Dual-pulse Laser Research Articles

Satisfactory treatment of mucocutaneous lesions in hereditary hemorrhagic telangiectasia patients with dual pulsed dye laser and neodymium: yttrium-aluminum-garnet.

Hereditary hemorrhagic telangiectasia (HHT) is characterized by telangiectasia and larger arteriovenous malformations (AVM) in different organs. Mucocutaneous telangiectasia can bleed and cause stigmatization, but the best treatment approach has not been defined yet. The aim of the study was to evaluate the efficacy and safety of dual pulsed dye laser and neodymium: yttrium-aluminum-garnet (PDL-Nd:YAG) laser treatment for mucocutaneous telangiectasia in HHT patients. It is a retrospective case series, where clinical files of all HHT patients treated with PDL-Nd:YAG laser at our Department between December 2010 and July 2019 were reviewed. Demographic, clinical, and treatment characteristics were recorded. The severity and degree of improvement were evaluated by three blinded examiners scoring pretreatment and posttreatment pictures on a 5-point scale. Patient satisfaction and procedure pain were assessed using an ordinal scale (0-10). Forty-three treatment areas from 26 patients were analyzed. Lesions were predominantly located on the lower lip and cheeks. The median number of laser sessions per patient was 3 (interquartile range [IQR] 2-4). The median global severity score at baseline was 2 and became 0 at endpoint (p < 0.0001), with a median improvement rate of 4 (IQR 3-4). All patients reported a high degree of satisfaction (median 9) and tolerable pain (median 5). In conclusion, dual PDL-Nd: YAG laser is a convenient, safe, and effective treatment option for mucocutaneous telangiectasia in HHT patients.

Synthesis of Ag/Co nanoparticles by dual pulsed laser ablation for synergistic photothermal study

Synthesis of Ag/Co nanoparticles by dual pulsed laser ablation for synergistic photothermal study

Tungsten plasma density and temperature time analysis using 1.064 upmu m nanosecond dual-pulse laser

The information about time evolution of plasma electron temperature and density plays a fundamental role in numerous physics-related sciences. For CF DP-LIBS (calibration-free double-pulse laser-induced breakdown spectroscopy), not only may it serve to minimize the impact on the investigated sample, but also to optimize the laser and spectral parameters, or even to pave the way for real-time chemical analysis of the sample. To evaluate this impact and describe the plasma time behavior, electron temperature and density are calculated for plasma induced by double-pulse Nd:YAG laser with various (0–500 ns) inter-pulse delays. The parameters are calculated using various methods, such as Stark broadening, Boltzmann plot and Saha equation to provide complementary calculations for comparison. To ensure validity of the results, calibration of the measurement setup was performed. In the work, tungsten samples are investigated, because the W is chosen as the preferred material for plasma-facing components in future fusion devices such as ITER. Since LIBS method will be used to monitor tritium retention in ITER, the results may be utilized to improve the diagnostics.

Plasma defocusing in dual-pulse laser ignition

The paper presents simulation results of hydrogen-air mixture ignition by an ultraviolet followed by a near-infrared laser pulse. We used the three-temperature plasma model in a combination with the beam propagation method. Effect of plasma defocusing on the ignition kernel development is reported. It is shown that the plasma generated by the pre-ionizing pulse affects the position of the focal region of the second heating pulse with resulting changes in the distribution of the laser energy absorption, electron and radical production and ignition kernel dynamics. For the case with the defocusing effect we observed a shift of the peaks of translational and vibrational temperatures towards the direction of the laser pulse and two peaks on the axial profile of the electron temperature, reflecting local changes both in Joule heating and electron energy losses.

Displacement of energy deposition during formation of nanosecond laser plasmas by self-defocusing

The long-term hydrodynamics of laser generated plasma regions are dictated by the spatial distribution of the deposited laser energy. Using an integrated chemical-optical solver to track energy deposition from single and dual nanosecond laser pulses, we show that self-defocusing results in a biased growth of the plasma region towards the focusing lens. This displacement of energy deposition scales with the Rayleigh range and can be reduced by maximizing the beam divergence.

The characteristics of extreme ultraviolet emission from Gd plasma produced by dual pulse laser

The characteristics of extreme ultraviolet emission from Gd plasma produced by dual pulse laser

The plasma characteristics of femtosecond-nanosecond dual-pulse laser ablated soil

We report on the observation of dual-pulses laser-produced plasmas (DP-LPPs), following a femtosecond Ti: sapphire pulse laser ablate soil generated asubstantial numberof soil aerosol particle clusters of soil target and then a nanosecond Nd:YAG pulse laser re-ablated the soil aerosol particles clusters. The temporal evolution of the fs laser-produced plasmas (fs-LPPs) highlight a different in plasma plume expansion dynamics and particles clusters distributions where, the initial position and velocity of plasma plume expansion are 0.79 mm and 4.8 km/s, the terminal position is 2.2 mm and the velocity gradually become slower and slower, in the delay time range of 150 ns to 2.1 μs. There are three distribution states contains a columnar particle fluid flow region, “Mushroom cloud” fluid flow region, and arbitrary shape fluid flow region of the particles scattering images of different inter-pulse time at 1, 5, 9, 10, 30, 50, 200, 400 and 800 μs. Based on the Boltzmann plot method and Stark broadening, the plasma temperature and electron density is also investigated, the results shows that DP-LPPs optical emission spectrum (OES) has a narrow linear broadening and enhanced spectral intensity, associates with the higher plasma temperature and lower electron density compare with the single fs-LPPs.

Resonant dual-pulse laser ignition technique based on oxygen REMPI pre-ionization

This contribution investigates a novel laser ignition method based on a dual-pulse resonant pre-ionization scheme. The first laser pulse efficiently creates initial gas ionization (seed electrons) through a 2 + 1 resonantly-enhanced multiphoton ionization (REMPI) scheme targeting molecular oxygen (λ ~ 287.6 nm). This pulse is followed by a second non-resonant near-infrared pulse (λ = 1064 nm) for energy addition into the gas via inverse bremsstrahlung absorption. The sequence of two pulses creates a laser induced plasma that exhibits high peak electron number density and temperature (ne ~ 8 × 1017 cm-3 at t = 100 ns and T ~ 8000 K at t = 10 μs, respectively). These plasma parameters are similar to those attained for typical single-pulse near-infrared laser plasmas but with the advantage of substantially lower pulse energy (by factor of ~ 2.5) in the dual-pulse REMPI case. A combustion study focusing on ignition of propane/air mixtures shows that the dual-pulse REMPI method leads to an extension of the lean flammability limit, and an increase in combustion efficiency near the lean limit, as compared to laser ignition with a single NIR pulse. The measurement results and observed gas dynamics are discussed in the context of their impact on combustion applications.

Gas dynamic regimes observed in dual-pulse laser ignition

A numerical study of the gas dynamics induced by a dual-pulse laser pre-ionization plasma used in laser ignition applications is presented herein. Past experimental observations have revealed important differences in the gas dynamics of the dual-pulse plasma, generated by overlapping a pair of ultraviolet (UV) and near-infrared (NIR) pulses, as compared to those of single-pulse (typically near-infrared) laser breakdown that has been more commonly studied. The simulation results reported here show that the dual-pulse pre-ionization scheme can lead to various gas dynamic regimes depending on the axial offset of the focal points of the two beams along the optical axis. If the UV and NIR pulses are perfectly overlapped (no offset) the energy deposition is uniform along the optical axis, leading to the formation of a toroidal structure in the post-discharge cooling phase. Alternatively, if the NIR energy addition pulse is focused with a small axial offset, (i.e., upstream or downstream of the UV pre-ionization pulse by ~0.5 mm) then an asymmetric torus forms that exhibits a third lobe which propagates away from the main kernel (to the side where the NIR was focused). Finally, if the two beams are focused with a larger offset of ~2.5 mm (weaker coupling), then another regime with a fourth lobe can arise. The four main flow regimes revealed from the model are in agreement with OH* experimental chemiluminescence images. These flow regimes influence the development of the early flame kernels, therefore playing an important role in practical laser ignition applications.

Effect of dual-beam laser radiation for synthetic SnO2/Au nanoalloy for antibacterial activity

A facile synthetic method was reported to synthesis nanostructured alloy from SnO2/Au in just one step without further purification or washing by a dual ultra-fast pulsed laser ablation in liquid media technique. The dual ultra-fast technique was based on splitting the laser irradiation by beam splatter to produce two paths. Each path makes a laser ablation process on each target immersed in ultra-pure water. The physicochemical properties of the prepared sample were investigated by XRD, UV–visible spectrometer, TEM, and EDX. XRD technique showed the formation of crystalline structure from Au and SnO2, while UV-visible spectrometer showed the formation of the absorption peaks of SPR of Au and the metal oxide of SnO2, whereas TEM revealed the nanostructure formation of nanostructured alloy structure, but EDX confirmed that the formation alloy had the composition structure from Au and SnO2. Furthermore, its antibacterial activity showed the highly efficient against E. coli rather than Bacillus subtilis.

Fully Integrated Time-Gated 3D Fluorescence Imager for Deep Neural Imaging.

This paper presents a device for time-gated fluorescence imaging in the deep brain, consisting of two on-chip laser diodes and 512 single-photon avalanche diodes (SPADs). The edge-emitting laser diodes deliver fluorescence excitation above the SPAD array, parallel to the imager. In the time domain, laser diode illumination is pulsed and the SPAD is time-gated, allowing a fluorescence excitation rejection up to O.D. 3 at 1ns of time-gate delay. Each SPAD pixel is masked with Talbot gratings to enable the mapping of 2D array photon counts into a 3D image. The 3D image achieves a resolution of 40, 35, and 73μm in the x, y, and z directions, respectively, in a noiseless environment, with a maximum frame rate of 50 kilo-frames-per-second. We present measurement results of the spatial and temporal profiles of the dual-pulsed laser diode illumination and of the photon detection characteristics of the SPAD array. Finally, we show the imager's ability to resolve a glass micropipette filled with red fluorescent microspheres. The system's 420μm-wide cross section allows it to be inserted at arbitrary depths of the brain while achieving a field of view four times larger than fiber endoscopes of equal diameter.

Measurement of Simulated Debris Removal Rates in an Artificial Root Canal to Optimize Laser-Activated Irrigation Parameters.

Background and ObjectivesTo compare temporal rates of debris removal from an artificial root canal for three laser‐assisted irrigation modalities single‐pulse super short pulse (SSP), and two dual‐pulse X‐SWEEPS and AutoSWEEPS, and for two fiber‐tip (FT) geometries flat and radial, and to evaluate the dependence of the debris flushing rate on the delay between the SWEEPS laser pulse pair.Study Design/Materials and MethodsLaser‐assisted irrigation was performed with a pulsed Er:YAG laser operating in single‐pulse SSP and dual‐pulse SWEEPS laser modalities. The laser energy was delivered to the water‐filled model access cavity through a FT with either a flat or radial ending. The X‐SWEEPS modality delivered pairs of laser pulses separated by a fixed adjustable delay, while with the AutoSWEEPS modality the delay was automatically and repeatedly swept between 200 and 600 microseconds. The debris removal rate was determined with the use of a digital camera by measuring the rate at which a simulated debris was being flushed out of the artificial root canal.ResultsThe simulated debris removal rate of the AutoSWEEPS modality is almost three times higher compared with that of the SSP modality. Further, the flat FT outperforms the radial FT by a factor of more than five in the case of SSP, and by more than 10 with AutoSWEEPS. The X‐SWEEPS flushing rate exhibits strong dependence on the delay between the SWEEPS pulse pair, with the highest removal rate measured to be more than seven times higher in comparison with SSP.ConclusionDual‐pulse laser irrigation modalities (AutoSWEEPS and X‐SWEEPS) exhibit significantly higher simulated debris removal rates in comparison with the standard single‐pulse SSP laser‐assisted irrigation. As opposed to the previously reported dependence of pressure generation on FT geometry, the flat FT's simulated debris removal rate significantly outperforms the radial FT. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC

Laser Guiding of Three Phase Tesla Coil High Voltage Discharges

Guiding and triggering of discharges from a three phase Tesla coil type 280 kHz AC high voltage source using filaments created by a femtosecond Terawatt laser pulse. Without the laser the discharges were maximum 30 cm long. With the laser straight, guided discharges up to 110 cm length were detected. The discharge length was limited by the voltage amplitude of the Tesla coil. A significant reduction of the breakdown voltage threshold due to the pre-ionization of the air gap by laser pulse filamentation was observed. The lifetime of filaments is measured by using time-resolved fluorescence spectrum, and the lifetime of filaments generated by dual fs laser pulses was doubled due to the re-ionization by the succeeding pulse

Spectral Characterization of Collinear Double-Pulse Laser Induced Breakdown Spectroscopy (DP-LIBS) for the Analysis of the Chinese Traditional Medicine Artemisia annua

A collinear dual-pulse laser induced breakdown spectroscopy (DP-LIBS) method was employed to analyze Chinese traditional medicine Artemisia annua. The spectral intensities and signal-to-background ratios of magnesium (II) 279.54 nm, CN 388.29 nm, calcium (II) 393.37 nm, and iron (II) 404.27 nm were used to evaluate the optical emission characteristics of A. annua induced by DP-LIBS. The temporal evolution characteristics, inter-pulse time, and laser energy values were optimized. In particular, the electron density and the temperatures of the plasma were reported as functions of the delay time. The results showed that the DP-LIBS had stronger intensity and better accuracy compared to single-pulse (SP) LIBS. The enhancement factors obtained using DP-LIBS for Mg, CN, Ca, and Fe were 7.2, 8.9, 13.8, and 3.4, respectively. This study provides important information about A. annua.

Dynamics of dual-pulse laser energy deposition in a supersonic flow

Dynamics of plasma generated by the dual-pulse laser in a supersonic flow was studied numerically. The mathematical model includes species, momentum, electronic, vibrational and translational energy equations for the multicomponent ionized air. The model examines temporal dynamics of the formed air plasma and how it affects the drag, pressure signature and vorticity generation in a supersonic flow around a wedge. We observed that nonequilibrium plasmas is more effective in the drag reduction compared with the simultaneous thermal energy addition. The maximum drag reduction of around 50% and the maximum drag coefficient reduction of 30% was attained through the dual-pulse laser energy deposition. Variation of the plasma spot orientation did not significantly influence the drag reduction. We suggested that the surface pressure changes were not controlled by the vorticity generation but occurred due to the density changes and the formation of the low-density plasma spot.

Amelioration in the Detection of Chlorine Using Electric Field Assisted LIBS

The detection of chlorine and improvement in its detection has remained a challenge despite the use of a single pulse and a dual pulse laser induced breakdown spectroscopic technique (LIBS). In this article, we presented an alternate technique for improving the detection of chlorine (Cl) using LIBS in conjunction with an external electric filed. A comparison of the emission intensity enhancement and plasma parameters in the absence and presence of an external field has been also presented. The implication of the presented technique for the detection of Cl is much easier and inexpensive as compared with the dual pulse LIBS.

Collinear dual-pulse laser optical breakdown and energy deposition

A non-equilibrium model for laser-generated plasmas is used to represent collinear dual nano-second-pulse interactions. In the specific case considered, the breakdown is initiated with an ultraviolet (UV) laser pulse at 266 nm, which pre-ionizes the gas, and it is followed by a near-infrared (NIR) pulse at 1064 nm, which deposits significant energy into the ionized mixture. The model is validated against corresponding experiments, and simulation results are interrogated to understand key features of the plasma-kernel dynamics and the post-discharge hydrodynamics. The hydrodynamics of the non-equilibrium plasma is governed by the two-temperature Navier–Stokes equations accounting for both multiphoton ionization and inverse bremsstrahlung. The interaction between the laser beam and the plasma is modeled based on the radiative transfer equation. The temporal and spatial offsets of the two pulses can generate ionization kernels with different topology and dynamics. It is shown that the UV pre-ionization pulse can tailor the plasma region, leading to a larger ionized volume than would occur for a single-pulse breakdown, and it increases the efficiency of the energy deposition for the following NIR discharge. Vorticity in the early post-discharge phase is generated via baroclinic torque from the misalignment of the radial gradient of density (sudden gas expansion) and the strong pressure gradient (initiated by energy deposition from the laser beam). It is predicted that the collinear dual pulse can be designed to specify the plasma kernel size, shape, and maximum temperature in the breakdown phase, and the initial post-breakdown vorticity and plasma-core decay.

Study of nano particle stripping and composition inspection on wafer surface

Nano-scale particle stripping and inspection on silicon wafer are critical issues for Integrated Circuit(IC) manufacture industry. As more new materials are used in IC manufacture, not only particle itself but also its composition should be inspected. Particles are mainly adhered by the van der waals force. One of potential particle desorption method is laser cleaning which is environment friendly. However, the mechanism of laser cleaning is not clear and more studies should be done for laser ablation. In this paper, the kinetic process of nano particle on silicon wafer induced by nanosecond pulsed laser as well as the on-line detection method of particle composition were studied. A potential method of nano particle dynamic analysis and particle composition inspection were presented. A dual nanosecond pulse laser system both wavelengths at 532 nm is designed in which one laser pumps the particles away from wafer surface almost without damage, the other laser breakdowns the particles in air above the wafer surface to obtain the emission lines of the contaminated particles of 300 nm Cu by a spectroscopy with CCD. Particle motion trail in &lt;i&gt;z&lt;/i&gt; direction was observed after laser cleaning by analyzing particle spectral features. The particle dynamic model after stripping was established in which the resistance of air collision and gravity were included. And the model parameters were obtained by calculation using experimental results. The initial velocity of particle at the end of laser pulse and the average acceleration during laser interaction were calculated which were 7.6 m/s and 7.6 × 10&lt;sup&gt;8&lt;/sup&gt; m/s&lt;sup&gt;2&lt;/sup&gt; respectively. The sensitivity of the dual laser system was evaluated which was between 2.1 × 10&lt;sup&gt;13&lt;/sup&gt; to 5.1 × 10&lt;sup&gt;13&lt;/sup&gt; atoms/cm&lt;sup&gt;2&lt;/sup&gt;. As result, it is found that the gravity of the particle should not be ignored and the velocity divergence between different stripping particles is existed. The study not only provides a methodology for the study of laser-induced removal of nano particles on the wafer surface and laser induced nano particle dynamics, but also provides a potential method for the inspection of particle composition and pollution source monitoring on line in integrated circuit manufacture process. As the results were not the optimum one and further study should be done in which a better laser power density should be used.

Near-Surface Plasma Formed by Dual-Pulse Laser Action at Two Wavelengths on Titanium in Air

Spectra and structures of near-surface plasma torches were studied experimentally by measuring the specific mass loss and plume luminosity caused by dual-pulse laser radiation at wavelengths 1064 and 532 nm on titanium in air as functions of the time between laser pulses and their sequence. Dependences of the laser-plasma temperature and concentration of charged particles on the paired laser pulse parameters were established at laser radiation power densities q1064 ≤ 3.1·109 and q532 ≤ 2.7·109 W/cm2 for λ = 1064 and 532 nm. The optimal conditions for recording erosion plasma spectra had the initial effect from second-harmonic radiation with a time interval between pulses of 4–5 μs; for specific mass loss, 3–6 μs. The results were important for enhancing the efficiency of laser emission spectral analysis and laser-plasma processing of materials.

Potential use of laser-induced breakdown spectroscopy combined laser cleaning for inspection of particle defect components on silicon wafer

The contamination control of silicon wafer surface is more and more strict. Many investigations have been done to inspect defects on silicon wafer. However, rare studies have been reported on defect component inspection, which is also critical to trace the source of defects and monitor manufacturing processes in time. In order to inspect the components of contaminated particles on silicon wafer, especially with a high-speed, in-line mode and negligible damage, a dual nanosecond pulse laser system with both wavelengths at 532 nm is designed, in which one laser pumps the particles away from the wafer surface with negligible damage, the other laser breaks down the particles in the air above the wafer surface to obtain the emission lines of the contaminated particles by a spectroscopy with intensified charge coupled device. The sensitivity of the dual pulse laser system is evaluated. The particle dynamic process after pump is analyzed. The results in this work provide a potential on-line method for the semiconductor industry to trace the sources of defects during the manufacture process.