Influence Of Laser Intensity Research Articles

Influence of Laser Intensity and Location of the Fermi Level on Tunneling Processes for High-Harmonic Generation in Arrayed Semiconducting Carbon Nanotubes

Influence of Laser Intensity and Location of the Fermi Level on Tunneling Processes for High-Harmonic Generation in Arrayed Semiconducting Carbon Nanotubes

Influence of laser intensity and BaTiO3 content on the surface properties of 3YSZ.

Zirconia-based dental implants are in direct contact with living tissues and any improvements in their bioactivity and adhesion to the tissues are highly welcome. In this study, different ratios of barium titanate (BT) were added to 3mol% yttria-stabilized zirconia (3YSZ) through conventional sintering. The laser-texturing technique was also conducted to improve the biological performance of 3YSZ ceramics. The composition and the surface of the prepared composites were characterized by X-ray diffraction and scanning electron microscopy (SEM), respectively. The roughness and surface wettability of the composites were also measured. Furthermore, MC3T3-E1 pre-osteoblast cells were used for the in vitro experiments. Cell viability was evaluated using a commercial resazurin-based method. Morphology and cellular adhesion were observed using SEM. Based on the results, the laser texturing and the barium titanate content influenced the surface characteristics of the prepared composites. The laser-textured 3YSZ/7mol% BT composites showed a lower water contact angle compared to the other samples, which indicated superior surface hydrophilicity. The cell viability and cell adhesion of 3YSZ/BT composites increased with the rise in the barium titanate content and laser power. An elongated cell morphology and apatite nucleation were also observed by the BT content. Overall, the laser-treated 3YSZ/5 and 7mol% BT composites may be promising candidates in hard tissue repair due to their good cell response.

Ellipticity properties of symmetric molecules <inline-formula><tex-math id="M2">\begin{document}$ {\text{H}}_{\text{2}}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221946_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221946_M2.png"/></alternatives></inline-formula> in strong and short-wavelength laser fields

Ellipticity properties of high-order harmonic generation (HHG) from symmetric molecules <inline-formula><tex-math id="M6">\begin{document}$ {\text{H}}_{\text{2}}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221946_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221946_M6.png"/></alternatives></inline-formula> in strong and short wavelength (less than 800nm) laser fields are numerically investigated. In this study, the ellipticity of harmonic is compared with the corresponding harmonic spectrum and dipole, and the calculation results are analyzed and the results obtained at different laser intensities, different laser wavelengths, different internuclear distances and different orientation angles are compared with each other. Our numerical simulations show that the influences of laser intensity, laser wavelength, internuclear distance and orientation angle on the ellipticity of harmonic are different. Especially in a two-center interference region, the excited state plays an important role in the HHG, but the effects of the excited state on the ellipticity of harmonic are different at different orientation angles. Further analysis shows that these different effects are due to the influence of the excited state on the harmonic yield. Using the numerical scheme, it is determined that in the two-center interference region, the excited state plays an important role in the parallel harmonic spectrum, while the effects of the excited state on the perpendicular harmonics at different angles are all very small, which results in different phase differences between the accurate harmonic spectrum and the harmonic spectrum only returning to the ground state. Overall, the relative yields of the accurate perpendicular harmonics are lower (higher) than those of the accurate parallel harmonics, but the intensities of the perpendicular harmonics, which only return to the ground state, are comparable to (or farther away from) those of the parallel harmonics which are only to return to ground state in the two-center interference regions. Therefore, the small (large) intensity ratio between the accurate perpendicular harmonic and accurate parallel harmonic can be attributed to the contributions of the excited state to harmonics. Then we can conclude that the harmonic spectra that only go back to the ground state show high (small) ellipticity, whereas the accurate harmonic spectra show small (high) ellipticity, resulting in a strong angle dependence of the influence of the excited state on the ellipticity of harmonic. In addition, in the high-order harmonic plateau region, the relative yields of harmonics can be well predicted by the corresponding dipoles, indicating the applicability of tunneling pictures and plane wave approximation in the strong and short-wave laser fields. When the ellipticity of harmonic occurs in the interference region due to the two-center characteristics of the symmetric potential, the results show that the polarization measurement can also be used to detect the structures of symmetric molecules and track the dynamic behaviors of excited states.

Laser‐induced phonon and magnon properties of NiO nanoparticles: A Raman study

AbstractIn the present study, the influence of laser intensity on phonon and magnon properties of nickel oxide (NiO) nanoparticles were extensively studied using room temperature Raman spectroscopy. The required NiO nanoparticles were synthesized using a simple sol–gel method. The structural and morphological properties were characterized using powder X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), and transmission electron microscopy (TEM) techniques. The rarely reported surface optical (SO) phonon modes of NiO nanoparticles were observed and well‐studied using the dielectric continuum (DC) model. A mismatch between the experimental and DC model SO phonon wavenumbers were observed and is attributed to one magnon‐induced first order phonon shift. The difference between the experimental and DC model SO phonon wavenumbers were reduced with increase in laser power, which indicates the diminishing behavior of magnon excitations. The laser power dependency of highly distinguishable two magnon (2 M) excitation of NiO nanoparticles were well studied. The 2 M modes were experienced a red shift and decrease in intensity with increase in laser power.

A Parametric Investigation of Corneal Laser Surgery Based on the Multilayer Dynamic Photothermal Model.

Corneal laser surgery is a widely used method for the treatment of ocular myopia, hyperopia, and astigmatism. Although it is a well-established technique, the photothermal properties of the cornea are often overlooked, causing unexpected changes in temperature during laser irradiation. Therefore, there is a need for further investigation of the temperature response of the cornea under laser irradiation. In the present work, a photothermal corneal numerical model is presented, assuming the stratification of the cornea with laser ablation in an uncoagulated layer, a coagulated layer, a dehydrating layer, a dried layer, and a carbonized layer. The modified Pennes' bioheat transfer equation and Lambert-Beer's law are applied to simulate heat transfer in the corneal tissue during laser irradiation. And the corneal dynamic photothermal parameters are considered in the proposed model. The central surface temperature, the boundary and thickness of each layer, and the thermal damage during laser irradiation are investigated. From the model, it was found that in the steady-state process, the thickness of the coagulated layer was 2.6, 14.4, and 52.4 times larger than that of the dehydrating layer, the dried layer, and the carbonized layer, respectively. The thickness of the corneal thermal damage gradually increased, and reached a peak of 0.196 mm at about 18.2 ms. Subsequently, it sharply decreased by 0.01 mm before stabilizing. On this basis, the influence of laser intensity is investigated. The parametric investigation and analysis presented provide a theoretical basis for corneal laser surgery, which can be used to improve our understanding of laser-tissue surgery.

Characterization of microcraters fabricated on the silicon surface by single and multi-pulse laser ablation at various laser intensities

Microcraters on the silicon surface were fabricated with the help of a nanosecond pulsed laser. The features of microcraters fabricated with single laser pulse and pulse trains of various laser intensities were analyzed. In case of single pulse, the diameter and depth of micro-crater rise with the laser fluence and achieve saturation at higher laser intensities. For the range of fluence 62–122 J/cm2, the mass of ablated material was in the range of 0.27 × 10−9–2.69 × 10−9 g/pulse. Numerically simulated temperature trends were compared with the measured crater depths. The influence of laser intensity on the target temperature and onset time to melt/boil were also investigated. In case of pulse trains, the reduction in material removal efficiency is attributed to the plume shielding and accumulation of ablated material on the crater walls. We demonstrated that the laser intensity and number of laser pulses can be used to control the morphology of a microcrater.

Characteristic analysis of light and heat transfer in photothermal therapy using multiple-light-source heating strategy

Nanoparticles enhanced laser-induced thermal therapy (LITT) is an emerging method for early stage tumor treatment. One of the major issues challenging this technique is the accurate heating of the cancerous tissue without influencing the nearby healthy tissue. Owning to its outstanding optical, chemical, and biological properties, gold nanoparticles (GNPs) have been frequently applied to act as nanosource of heat for selective heating of tumor. In the present work, we studied the GNPs enhanced LITT theoretically. The bioheat transfer model under laser irradiation was established by the finite element method. The influences of laser intensity, GNPs volume fraction, anisotropic scattering characteristics of nanoparticles, convective heat transfer coefficient, and laser incident angle were investigated, respectively. On this basis, different treatment strategies, i.e. single heat source and multiple heat sources, were also explored. It is found that for single dose therapy, i.e. the whole tumor was damaged in one-time treatment, the efficacy is almost the same for oblique and vertical laser incident. However, for fractionated therapy, i.e. the tumor was totally damage after a series of treatments, the efficacy of oblique laser irradiation is better than that of vertical laser irradiation. Furthermore, the hyperthermia efficacy of multiple heat sources is much better than that of single heat source, which means that it can be applied in GNPs enhanced LITT to improve the photothermal therapy efficacy.

Experimental investigation of laser engraving quality on paper.

Laser engraving technology is a type of laser processing technology, widely used for product coding, marking, and so on. A large amount of research has reported the results of metal surface engraving; however, few research results, to the best of our knowledge, have provided theoretical support for the application of paper packaging laser engraving. In this paper, the quality of paper laser engraving is investigated by experimental methods. First, various phenomena appearing in paper carving were studied, including plant fiber burning, charcoal, and edge marks; second, the main factors affecting the quality of laser engraving are researched, and the influence of laser intensity and the preset width of carving marks on the engraving quality are discussed. The results show that the engraving precision is the best when the laser power is 11 W and the preset width is small (0.26 mm). Finally, the laser engraving precision of UV coated paper is studied, and the effect of UV material melting and secondary crystallization on engraving the quality of paper laser engraving quality is discussed. When the laser power is small, the maximum and minimum values of UV film melting and secondary crystallization engraving trace are relatively small as well; further, when the laser power increases, the maximum width of engraving is basically consistent with the preset width, and the precision of laser engraving is optimal.

Effect of 1070 nm laser intensity on parameters of In0.3Ga0.7As solar cell

The photoelectric properties of In0.3Ga0.7As solar cells applied in laser wireless power transmission (LWPT) were studied when they were irradiated by 1070 nm continuous wave (CW) laser of various intensities. The influences of laser intensity on solar cell parameters extracted by the pollination algorithm were analyzed quantitatively. Results show that the conversion efficiency of the cell rose to the maximum and then decreased rapidly in the laser intensity range of 50–900 mW/cm2. With higher energy laser irradiation, the rise of ideality factor and reverse saturation current would lead to the degradation of voltage at the maximum power point, which was the main reason for the decrease of conversion efficiency. The results provide the basis for choosing the appropriate input energy in the case of different transmission systems.

Surface characterization and tribological performance of laser shock peened steel surfaces

Laser shock peening (LSP) is a preeminent surface treatment technique that can surpass many of the modern surface modification processes. Though the wear and surface hardening behavior of the LSP treated surfaces has been extensively investigated, the friction behavior and surface morphological changes due to LSP are not well explored. Hence, the present study focuses on the effect of LSP process parameters on surface morphology and tribological behavior of 1045 steel surfaces. More specifically, the influence of laser intensity on surface roughness and its effect on the coefficient of friction (COF) and transfer layer formation were investigated. The results show that the COF decreased with increasing laser intensity up to a threshold intensity, thereafter, the COF increased with increasing laser intensity. These variation in COF was attributed to the change in surface morphology as a result of applied laser intensity. As the laser intensity increased to a threshold value, the COF decreased as a result of surface strengthening and roughening effects. Beyond the threshold laser intensity, the COF increased as a result of the dominant surface roughening effect.

Periodic spectral modulations of low-energy, low-charge-state carbon ions accelerated in an intense laser–solid interaction

We report experimental observation of periodic modulations in the energy distribution of C1+ ions dominantly accelerated in the interaction of a 15 μm thick tape target with intense laser pulses of intensities ∼1018 W/cm2 in a defocused configuration. Moreover, the influence of laser intensity on the acceleration of low- and high-charge-state species of carbon ions is observed. Two-dimensional (2D) particle-in-cell simulations elucidate the dynamics of ionization-dependent acceleration of different species in different laser focusing conditions. By comparison, 1D simulations suggest that the modulations of C1+ ions are due to the longitudinal recirculation dynamics of hot electrons in the target, which modulates the sheath field for acceleration of C1+ ions.

Formability of micro-gears fabrication in laser dynamic flexible punching

A novel laser dynamic flexible punching process is employed to fabricate micro-gears to address the difficulties in punch-to-die alignment in the conventional micro-punching process. In this process, induced shockwaves act as micro-punches and soft punch acts as the media to transmit pressure. The influences of laser intensity, foil thickness and grain size on dimensional accuracy and rollover diameter have been investigated experimentally. In addition, the changes in the hardness and elastic modulus of the workpiece after the laser shock effect are characterized by nano-indentation experiments. It is revealed that the dimensional accuracy is optimal when the laser intensity is 5.6GW/cm2, but the laser intensity has little effect on the rollover diameter. Punched gears of thicker foils result in worse dimensional accuracy and larger rollover diameter. Foils annealed at 350°C achieve the best punching accuracy but compromise with regard to the maximum rollover diameter. Furthermore, both the nano-hardness (9.92%) and elastic modulus (14.37%) are improved after the laser shock effect, as the evidence of an increase of surface strength and material stiffness. The proposed method, laser dynamic flexible punching, will potentially lead to new methods for micro-gears fabrication in the future.

Experimental investigation of the influence of laser intensity on the quality of Einstein-Podolsky-Rosen entangled photons

Using spontaneous parametric down conversion, polarization post selection and coincidence counting technique, the polarization Einstein-Podolsky-Rosen (EPR) entangled states are prepared. Experimental studies on the efficiency, contrast and fidelity with different pump laser intensities are performed systematically. The results show that the pump laser intensity distinctly influences the quality of entangled photons, especially the contrast and the fidelity. On the other hand, the pump efficiency of entangled photons is almost invariable, namely the entangled source brightness increases linearly with the increase of pump laser power.

Photothermal response of hollow gold nanoshell to laser irradiation: Continuous wave, short and ultrashort pulse

This paper is to investigate numerically the photothermal response of the most common size of gold nanoshell (AuNS) in an aqueous medium for biomedical applications. Three types of laser light irradiate the particle; a continuous-wave (CW), short (nanosecond) and ultrashort (femtosecond) pulse laser. The spatiotemporal evolution of the temperature profile inside and around the AuNS is computed using a numerical framework based on the finite element method (FEM). For CW and nanosecond (ns) pulse laser where the AuNS’s electrons and lattice are at thermal equilibrium, the ordinary heat diffusion equation is used to describe the heat transfer to the surrounding water. For femtosecond (fs) pulse laser, due to the inexistence of the thermal equilibrium, a two-temperature model (TTM) is used to describe the heat transfer processes occurring in the AuNS and the normal heat diffusion equation is used for the heat flux calculation at the particle/water interface. For each case, the influence of laser intensity on the maximum temperature reached at the particle/water interface is studied. The aim of this study is to provide a description for the fundamentals of heat release of AuNSs and useful insights for the development of these particles for biomedical applications such as drug delivery, photothermal cancer therapy and optoporation of cells.

Theoretical investigation of 2+2 resonance enhanced multi-photon ionization probability

The analytic formula of the ionization probability in the process of 2+2 resonance enhanced multi-photon ionization (REMPI) is derived from the dynamic rate equation about the interaction of photon and material. Based on the formula, the influence of laser intensity, laser pulse duration and collision relaxation rate on the ionization probability is investigated theoretically. It is shown that the ionization probability increases with the laser intensity and laser pulse duration. The ionization probability will get to one until two steps saturation with the increase of laser intensity. After that, the ionization probability will oscillates narrowly around the saturation value if the laser intensity increases further. The results also show that the ionization probability will decrease in linear manner nearly with the increase of collision relaxation rate. But the variation is small. So the influence of the collision relaxation rate (or even sample pressure) on the ionization probability can be ignored. In the practical use of REMPI, higher sample pressure will reduce the intensity of the detection signal is due to the collision complex of the positive and negative ions. This will reduce the collection efficiency of the ions, and influence the magnitude of the ion signal further.

Synthesis and characterization of potential iron–platinum drugs and supplements by laser liquid photolysis

Highly crystalline nanospherical iron-platinum systems were produced by 248 nm laser irradiation of a liquid precursor at different laser fluences, ranging from 100-375 mJ/cm(2). The influence of laser intensity on particle size, iron composition, and structure was systematically investigated. Different nanostructures of iron-platinum alloy and chemically disordered iron-platinum L10 phase were obtained without annealing. The prepared precursor solution underwent deep photolysis to polycrystalline iron-platinum nanoalloys through Fe(III) acetylacetonate and Pt(II) acetylacetonate. Fe(II) and Pt(I) acetylacetone decomposed into Fe(0) and Pt(0) nanoparticles. We found that the (001) diffraction peak shifted linearly to a lower angle, with the last peak shifting in opposition to the others. This caused the face-centered cubic L10 structure to change its composition according to laser fluence. The nanostructures were shown to contain iron and platinum only by energy-dispersive spectroscopy at several spots. The response of these iron-platinum nanoparticles to infrared depends on their stoichiometric composition, which is controlled by laser fluence.

Tensile strength of fine pitch QFP lead‐free soldered joints with diode laser soldering

PurposeThe purpose of this paper is to investigate the laser soldering of fine pitch quad flat package (QFP) devices using lead‐free solders and solder joint reliability during thermal cycling.Design/methodology/approachQFP devices were selected as the test vehicles and were soldered with four alloy types, Sn37Pb, Sn3.5Ag, Sn3.8Ag0.7Cu and Sn3.8Ag0.7Cu0.03Ce. The experimental samples were QFP‐256 devices with lead‐free solder paste on the printed circuit boards. The packages were dried for 24 h at 125°C prior to reflow soldering. Soldering experiments on the QFP devices were carried out with an infrared (IR) reflow soldering oven and a diode laser (DL) soldering system. Reflow soldering was performed at peak temperatures of 210°C (SnPb), 240°C (SnAgCu and SnAgCuCe) and 250°C (SnAg), as determined on the boards. Pull testing was adopted to evaluate the tensile strength of the four solders using an STR–1000 micro‐joint strength tester.FindingsThe tensile force of the QFP micro‐joints increased as laser intensity increased when it was less than an “optimal” value. The maximum tensile force of the QFP micro‐joints was gained when the laser intensity had increased to 2,165, 2,127, 2,165 and 2,064 W/cm2, depending on the alloy used. The thermal fatigue performance of three lead‐free solder joints, SnAgCuCe, SnAgCu and SnAg, was determined to be superior to that of the eutectic SnPb alloy. After soldering without thermal cycling tests, the fracture morphology of soldered joints exhibited characteristic toughness fracture with both of the soldering methods. After 700 thermal cycles, the fracture mechanism was also toughness fracture, nevertheless, the dimples became large. The fracture morphology of the soldered joints subjected to 1,500 thermal cycles indicated brittle intergranular fracture on the fracture surface and no intense plastic deformation appeared before fracture with IR soldering. For DL soldering, the pull fracture model of the SnAgCuCe was completely ductile in the soldered joint with 1,500 thermal cycles.Originality/valueThe paper usefully investigates the influence of laser intensity on the tensile strength of different soldered joints and the solder joint reliability during thermal cycling.

Subwavelength Direct Laser Patterning of Conductive Gold Nanostructures by Simultaneous Photopolymerization and Photoreduction

This article presents a new method for fabricating highly conductive gold nanostructures within a polymeric matrix with subwavelength resolution. The nanostructures are directly written in a gold precursor-doped photoresist using a femtosecond pulsed laser. The laser energy is absorbed by a two-photon dye, which induces simultaneous reduction of gold in the precursor and polymerization of the negative photoresist. This results in gold nanoparticle-doped polymeric lines that exhibit both plasmonic effects, due to the constituent gold nanoparticles, and relatively high conductivity (within an order of magnitude of the bulk metal), due to the high density of particles within these lines. Line widths from 150 to 1000 nm have been achieved with this method. Various optically functional structures have been prepared, and their structural and optical properties have been characterized. The influence of laser intensity and scan speed on feature size have been studied and found to be in agreement with predictions of a mathematical model of the process.

Simulation study of Hohlraum experiments on SGIII-prototype laser facility

The Hohlraum physics experiments performed on the SGIII-prototype laser facility are simulated by using our two-dimensional radiation hydrodynamic code LARED-H, and the influence of laser intensity on the two-dimensional Hohlraum simulations is studied. Both the temporal radiation temperature and the x-ray spectrum from the simulations agree well with the observations, except that the simulated M-band fraction (greater than 2 keV) is obviously smaller than the observation. According to our study, the coupling efficiency from laser to x-ray is around 70% for SGIII-prototype laser facility Hohlraums.

Mass transport in laser surface nitriding involving the effect of high temperature gradient: Simulation and experiment

A self-consistent diffusion model has been employed to simulate the atomic nitrogen transport in titanium alloy with the coupling effect of both initial activated nitrogen concentration and high temperature gradient. Transport equations are solved through coupling the transient heat transfer equation and incorporating the surface physical phenomena in the governing equations as boundary conditions. For comparisons, laser gas nitriding of Ti6Al4V alloy has been performed by means of a pulsed Nd:YAG laser irradiation in a controlled nitrogen chamber. Results indicate that the simulated nitriding molten pool geometry and nitrogen concentration profiles are broadly consistent with the experimental results for various laser intensities and nitrogen pressures. Due to the combined driving of both concentration and temperature gradient, a rapid increase of nitrogen concentration profile during the heating stage is observed. While in the cooling stage, the redistribution of nitrogen in substrate and the local maximum of nitrogen close to the surface are mainly caused by the transient temperature gradient which is confirmed by both the experimental and simulated results. In addition, the influence of laser intensity on nitrogen transport is strongly related to the initial nitrogen concentration at surface. Especially, when the initial nitrogen concentration at surface approaches to the maximum concentration limit of nitrogen in titanium nitrided layer, slight drops of nitrogen concentration in molten zone are observed with the increase of laser intensity. This indicates that the earlier formed diffusion barrier due to the maximum concentration limit will impede the further penetration of atomic nitrogen and thus lead to the relatively lower concentration.