Increasing Laser Energy Research Articles

Research on the conduction process of laser triggered vacuum switch

In this paper, the conduction process of the Laser Triggered Vacuum Switch (LTVS) is studied. First, the velocity, density, and temperature of the initial plasma in the LTVS are simulated using COMSOL Multiphysics software. It is found that the generation and development of the initial plasma are at the ns level. Second, the pre-breakdown current test circuit of the LTVS is established. It is found that when the applied voltage at both ends of the switch is 60 V, the multi-rod LTVS is successfully conducted, and then, the current becomes the conduction current and the voltage applied at both ends of the switch decreases significantly. Finally, the images of the LTVS vacuum arc are taken. With the increase in laser energy, the more abundant the initial plasma is, the lower the required gap voltage is. When the current increases to a certain value, the vacuum arc appears in multiple discharge channels, which makes the arc have a diffusion morphology. It is found that the current withstand capacity of a single channel is about 50 kA. As the multi-rod LTVS has three channels, its current withstand capacity can reach 150 kA.

Study on impulse and ablation of aluminum irradiated by millimeter spot of short pulse laser

Aluminum is a high performance working medium for laser ablation micro propulsion. In order to study the propulsion performance and ablation of aluminum under millimeter light spot irradiation, a short pulse Nd: YAG laser with wavelength of 1064nm and pulse width of 8NS was used to irradiate aluminum target in atmosphere. The impulse, the impulse coupling coefficient and the ablation morphology of the aluminum target produced by 6 kinds of millimeter-level light spots are measured. The experimental results show that when the spot diameter reaches 6-7mm, the increasing trend of impulse and impulse coupling coefficient of aluminum target with the increase of laser energy slows down; A large number of ablation products began to accumulate on the surface of the target pit.

Spectroscopic Diagnosis of the CdO:CoO Plasma Produced by Nd:YAG Laser

In this paper, the optical emission spectrum (OES) technique was used to analyze the spectrum resulting from the (CdO:CoO) plasma in air, produced by Nd:YAG laser with λ=1064 nm, τ=10 ns, a focal length of 10 cm, and a range of energy of 200-500 mJ. We identified laser-induced plasma parameters such as electron temperature (Te) using Boltzmann plot method, density of electron (ne), length of Debye (λD), frequency of plasma (fp), and number of Debye (ND), using two-Line-Ratio method. At a mixing ratio of X= 0.5, the (CdO:CoO) plasma spectrum was recorded for different energies. The results of plasma parameters caused by laser showed that, with the increase in laser energy, the values of Te, ne and fp were increased, while the value of λD was decreased. The calculated electron temperature value was in the range of 0.449-0.619 eV at ratio X=0.5

Study of Electrical Properties of Silver Nanoparticles on Porous Silicon

In this paper, porous silicon has been prepared and studied by photochemical etching method using a n-type silicon wafer with electrical resistivity (0.01-0.02 Ω.cm), orientation (100), hydrofluoric acid of 20% HF, current density of 15 mA / cm2 and etching time at (5 min). Silver nanoparticles (AgNPs) have been deposited using laser ablation by drop casting with different laser energy of 400,600 and 800m J. The electrical properties (I-V measurements) of silver nanoparticles on porous silicon have studied in both light and dark conditions. It can be seen the samples behave a rectifier and the current density increases with increase laser energy due to increase in concentration of silver nanoparticles, which lead to a decrease in the values of resistivity as the laser energy increases, this is attributed to the pores are filled with silver nanoparticles and lead to interference between silver and the porous silicon layer. The silver nanoparticles play an important role in forming a homogeneous layer and enhancing the crystal stability of the porous silicon layer.

Study on HfO 2 /SiO 2 high reflective film damage induced by 248nm UV excimer laser

The deep ultraviolet optical thin films play an important role in excimer lasers, deep ultraviolet lithography machine and other laser systems. In this paper, the experiment on damage in HfO2/ SiO2 high reflective film irradiated by 248nm ultraviolet excimer laser was carried out. And the high reflection film is coated with a layer of SiO2 as a protective film. The damage morphology and depth of the samples were observed and analyzed by means of DIC microscope and surface profiler system. In this experiment, the laser-induced damage threshold of HfO2/ SiO2 high reflective film coated with SiO2 protective film was calculated by zero damage probability. Based on the surface characteristics of the damage points, we established the model to analyze the damage mechanism of the high reflectance film by using Finite Element Method(FEM). The experimental results show that the damage threshold of 248nm excimer laser to the highly reflective film is 3.086J/cm2. When the incident laser energy is 3.33J/cm2, stress damage appears on the surface of the highly reflective film. With the increase of laser energy, the high reflective film will appear melting damage and corrugated damage.

Pulsed laser deposition of nanostructured HgI2 on Si substrate for photodetector application

Nanostructured mercury iodide (HgI2) films were deposited on glass and silicon substrates by Nd:YAG laser deposition technique. The structural, optical and electrical properties of HgI2 films deposited at two laser energy densities of 5.1 and 6.3 J/cm2 were studied. The structural studies show that the deposited films are crystalline in nature with tetragonal phase and the film grown at 5.1 J/cm2 was highly oriented along (002) plane, whereas the film deposited at 6.3 J/cm2 was highly oriented along (114). Scanning electron microscope (SEM) investigations reveal that the film prepared at 5.1 J/cm2 has morphology of spherical nanograins and converted to nanorods morphology as laser energy density increases to 6.3 J/cm2. Energy dispersive x-ray (EDX) data confirmed that the atomic ratio of the [Hg]/[I] increases with increasing laser energy density. The optical properties showed that the optical energy gap of the films prepared at 5.1 and 6.3 J/cm2 were 3.72eV and 4eV, respectively. The electrical resistivity of the films deposited at 5.1 and 6.3 J/cm2 was found to be 8.3 × 108 and 1.03 × 109 Ω cm, respectively. The best properties of the film and the device were obtained for film deposited at laser energy density near the calculated threshold energy density. The photodetection properties of n-HgI2/p-Si heterojunction photodetector showed that the maximum responsivity of the photodetector was 0.34AW-1 at 410 nm. The effect of laser energy density on the quantum efficiency and specific detectivity of the HgI2/p-Si photodetectors was studied. The band lineup of n-HgI2/p-Si was constructed under illumination.

Numerical Study of Nanosecond Pulsed Laser Impact on a Water Droplet

An integrated hydrodynamic model that involves a laser heat source, surface evaporation, and interfacial driving forces is developed to simulate the complex physical process of a nanosecond pulsed laser impacting on a water droplet. Droplet deformation tracked by the coupled level set and volume of fluid method is contrasted with the experimental results, and it is shown that the coupled model can be used to simulate the droplet expansion dynamics. From the simulation of droplet deformation, it can be found that, with increasing laser energy, the droplet becomes thinner. With the highest laser energy, the jet on the opposite side to laser impact is interpreted as the flow of high-speed fluid near the axis, which is also confirmed by the velocity field. The simulated temperature reaches or even exceeds the critical value, and the recoil pressure does not completely cover the whole hemispherical surface of the droplet. The liquid-removal depth, which represents the distance that the liquid-phase interface retreats during evaporation, is much shallower than the absorption depth. It can be concluded that propulsion is gained from the intense evaporation of the superheated layer.

Influence of Laser Energy on the Structural and Optical Properties of (CdO):(CoO) Thin Films Produced by Laser-Induced Plasma (LIP)

In this work, (CdO)1-x (CoO)x thin films were prepared on glass slides by laser-induced plasma using Nd:YAG laser with (λ=1064 nm) and duration (9 ns) at different laser energies (200-500 mJ) with ratio (x=0.5), The influence of laser energy on structural and optical properties has been studied. XRD patterns show the films have a structure of polycrystalline wurtzite. As for AFM tests results for the topography of the surface of the film, where the results showed that the grain size and the average roughness increase with increasing laser energy. The optical properties of all films were also studied and the results showed that the absorption coefficient for within the wavelength range (280-1100 nm), The value of the optical power gap for direct transitions was shown to be reduced by increasing laser energy within the range (4.29-3.7 eV).

Improve the binding force of PEEK coating with Mg surface by femtosecond lasers induced micro/nanostructures

A polymer coating is an effective approach to increase the surface wear and corrosion resistance of magnesium alloys, but the low bonding strength limits its further applications. In this study, poly-ether-ether-ketone (PEEK) coating was prepared on the AZ31 magnesium alloy. Femtosecond laser surface treatment was used to change the surface characteristics of Mg-base alloy, and the effect of the laser-induced structures on improving the bonding strength of PEEK coating was investigated. With the increase in laser energy, the gap between laser-induced nanostructures gradually increases. When V = 1000 mm s−1, a uniform striped structure is formed on the surface, and the average period is about 0.5 μm. When V = 300 mm s−1, the stripe breaks and grows in the length direction, and the surface texture tends to be a coral-like structure with diameter of about 7 μm. When the scanning speed is reduced to V = 200 mm s−1, the grooves gradually deepen, and irregular bumped structures were formed with the spacing of about 3 ~ 5 μm. The surface roughness after laser treatment increased from 9.37 nm to 589.3 nm, and the surface of magnesium alloy changed from hydrophilic to hydrophobic. PEEK coating was prepared by electrostatic spraying. The raw PEEK is fully melted and infiltrated with the laser-induced structure matrix, resulting in a high bonding strength compared with the untreated Mg matrix. The surface of the nanostructure has excellent wettability to PEEK coating, which improves the adhesion of coating and prolongs the service life of the magnesium alloy. PEEK coating has excellent sealing effect and chemical corrosion resistance, which increases the corrosion potential on the substrate surface and the corrosion resistance. Results can provide a new approach to improve the bonding properties between metal bases and polymer coating.

CO2 laser polishing of laser-powder bed fusion produced AlSi10Mg parts

Poor surface quality represents an important issue that needs improvement for metal Additively Manufactured parts. Both short or long wavelength lasers have been applied for surface polishing in order to improve the surface finish. In this work, the possible use of a CO 2 laser for the surface polishing of AlSi10Mg parts made by Laser-based Powder Bed Fusion (L-PBF) was explored. The high surface roughness in the as-built condition can lead to increased laser energy absorption. In order to assess the effects of the main laser-related process parameters, the experiments were carried out on L-PBF samples built vertically with respect to the build platform. Their effect on the surface were evaluated by means of the surface arithmetical mean height (S a ), surface skewness (S sk ) and primary profile root mean square slope (P dq ), obtained via confocal microscopy . Microstructure evolution was also investigated by means of SEM and EDS analysis. The results showed a large reduction in surface roughness, ranging from the 67% to the 85% of the starting value. Microstructure of the re-molten layer revealed an increased grain size and an increased Si content that led to an overall hardness increase from 85 to 121 HV. • A CO 2 laser was used to perform surface re-melting of AlSi10Mg L-PBF samples. • The surface roughness (S a ) was reduced up to the 85%. • Surface symmetry, analyzed by means of areal skewness (S sk ), was improved. • Profile root mean square slope (P dq ) was also evaluated and reduced up to the 90%. • Vickers microhardness increased up to the 30% in the polished area.

Hybrid x-ray laser-plasma/laser-synchrotron facility for pump-probe studies of the extreme state of matter at NRC "Kurchatov Institute".

We developed a hybrid optical pump-x-ray probe facility based on the "Kurchatov's synchrotron radiation source" and terawatt (TW) femtosecond laser. The bright x-ray photon source is based on either synchrotron radiation [up to 6 × 1014 photons/(s mm2 mrad2 0.1% bandwidth)] or laser-plasma generators (up to 108 photons/sr/pulse). The terawatt (TW) femtosecond laser pulse initiated phase transitions and a non-stationary "extreme" state of matter, while the delayed x-ray pulse acts as a probe. The synchronization between synchrotron radiation and laser pulses is achieved at 60.3MHz using an intelligent field-programmable gate array-based phased locked loop. The timing jitter of the system is less than 30ps. In laser-plasma sources, the x-ray and laser pulses are automatically synchronized because they are produced by using the same laser source (TW laser system). We have reached an x-ray yield of about 106 photons/sr/pulse with 6-mJ sub-ps laser pulses and using helium as a local gas medium. Under vacuum conditions, the laser energy increase up to 40 mJ leads to the enhancement of the x-ray yield of up to 108 photons/sr/pulse. The developed hybrid facility paves the way for a new class of time-resolved x-ray optical pump-probe experiments in the time interval from femtoseconds to microseconds and the energy spectrum from 3 to 30 keV.

The acceleration mechanism of shock wave induced by millisecond-nanosecond combined-pulse laser on silicon

The velocity variation law of shock wave induced by millisecond-nanosecond combined-pulse laser has been investigated experimentally. The pulse delay and laser energy are important experimental variables. The method of laser shadowgraphy is used in the experiment. Experimental results show that when the pulse delay is 2.4 ms, the ms and ns laser energy density is 301 J cm−2 and 12 J cm−2, respectively, the velocity of shock wave is 1.09 times faster than that induced by single ns pulse laser. It is inferred that the shock wave propagates in the plasma is faster than that in air. When the ms and ns laser energy density is 414.58 and 24 J cm−2, the velocity of shock wave shows rising trend with pulse delay in a range of 1.4 ms > Δt > 0.8 ms. It is indicated that with the increase of ns laser energy, the laser energy absorbed by laser-supported absorption wave increases. The mechanism of inverse bremsstrahlung absorption acts with target surface absorption simultaneously during the ns laser irradiation. Thus, the phenomenon of the double shock wave is induced. The numerical results of the phenomenon were accordance with experiment. The results of this research can provide a reference for the field of laser propulsion.

Effect of laser shock peening and carbonitriding on tribological properties of 20Cr2Mn2Mo steel alloy under dry sliding conditions

In this study, the effect of laser shock peening and low-temperature vacuum carbonitriding on the tribological properties of 20Cr2Mn2Mo steel alloy was investigated. The original sample and samples treated by laser shock peening with different laser energy and number of impacts were carbonitrided in vacuum at 760 °C. The effect of laser shock peening parameters on surface roughness, microhardness, coefficient of friction, and wear properties was studied. The results indicated that the surface roughness and microhardness increase with respect to laser energy and number of impacts. For exceedingly high laser energy or number of impacts, the coefficient of friction evidently increases. Furthermore, laser shock peening and carbonitriding lead to high-density dislocations and second-phase particles. With increasing laser energy and number of impacts, the primary wear mechanism changes from abrasive wear to a mix of abrasive and adhesive wear.

Numerical studies of dielectric material modifications by a femtosecond Bessel–Gauss laser beam

Femtosecond Bessel–Gauss beams are attractive tools to a large area of laser processes including high aspect ratio volume nanostructuration in dielectric materials. Understanding the dielectric material response to femtosecond Bessel–Gauss beam irradiation is key in controlling its modifications and designing new structures. In this work, we show how the material ionization affects the propagation of the femtosecond Bessel–Gauss laser beam and can limit the laser energy deposition. By performing 2D/3D numerical simulations, we evaluate the absorbed laser energy and subsequent material modifications. First, we model the electron dynamics in the material coupled to the 3D laser propagation effects. Then, we consider 2D thermo-elasto-plastic simulations to characterize the medium modifications. Results show that the laser ionized matter induces a screening of the incident gaussian beams which form the Bessel-Gauss beam. This effect leads to a limitation of the maximum laser energy deposition even if the incident laser energy increases. It can be reduced if a tigthly focused femtosecond Bessel–Gauss beam is used as the angular aperture of the cone along which the incident gaussian beams are distributed is larger.

Simultaneous Optimization of Laser Energy and Coating Thickness in Surface Alloying of Al with Fe

In the two-step deposition technique of the laser surface alloying process, the alloying elements are introduced onto the bulk material’s surface. In such process, two main parameters determine the alloying quality: the thickness of the coating and the laser energy supplied onto the specimen. In this work, the laser surface alloying of aluminium (Al) with iron (Fe) is carried out by optimizing both parameters. This is accomplished by assessing the improvement in the hardness after laser treatment. In general, the thicker coating desires higher laser energy to cause surface melting and sequentially diffusion of Fe into molten Al to occur. This is indicated by the linear relationship between the thicknesses for the peak hardness value with the laser energy whereby the optimum energy shifted to higher energy for a thicker coating. The increase in laser energy increases Fe particle’s chance to migrate via diffusion into the bulk Al substrate. However, at 140μm the optimized energy reaches a peak value at 455mJ which is the maximum energy to be supplied in this process before the coating is lost due to excessive ablation. For thicker coatings, the laser’s action does not penetrate enough onto the substrate to cause sufficient melting of the Al surface for alloy formation. The maximum hardness obtained was 40.8 HV at the optimum condition for 140μm thickness treated with 455 mJ. The formation of an alloyed compound is further confirmed by x-ray diffraction technique whereby compounds such as AlFe, Al13Fe4, and AlFe6Si are present in the treated specimens.

B20-type FeGe on Ge(1 0 0) prepared by pulsed laser melting

B20-type FeGe is one of the noncentrosymmetric materials hosting magnetic skymions. In this work, we have prepared B20-type FeGe films by pulsed laser melting of metal Fe deposited on Ge(100). The formation of the B20 phase is confirmed by X-ray diffraction. The FeGe samples show a superparamagnetic behavior and their blocking temperatures increase with increasing the pulsed laser energy density. We conclude that this phenomenon is due to the increased grain size of the B20-type FeGe with increasing laser energy density. The presented method can be used to obtain different B20-type transition metal germanides and silicides, which can be magnetic skyrmion-hosting materials for spintronics.

Time and space-resolved laser-induced breakdown spectroscopy on molybdenum in air

In the present work, laser-induced plasma (LIP) of Mo is studied using both time and space resolved laser-induced breakdown spectroscopy (LIBS) in air as a function of incident laser energy. For this a second harmonic Q-switched Nd:YAG laser having pulse width of 7 ns and repetition rate of 1 Hz is used. The Boltzmann plot method is employed to estimate the plasma temperature of LIP using MoI and MoII lines separately. The stark-broadened profile of MoI-313.2 nm is exploited to measure the electron density. The temporal study in the time delay range of 0.5–5.0 μs shows that both the parameters, decay with the increase in delay time but increases with the increase in laser energy. It is observed that the plasma temperature estimated for MoII lines is higher than that of the MoI lines during the initial stage of plasma formation, delay time of 0.5–1.0 μs, but at a later time scale, both these species are found to possess nearly the same values of the temperature, indicating the coexistence of thermal equilibrium among the Mo atoms and ions in LIP. Therefore, in the second part of the experiment, time-integrated spatial evolution of the LIP of Mo is studied at a fixed delay of 2 μs as a function of axial distance normal to the target. It is found that emission intensity (MoI and MoII both), plasma temperature, and electron density initially increase with the increase in distance from the target, attains maximum value and then falls down. The Mc-Whirter criteria is applied to test the validity of local thermodynamic equilibrium (LTE). The relaxation time and diffusion length are estimated in time and space resolved studies respectively to take care of the transient and inhomogeneous nature of the LIP. The optical thin condition of LIP is verified by employing the branching ratio method. From these studies, a suitable spatio-temporal is identified where the LTE and optically thin plasma condition hold along with a high signal to noise ratio.

Characterization of Silver Nanoparticles on Porous silicon by Laser ablation in Liquid

In this article, Porous silicon was prepared using a photo-electrochemical etching method of n-type silicon at etching times (5 and 15 min.). The silver nanoparticles were coated on porous silicon by laser ablation in liquid with energy 400, 600, and 800 mJ. Atomic force microscope images showed an increase of pores size with etching time and it becomes smaller in diameter after laser ablation. Moreover, Scanning electron microscope displayed an aggregates formation when increasing laser energy. The strong peak of absorption of AgNPs found around 415-420 nm. The absorption amplitude increased when laser energy increases. Therefore, the nanostructures on the porous silicon properties play a crucial role in the formation of the homogeneity and this improves the structural stability of PSi layer.

An Analytical Model for Estimating the Bending Curvatures of Metal Sheets in Laser Peen Forming.

Laser peen forming (LPF) is suitable for shaping sheet metals without the requirement for die/mold and without causing high temperatures. An analytical model for estimating the bending curvatures of LPF is convenient and necessary for better understanding of the physical processes involved. In this paper, we describe a new analytical model based on internal force balance and the energy transformation in LPF. Experiments on 2024 aluminum alloy sheets of 1–3 mm thickness were performed to validate the analytical model. The results showed that for 1 mm and 3 mm thick–thin plates, the curvature obtained by the analytical model changes from −14 × 10−4 mm−1 and −1 × 10−4 mm−1 to 55 × 10−4 mm−1 and −21 × 10−4 mm−1, respectively, with the increase of laser energy, which is consistent with the experimental trend. So, when either the stress gradient mechanism (SGM) or the shock bending mechanism (SBM) overwhelmingly dominated the forming process, the analytical model could give relatively accurate predicted curvatures compared with the experimental data. Under those conditions where SGM and SBM were comparable, the accuracy of the model was low, because of the complex stress distributions within the material, and the complex energy coupling process under these conditions.

High-energy laser effects on carbon fiber reinforced polymer composites with a focus on perforation time

Commercially available carbon fiber reinforced polymer matrix composite panels (Hexply® M18-1/G939 and 8552/IM7) with different thicknesses (1-6 mm) were exposed to continuous-wave high-energy laser radiation at various laser powers up to 10 kW under static conditions. The perforation times, the size of the damaged volume and the residual compressive strengths are determined and correlated to the irradiation parameters. It is found that for the time of perforation, the damaged volume, which is approximated by a cylinder shaped model, correlates linearly with the laser energy imposed onto the sample surface. This relationship can be used for a prediction of the perforation time for various laser powers, material thicknesses and laser spot diameters. Increasing laser energy results in a decay of residual compressive strength after impact. Visual inspection as well as micro-focused computed X-ray tomography and scanning electron microscopy indicate a small area of thermal damage outside the laser spot. Additionally, infrared spectroscopy characterizes incipient heat damage most sensitively.