of increasing laser fluence, laser exposure time, and as a unifying parameter, the total laser energy. Changing interpulse spacing between 0.1 and 10 s intervals showed no significant change in bioeffects, suggesting that the effects of each pulse were independent when spaced by at least 0.1 s intervals. Pretreatment of CB nanoparticles to intense laser exposure followed by mixing with cells also had no significant effect on uptake or viability. Similar uptake and viability were seen when CB nanoparticles were substituted with India ink, when DU145 cells were substituted with H9c2 rat cardiomyoblast cells, and when calcein was substituted with FITC-dextran. The best laser exposure conditions tested led to 88% of cells with intracellular uptake and close to 100% viability, indicating that nanosecond-pulse laser-activated carbon nanoparticles can achieve efficient intracellular delivery while maintaining high cell viability.

Laser-assisted fragmentation of Al particles suspended in liquid

Laser-assisted fragmentation of Al micro- and nano-particles in liquid is studied both experimentally and theoretically. Modeling of the evolution of size distribution function of particles is performed on the basis of numerical solution of kinetic equation for distribution function which takes into account the ablation and splitting of particles into fragments of different sizes. It is assumed that depending on the size of particles, the fragmentation scenario may vary from monoatomic evaporation to detachment of relatively large fragments. The first mechanism of fragmentation is typical for nanoparticles while the second one is characteristic for large (micrometer-sized) particles. Laser-assisted fragmentation of Al micro-particles suspended in liquid ethanol to Al nanoparticles is experimentally studied using a Nd:YAG laser with pulse duration of 10ps and repetition rate of 300kHz. The evolution of the size distribution function with laser exposure time is monitored and compared to modeling results.

The short-term efficacy of subthreshold Micropulse yellow (577-nm) laser photocoagulation for diabetic macular edema.

PurposeThis pilot study aimed to evaluate the efficacy and safety of subthreshold micropulse yellow (577-nm) laser photocoagulation (SMYLP) in the treatment of diabetic macular edema (DME).MethodsWe reviewed 14 eyes of 12 patients with DME who underwent SMYLP with a 15% duty cycle at an energy level immediately below that of the test burn. The laser exposure time was 20 ms and the spot diameter was 100 µm. Laser pulses were administered in a confluent, repetitive manner with a 3 × 3 pattern mode.ResultsThe mean follow-up time was 7.9 ± 1.6 months. The baseline-corrected visual acuity was 0.51 ± 0.42 logarithm of the minimum angle of resolution (logMAR), which was improved to 0.40 ± 0.35 logMAR (p = 0.025) at the final follow-up. The central macular thickness at baseline was 385.0 ± 111.0 µm; this value changed to 327.0 ± 87.7 µm (p = 0.055) at the final follow-up.ConclusionsSMYLP showed short-term efficacy in the treatment of DME and did not result in retinal damage. However, prospective, comparative studies are needed to better evaluate the efficacy and safety of this treatment.

High-Precision Surface Inspection: Uncertainty Evaluation within an Accuracy Range of 15μm with Triangulation-based Laser Line Scanners

AbstractTriangulation-based range sensors, e.g. laser line scanners, are used for high-precision geometrical acquisition of free-form surfaces, for reverse engineering tasks or quality management. In contrast to classical tactile measuring devices, these scanners generate a great amount of 3D-points in a short period of time and enable the inspection of soft materials. However, for accurate measurements, a number of aspects have to be considered to minimize measurement uncertainties. This study outlines possible sources of uncertainties during the measurement process regarding the scanner warm-up, the impact of laser power and exposure time as well as scanner’s reaction to areas of discontinuity, e.g. edges. All experiments were performed using a fixed scanner position to avoid effects resulting from imaging geometry. The results show a significant dependence of measurement accuracy on the correct adaption of exposure time as a function of surface reflectivity and laser power. Additionally, it is illustrated that surface structure as well as edges can cause significant systematic uncertainties.

Nanocatalyst support of laser-induced photocatalytic degradation of MTBE

This study was undertaken to develop a methodology suitable for the direct removal and degradation of methyl tertiary butyl ether (MTBE) in water using different nano-catalysts supported laser based photo-oxidation process. For this purpose, nano-structured WO3 catalyst was synthesized in our laboratory and its photocatalytic activity for the demineralization of MTBE in water was compared with different catalysts such as ZnO, TiO2, Fe2O3 and NiO using 355 nm laser radiations generated by the third harmonic of Nd: YAG laser. The effect of laser irradiation time, amount of catalysts and pH were also investigated for the optimization of MTBE removal process. For 60 min of laser exposure time, the overall percentage of MTBE degradation was found to be 93%, 89%, 82%, 80% and 71% for WO3, ZnO, Fe2O3, NiO and TiO2, respectively. In addition the photonic efficiencies of different nano-structured catalysts toward degradation of MTBE were estimated, and they were found to follow the trend of WO3 > ZnO > Fe2O3 > NiO > TiO2.

Characterization of “Bulk Lithography” Process for Fabrication of Three-Dimensional Microstructures

Various ways of fabricating a three-dimensional (3D) component in a single-layer exposure using spatial variation of exposure dose have been presented in the literature. While some of them are based on dynamic mask process, more recently, a process based on varying intensity of a scanning Gaussian laser beam termed as “bulk lithography” has been proposed. In bulk lithography, the entire varying depth 3D microstructure gets fabricated because of spatial variation of intensity of laser imposed at every point in single layer scan. For the bulk lithography process, this paper first presents experimental characterization of unconstrained depth photopolymerization of resin upon exposure to Gaussian laser beam. Experimental characterization carried out for two resins systems: namely 1,6 hexane diol-diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA), over relatively wider range of Ar+ laser exposure dose and time, show behavior well beyond Beer–Lambert law. A unified empirical model is proposed to represent the nondimensional depth variation with respect to the time and energy of exposure for both resins. Finally, using these models, successful fabrication of several microstructures including micro-Fresnel lens, textured curved surface, otherwise difficult or impossible to fabricate, is demonstrated. Several advantages of the bulk lithography as compared to other similar processes in the literature are highlighted.

Low-velocity impact performance of lattice structure core based sandwich panels

This paper outlines the findings of a study on a range of stainless steel and titanium alloy lattice structures manufactured using the selective laser melting technique. The effect of varying key manufacturing parameters on the properties of lattice strands was studied through a series of single-filament tensile tests. The resulting failure mechanisms were investigated using a scanning electron microscope. The resulting observations have shown that the properties of these lattice strands are determined by the laser energy during the manufacturing process, which in turn is controlled by the laser power and laser exposure time. The quasi-static and low-velocity penetration behaviour of lattice core-based sandwich panels has been examined, and an aluminium foam and an aluminium honeycomb were chosen to benchmark their performance. The impact resistance of the lattice core-based sandwich structures were shown to be dependent on both the manufacturing parameters and lattice unit-cell geometry of the lattice structure. The impact resistances were improved by increasing manufacturing laser energy and lattice core density. A series of drop-weight tests at velocities up to 6 m/s have shown that the penetration behaviour of the titanium alloy lattice cores and the aluminium honeycomb cores is similar.

Optimization in interstitial plasmonic photothermal therapy for treatment planning

Gold nanorods have the potential to enhance the treatment efficacy of interstitial photothermal therapy. In order to enhance both the potential efficiency and the safety of such procedures, treatment planning on laser power density, nanoparticle concentration, and exposure time has turned out to be useful in predicting the thermal damage and optimizing treatment outcome. To the best of our knowledge, there is no previous report on the optimization of interstitial plasmonic photothermal therapy (PPTT) for all these free parameters simultaneously. The authors propose to develop a suitable optimization algorithm for interstitial PPTT to optimize these parameters and achieve complete damage to spherical tumors of different sizes with a damage margin width of 1 mm from the tumor boundary embedded deep inside a normal tissue model. In a numerical tissue model, the standard Pennes bioheat equation and the first-order thermal-chemical rate equation were used to model the temperature and thermal damage distributions, respectively, in spherical tumors that were embedded deep inside a normal tissue and incubated with nanorods. The concentration of nanorods in the normal tissue was set to be about one quarter of that in the tumor. Thermal damage due to varying concentrations of nanorods, laser power density, and exposure time was computed for a series of tumor radii including 2, 3, 4, and 5 mm. An optimization algorithm was developed to determine the optimum laser power density, nanorod concentration, and exposure time for the treatment of such spherical tumors. In this algorithm, a novel objective function was created to enable the optimization of multiple key parameters, including nanoparticle concentration, power density, and exposure time, simultaneously to achieve not only the complete thermal damage to the entire tumor but also the collateral damage to the surrounding normal tissue with a margin width of 1 mm from the tumor boundary. Different weights were assigned sequentially to each free parameter according to the relative importance of the parameters. A thermal damage value of one calculated by Arrhenius damage law, which is more accurate than a threshold temperature typically used for characterizing thermal damage, was used to indicate effective treatment. The simulation results show that there is a steady increase in the overall temperature as the nanorod concentration increases; however, the uniformity of the temperature distribution changes significantly which in turn affects the thermal damage. Optimization results show that any slight decrease in one free parameter can be compensated by the increase in other free parameters, in which the complete thermal damage of the tumor and the collateral damage to normal tissue with a margin width of 1 mm can be always achieved. This implies the importance of optimization in interstitial PPTT. The proposed method can optimize laser power density, nanoparticle concentration, and exposure time simultaneously with different weights in interstitial PPTT planning for deep seated tumors. It provides flexibility for a clinician to make appropriate planning for individual patients according to their special needs.

Femto‐Second Laser‐Based Free Writing of 3D Protein Microstructures and Micropatterns with Sub‐Micrometer Features: A Study on Voxels, Porosity, and Cytocompatibility

Femto‐second laser‐based free‐writing of complex protein microstructures and micropatterns, with sub‐micrometer features and controllability over voxel dimension, morphology, and porosity, is reported. Protein voxels including lines, spots, and micropillars are fabricated. Laser power, exposure time, z‐position, protein and photosensitizer concentrations, but not scanning speed, are important controlling parameters. A lateral fabrication resolution of ≈200 nm is demonstrated in 2D line voxels. 3D spot voxels are ellipsoids with 400 nm lateral and 1.5 μm axial dimensions. An ascending z‐stack scanning method to verify the theoretical axial optical resolution, delineate and enhance the axial fabrication resolution of 3D structures, including square prism and cylinder micropillars, is also reported. The micropillar array presents a simple “write‐and‐seed” and table platform for cell niche studies. Fibroblasts attach to, grow on, and express adhesion to molecules on micropillar arrays without the need of matrix coating. They exhibit a more “3D” morphology comparing with that in 2D monolayer cultures and physiological functions such as matrix deposition. This work presents an important milestone in engineering complex protein microstructures and micropatterns with sub‐micrometer topological features to mimic the native matrix niche for cell‐matrix interaction studies.

Chemically assisted femtosecond laser machining for applications in LiNbO3 and LiTaO3

We introduce and optimize a fabrication procedure that employs both femtosecond laser machining and hydrofluoric acid etching for cutting holes or voids in slabs of lithium niobate and lithium tantalate. The fabricated structures have 3 μm lateral resolution, a lateral extent of at least several millimeters, and cut depths of up to 100 μm. Excellent surface quality is achieved by initially protecting the optical surface with a sacrificial silicon dioxide layer that is later removed during chemical etching. To optimize cut quality and machining speed, we explored various laser-machining parameters, including laser polarization, repetition rate, pulse duration, pulse energy, exposure time, and focusing, as well as scanning, protective coating, and etching procedures. The resulting structures significantly broaden the capabilities of terahertz polaritonics, in which lithium niobate and lithium tantalate are used for terahertz wave generation, imaging, and control. The approach should be applicable to a wide range of materials that are difficult to process by conventional methods.

Laser Irradiation Effect on Structural and Optical Properties of CuO Thin Films Prepared by Chemical Spray Pyrolysis

substrate at temperature (635 K) by chemical spray pyrolysis technique. The films were annealed with CW diode laser (808 nm) for (1 and 3) min. X-ray diffraction (XRD) was used to study the structure of the films. The patterns showed that the films as-prepared have typical peaks of monoclinic tenorite (CuO), which confirmed by (111) and (111) diffraction peaks. The later peak disappeared with laser annealing for (1 and 3) min and (200) peak appeared. The annealing leads to increase the intensity of (111) diffraction peak. The UV-Vis spectrophotometer was used to study the optical properties of the films. The results showed that the annealing leads to increase the transmittance and decrease the absorbance. The optical energy gap (Eg) of these films is direct, and it increases with increasing the laser exposure time.

Micromagnetic investigation of all-optical switching

This Letter investigates all-optical magnetization switching from micromagnetic perspective. The influence of circularly polarized light on a magnetic sample was considered to be both directly through the inverse Faraday effect and indirectly aided by thermal induced effects by the laser beam. Dependence of all-optical switching on pulse duration, laser intensity and the magneto-optical susceptibility strength is studied. An important aspect of this investigation is the analysis of how the cooling process influences the successive switches, especially through limiting the successive writing time. • The effects of laser exposure time and laser intensity on the stability of all-optical switching are analyzed. • The correlation between times involved into all-optical magnetization reversal is established. • The influence of cooling process on successive switches is analyzed.

Role of photo-assisted tunneling in time-dependent second-harmonic generation from Si surfaces with ultrathin oxides

Optical second-harmonic generation (SHG) from Si surfaces covered with nanometer-thin SiO2 varies with the laser exposure time because of photo-injection and charge trapping. We use UV lamp excitation to decompose the effects of photo-injection and charge trapping on the time-dependence of SHG of 1.65 eV photons at the Si/SiO2 interface. We find that the time-dependence of SHG in air arises mainly from the cooperative effect of three-photon photo-injection and charge trapping by surface O2. When the oxide is ultrathin (≤1.5 nm), the time-dependence also includes a significant contribution from one and two-photon photo-assisted tunneling.