Increasing Laser Pulse Energy Research Articles

Piezoelectric Energy Harvester Based on LiNbO3 Thin Films.

This paper reports the results of the influence of the energy of laser pulses during laser ablation on the morphology and electro-physical properties of LiNbO3 nanocrystalline films. It is found that increasing laser pulse energy from 180 to 220 mJ results in the concentration of charge carriers in LiNbO3 films decreasing from 8.6 × 1015 to 1.0 × 1013 cm−3, with the mobility of charge carriers increasing from 0.43 to 17.4 cm2/(V·s). In addition, experimental studies of sublayer material effects on the geometric parameters of carbon nanotubes (CNTs) are performed. It is found that the material of the lower electrode has a significant effect on the formation of CNTs. CNTs obtained at the same growth time on a sample with a Cr sublayer have a smaller diameter and a longer length compared to samples with a V sublayer. Based on the obtained results, the architecture of the energy nanogenerator is proposed. The current generated by the nanogenerator is 18 nA under mechanical stress of 600 nN. The obtained piezoelectric nanogenerator parameters are used to estimate the parameters of the hybrid-carbon-nanostructures-based piezoelectric energy converter. Obtained results are promising for the development of efficient energy converters for alternative energy devices based on lead-free ferroelectric films.

Characterization of laser-induced vibration on concrete surface toward highly efficient laser remote sensing

Laser remote sensing (LRS) using irradiation of high-power laser pulses provides characteristic vibrations (CVs) which are accompanied by internal deterioration. While the principle of LRS is the same as that of the traditional hammering inspection, optimizing the irradiation parameters of laser pulses for vibrating samples is essential for effective LRS. In this study, the frequencies and magnitudes of CVs on a concrete specimen exhibiting a mock inside defect were evaluated by laser pulse irradiation and pendulum impact. When laser pulses were irradiated, the magnitude of CVs increased linearly with increasing laser pulse energy, and higher-order vibration was observed. On the other hand, an optimal spot size was indicated by the non-linear correlation between the fluence and the magnitude of CVs. To obtain an effective LRS, we propose that both high laser fluence and an optimized laser spot size are essential.

Synthesis of colloidal aluminum nanoparticles by nanosecond pulsed laser and the effect of external electric field and laser fluence on ablation rate

In this paper, the ablation of aluminum was induced by a Q-switched Nd:YAG laser (1064 nm, ~10 ns and 10 Hz) in ethanol at room temperature for producing colloidal nanoparticles. Two different experimental schemes (i.e. the electric field parallel, and perpendicular to the laser propagation path) were used to investigate the dependence of ablation rate on the external electric field characteristics and the laser fluence. The results show that at a constant laser fluence, regardless of the type of scheme, the ablation rate is increased in the presence of electric field. However, the characteristics of craters strongly depend on the direction of the electric field. The results also show that at both schemes with a constant electric field, the ablation rate rises when the laser fluence is increased. According to the results, it can be concluded that the ablation rate enhanced by applying electric field and increasing laser pulse energy.

Simulation Platform of Multi-Pulse Photoacoustic Microscopy Based on K-Space Pseudospectral Method

Photoacoustic imaging has emerged in the past decades. Compared with the traditional medical imaging mode, it has better imaging performance and has great development potential in the field of biological imaging. In traditional photoacoustic microscopy, a single laser pulse is generally used to irradiate the sample to produce photoacoustic signal. And sig-nal-to-noise ratio (SNR) is a very important indicator for photoacoustic im-aging. In order to obtain the image with high SNR, multiple acquisition or increasing laser pulse energy is usually adopted. The former will lead to slower imaging speed, and the latter will lead to photobleaching or pho-totoxicity. Here, we propose multi-pulse photoacoustic microscopy, the photoacoustic signals were stimulated sequentially using multiple laser pulses in each A line data acquisition. In order to verify the feasibility of this method, a multi-pulse photoacoustic imaging simulation platform is established using k-Wave toolbox. The performance of multi-pulse photo-acoustic imaging is verified through the three scanning modes of photoa-coustic microscopy A-scan, B-scan, and C-scan. The results indicate that the SNR is proportion to the number of laser pulses used, high SNR can be achieved by low-energy laser pulse. This work will help to expand the ap-plication of photoacoustic imaging.

Effect of lasing energy on the structure and optical and gas sensing properties of chromium oxide thin films

Chromium oxide (Cr2O3) thin films were prepared by the pulsed laser deposition (PLD) technique onto glass substrates using different laser pulse energies (500–900 mJ). The thickness of the prepared films ranged from 177.3 to 372.4 nm. The X-ray diffraction (XRD) study revealed that Cr2O3 thin films are amorphous, but they converted to the rhombohedral crystalline structure with space symmetry group after annealing at 300 °C for two hours. Furthermore, the atomic force microscopy (AFM) exhibited the formation of smooth and well-dispersed surfaces. The optical measurements in the wavelength range between 300 and 1100 nm confirmed that the optical energy gap of the prepared films decreased with increasing laser pulse energy, and a transition of the indirect type with a band gap of ≈ 3.90 eV was determined. The effect of the operation temperature on thin films’ sensitivity has been studied with the aim of optimizing the operation temperature as well as the response and recovery time for the prepared Cr2O3 thin films.

Investigation on Interface Morphology and Mechanical Properties of Three-Layer Laser Impact Welding of Cu/Al/Cu

In this study, laser impact welding technology was applied to fabricate a three-layer Cu/Al/Cu joint. A series of experiments were carried out to investigate the interface morphology and mechanical properties of the welding samples. Results revealed that different morphologies were generated at the upper and lower interfaces. The lower interface morphology transformed from straight to wavy as the collision point moved outward from the center along the radius. With the increase of laser pulse energy, the areas of upper and lower bonding regions expanded. When the laser energy was small, intermetallics and melting zones were absent and slight element diffusion occurred near the upper and lower interfaces. Melting zones occurred at the welding interface when the laser energy increased. Quantitative analysis by energy dispersive spectroscopy found that Al/Cu intermetallics may be produced in the melting region. Nanoindentation hardness test indicated that as the distance from the upper and lower interfaces decreased, the hardness of flyer plate and base plate increased. Two failure modes, that is, fracture failure at the upper and lower bonding interfaces, were observed under different laser energies.

Laser-structured high performance PVD coatings

Structured plastic components, which are used for flow-optimization, self-cleaning surfaces and optical applications, are usually produced by injection molding using structured tools. A suitable technique for structuring these tools on macro and nanometer scales is laser ablation, which offers a high level of accuracy and flexibility. The influence of laser treatments for the fabrication of nanostructures on the surface properties of steel has been extensively investigated. In contrast, there are only few studies dealing with the cause-effect mechanisms between a corresponding laser treatment and PVD (physical vapor deposition) hard coatings.This work deals with the influence of a laser nanostructuring on the properties of different CrAl-based PVD hard coatings. For this purpose, three coatings, one nitride (Cr,Al)N and one oxynitride (Cr,Al)ON, as well as one CrN/AlN nanolaminate were deposited on steel AISI 420 (X42Cr13, 1.2083) using a PVD process. The coatings were structured by means of an ultra-short pulsed (USP) laser with a varying laser pulse energy (Ep) ranging from Ep1=0.005mJ over Ep2=0.011mJ to Ep3=0.018mJ. On the one hand, an increasing laser pulse energy leads to significantly greater structural depths. This was quantified by confocal laser scanning microscopy (CLSM). On the other hand, it has been found that, in excess of a certain laser pulse energy, the universal hardness of the coatings decreases. By means of microstructural investigations, such as X-ray diffraction (XRD) and transmission electron microscopy (TEM), this effect was investigated and characterized. It was found that thermal effects induced during laser structuring lead to an increasing ratio of amorphous to crystalline domains of the PVD coating, causing the reduction in hardness. Finally, suitable combinations of PVD hard coatings and laser structuring parameters are recommended.

Measurement of the Hydrodynamic Efficiency of Laser Plasma at the “Kanal-2” Installation using Aluminum and Copper Targets

The results of experimental measurements of the hydrodynamic efficiency of laser plasma for aluminum and copper targets are presented. The studies were performed on the “Kanal-2” laser setup system using the ballistic pendulum method. The pressure in the interaction chamber was 10−4 Torr, the pendulum length was 145 mm, the mass of the pendulum with a target was 7.2 g. At the half-height pulse duration of 2.5 ns, the power density on the target surface was ∼1013 W/cm2. In the case of aluminum target, the hydrodynamic efficiency coefficient increased from 1.5% to 4.5% with increasing laser pulse energy from 5 J to 10 J, whereas it remained at the level of 5% for the copper target.

Laser-induced breakdown spectroscopic studies of calcite (CaCO3) marble using the fundamental (1064 nm) and second (532 nm) harmonic of a Nd:YAG laser

Calcium is the fifth most abundant element in the Earth’s crust and finds many applications in different fields of science and technology. Laser-induced breakdown spectroscopy (LIBS) was used for the analysis of naturally occurring calcite (CaCO3) marble at atmospheric pressure using the fundamental (1064 nm) and second (532 nm) harmonic of a Q-switched Nd:YAG laser. The emission spectra consist of neutral and singly ionized spectral lines of Ca and Mg, while traces of Al, Sr, and Na were also detected. The Ca lines were observed to dominate the shorter as well as longer wavelength regions and the 4s4d 3D2 → 4s4p 3P2 transition of Ca (I) at 445.74 nm possessed higher intensity than any other spectral line in the observed spectra. An increase in the signal intensity of the spectral lines was noted with the increase in laser pulse energy. The relative abundance of the pertinent elements was determined by integrated intensities of the strongest lines, and integrated intensities of all lines from each element and the result was 79.74% Ca and 15.49% Mg, revealing them as major constituting elements. The results of the LIBS technique agreed with the outcomes of the same sample studied for micro-chemical analysis using an electron probe micro analyzer coupled with energy dispersive x-ray spectroscopy. Self-absorption was noted for a doublet of singly ionized Ca (II) line at 397.1 nm. The experimentally observed integrated line intensities of six Ca (I) lines at 364.53, 443.80, 458.86, 526.18, 616.83, and 650.04 nm were used to extract the electron temperature (Te) using the Boltzmann plot method. The electron number density (Ne) was determined from the Stark broadening profile of a neutral Ca (I) line at 504.37 nm. The values of Te and Ne at a 0.05 mm distance from the target surface with a pulse energy of 40 mJ were found to be 8500 K and 3.53 × 1016 cm−3 for the 1064 nm laser. The same parameters were observed to be 6800 K and 3.87 × 1016 cm−3 for the 532 nm laser. The relationship between electron temperature and number density was found to be directly related to the laser irradiance, while inverse proportionality was observed for the distance (0.05–2.0 mm) from the target surface.

The Femtosecond Laser Ablation on Ultrafine-Grained Copper

To investigate the effects of femtosecond laser ablation on the surface morphology and microstructure of ultrafine-grained copper, point, single-line scanning, and area scanning ablation of ultrafine-grained and coarse-grained copper were performed at room temperature. The ablation threshold gradually increased and materials processing became more difficult with decreasing grain size. In addition, the ablation depth and width of the channels formed by single-line scanning ablation gradually increased with increasing grain size for the same laser pulse energy. The microhardness of the ablated specimens was also evaluated as a function of laser pulse energy using area scanning ablation. The microhardness difference before and after ablation increased with decreasing grain size for the same laser pulse energy. In addition, the microhardness after ablation gradually decreased with increasing laser pulse energy for the ultrafine-grained specimens. However, for the coarse-grained copper specimens, no clear changes of the microhardness were observed after ablation with varying laser pulse energies. The grain sizes of the ultrafine-grained specimens were also surveyed as a function of laser pulse energy using electron backscattered diffraction (EBSD). The heat generated by laser ablation caused recrystallization and grain growth of the ultrafine-grained copper; moreover, the grain size gradually increased with increasing pulse energy. In contrast, no obvious changes in grain size were observed for the coarse-grained copper specimens with increasing pulse energy.

Spatiotemporal evolution of the plasma from dual-pulsed laser-induced breakdown in an atmospheric air

The spatiotemporal evolution of dual-pulsed laser-induced breakdown (DPLIB) was experimentally investigated in a quiescent atmospheric air. DPLIB with time intervals between pulses of 30–100 ns and pulse energies of 10–30 mJ were compared to a single laser-induced breakdown of the same total energy. An intensified CCD camera was used to capture direct images from the onset of the breakdown until 300 ns after the breakdown. The spatial and temporal temperature and electron number density were obtained from the N II spectrum at 500 nm. With increasing laser pulse energy, the breakdown perimeter, temperature and electron number density all increase. For DPLIB, the second breakdown occurs on the outside axial edges of the first breakdown increasing the breakdown perimeter. The uneven distribution of energy to the plasma creates an uneven temperature distribution. The electron number density is increased at the edges of the DPLIB for times less than 150 ns after the first breakdown. Depending on the electron number density of the first breakdown and the focal point location of the second breakdown, the second breakdown could occur on either the near side (closest to the focusing lens) or the far side (furthest from the focusing lens) of the focal point in the axial direction of the laser beam.

Laser Indirect Shock Welding of Fine Wire to Metal Sheet.

The purpose of this paper is to present an advanced method for welding fine wire to metal sheet, namely laser indirect shock welding (LISW). This process uses silica gel as driver sheet to accelerate the metal sheet toward the wire to obtain metallurgical bonding. A series of experiments were implemented to validate the welding ability of Al sheet/Cu wire and Al sheet/Ag wire. It was found that the use of a driver sheet can maintain high surface quality of the metal sheet. With the increase of laser pulse energy, the bonding area of the sheet/wire increased and the welding interfaces were nearly flat. Energy dispersive spectroscopy (EDS) results show that the intermetallic phases were absent and a short element diffusion layer which would limit the formation of the intermetallic phases emerging at the welding interface. A tensile shear test was used to measure the mechanical strength of the welding joints. The influence of laser pulse energy on the tensile failure modes was investigated, and two failure modes, including interfacial failure and failure through the wire, were observed. The nanoindentation test results indicate that as the distance to the welding interface decreased, the microhardness increased due to the plastic deformation becoming more violent.

Controlling residual hydrogen gas in mass spectra during pulsed laser atom probe tomography

Residual hydrogen (H2) gas in the analysis chamber of an atom probe instrument limits the ability to measure H concentration in metals and alloys. Measuring H concentration would permit quantification of important physical phenomena, such as hydrogen embrittlement, corrosion, hydrogen trapping, and grain boundary segregation. Increased insight into the behavior of residual H2 gas on the specimen tip surface in atom probe instruments could help reduce these limitations. The influence of user-selected experimental parameters on the field adsorption and desorption of residual H2 gas on nominally pure copper (Cu) was studied during ultraviolet pulsed laser atom probe tomography. The results indicate that the total residual hydrogen concentration, HTOT, in the mass spectra exhibits a generally decreasing trend with increasing laser pulse energy and increasing laser pulse frequency. Second-order interaction effects are also important. The pulse energy has the greatest influence on the quantity HTOT, which is consistently less than 0.1 at.% at a value of 80 pJ.

Heat transfer and material ablation in hybrid laser-waterjet microgrooving of single crystalline germanium

A numerical model describing the heat transfer and material ablation in a hybrid laser-waterjet microgrooving process for a single crystalline germanium (Ge) is developed, considering the relevant physical phenomena involved, such as laser-induced plasma (or optical breakdown) in water, laser beam attenuation in the plasma zone, heat transfer in Ge substrates, and waterjet cooling and impinging effects. The model is then verified, which shows that the respective calculated and measured quantities are in reasonably good agreement. A numerical simulation study is then carried out using the developed model and demonstrates that the shielding effect of the laser-induced plasma increases with the laser pulse energy. In addition, the irradiated material can be expelled by a waterjet at its soft-solid status, and heat accumulation in the workpiece is effectively removed by the waterjet cooling effect during the off-pulse period, so that laser heating induced thermal damage is minimized. The effect of processing parameters on the ablation process is also analysed. It has been noticed that an increase in laser pulse energy leads to a deeper groove, and an increase in the applied water pressure decreases the threshold workpiece temperature for material removal.

Micro Surface Texturing of Alumina Ceramic with Nanosecond Laser

In order to fabricate micro surface textures on alumina ceramic, the effects of single pulse intervals processing and ring cutting processing on the laser surface textures were discussed. The advantages and disadvantages between the two kinds of processing method were compared. The crater diameter and depth increase with the increase of laser pulse energy, and the increasing number of pulses significantly affects the crater depth for the single pulse intervals processing. As for the ring cutting processing method, micro-pit depth changes with the average power, whereas the micro-pit diameter mainly changes with scan radium. By optimizing laser processing parameters the micro-pit dimensions could be independently controlled. These two methods could process micro-pits with different diameters and depth on alumina ceramic.

Determination of plasma temperature and electron density of iron in iron slag samples using laser induced breakdown spectroscopy

Plasma temperature and electron density of iron in iron slag samples taken from a local plant is studied. Optimal experimental conditions were evaluated using Nd: YAG laser at 1064 nm. Some toxic elements were identified and quantitative measurements were also made. Plasma temperature and electron density were estimated using standard equations and well resolved iron spectral lines in the 229.06-358.11 nm region at 10, 20, 30 and 40 mJ laser pulse energy with 4.5 μs delay time. These parameters were found to increase with increase in laser pulse energy. The Boltzmann distribution and experimentally measured line intensities support the assumption that the laser-induced plasma was in local thermal equilibrium. It is worth mentioning that iron and steel sector generates tons of solid waste and residues annually containing variety of contaminants which can be harmful to the environment and therefore knowledge, proper analysis and investigation of such iron slag is important.

Experimental investigation of underwater laser beam micromachining (UW-LBμM) on 304 stainless steel

Fabrication of miniaturized components provides a challenge to the manufacturing industries and to meet the challenges many unconventional machining methods are developed, among which laser beam micromachining (LBμM) is one. But, thermal effects such as recast layer, heat-affected zone (HAZ), debris, and thermal cracks are commonly observed in LBμM. So, in order to minimize the thermal effects, underwater laser beam micromachining (UW-LBμM) came into existence. In this paper, experiment on UW-LBμM is reported using a Q-switched Nd:YAG laser for fabricating microchannels on 304 stainless steel. The effect of input process parameters (scanning speed, number of scan, laser pulse energy) on output responses (kerf width, kerf depth, surface roughness) of microchannel is studied. Laser micromachined channels are characterized by using optical microscopy, surface profilometer, scanning electron microscopy, and energy dispersive X-ray spectroscopy. It is observed that the dimensions of kerf width and kerf depth are low at lower number of scan, laser pulse energy, and higher scanning speed. The surface roughness decreases with decrease in number of scan and increase in laser pulse energy. Minimum surface roughness is achieved at scanning speed of 300 μm/s. The recast layer and debris are minimum during UW-LBμM compared to LBμM. Elemental comparison is carried out inside and in the surroundings of microchannel.

Formation of a cathode plasma jet in a laser-induced vacuum discharge

The process of formation of micropinch structures in the plasma of a vacuum discharge initiated by a laser pulse on the cathode is studied. It is demonstrated that the micropinch formation takes place mainly in the substance evaporated by the laser pulse upon the discharge initiation. The size of the hot region of the plasma jet and the distance from the cathode to the micropinch increase with increasing laser pulse energy.

Study of Composition and Morphology of Cadmium Oxide (CdO) Nanoparticles for Eliminating Cancer Cells

The effects of substrate temperature on the structural, optical, medical and electrical characteristics of Cadmium Oxide (CdO) films are investigated in the current study. Films are deposited on glass substrate at different temperatures, ranged between 450–600 oC, using Spray Pyrolysis Technique. According to X–Ray Diffraction (XRD), it is found that the films are polycrystalline and Cadmium Oxide (CdO) is of a hexagonal wurtzite structure which the preferred direction of its crystal plane is (002). The maximum optical transmittance of films is more than 85%. The size of crystallites is calculated with the maximum value in 500o C. Furthermore, Cadmium Oxide (CdO) nanoparticles were synthesized in deionized water by laser ablation of Cadmium plate. In the current paper, the effects of laser pulse energy and wavelength on the characteristics of Cadmium Oxide (CdO) nanoparticles were studied. Analyses of Transmission Electron Microscope (TEM) were confirmed that size distribution of Cadmium Oxide (CdO) nanoparticles is reduced by increase in laser pulse energy. Fluorescence spectrum of Cadmium Oxide (CdO) nanoparticles shows violet emission accompanied by blue and green band. UV emission with high intensity shows that nanostructure of Cadmium Oxide (CdO) is of a little deficiency. Also, the current study aims to study the linear and non–linear optical characteristics of Cadmium Oxide (CdO) nanoparticles and their applications. Firstly, fluorescence spectrum, as a linear characteristics of Cadmium Oxide (CdO), as well as second harmonic generation and two photons absorption, as non–linear characteristics of Cadmium Oxide (CdO), are studied. Then, some aspects of medicinal and pharmaceutical applications of Cadmium Oxide (CdO) nanoparticles for eliminating cancer cells such as the effect of Cadmium Oxide (CdO) nanoparticles on DNA of human cancer cells and the interaction of Cadmium Oxide (CdO) nanoparticles with DNA of cancer cells are originally investigated. It should be noted that the range of considered parameters are separately clarified and explained in each of related sections (Figure 1).

Determination of Iron in Water Solution by Time-Resolved Femtosecond Laser-Induced Breakdown Spectroscopy**supported by the Russian Science Foundation (agreement #14-50-00034) (measurements of limit of detection), Russian Foundation for Basic Research (NK 15-32-20878/15) obtained in the frame of “Organization of Scientific Research” in the Far Eastern Federal University supported by Ministry of Education and Science of Russian Federation

The influence of the energy of femtosecond laser pulses on the intensity of Fe I (371.99 nm) emission line and the continuous spectrum of the plasma generated on the surface of Fe3+ water solution by a Ti: sapphire laser radiation with pulse duration < 45 fs and energies up to 7 mJ is determined. A calibration curve was obtained for Fe3+ concentration range from 0.5 g/L to the limit of detection in water solution, and its saturation was detected for concentrations above 0.25 g/L, which is ascribed to self-absorption. The 3σ- limit of detection obtained for Fe in water solution is 2.6 mg/L in the case of 7 mJ laser pulse energy. It is found that an increase of laser pulse energy insignificantly affects on LOD in the time-resolved LIBS and leads to a slight improvement of the limit of detection.