Interaction Of Laser Beam Research Articles

Interaction of Laser beam, Powder Stream and Molten Pool in Laser Deposition Processing with Coaxial Nozzle

Powder-based laser deposition technology has widely used for parts coating, repairing and additive manufacturing. The quality and efficiency of laser deposition largely depends on the powder stream controlling. For some special laser deposition processing, such as ultra-high-speed laser cladding, inside laser cladding, FGM(Functionally Graded Materials) and MMC(Metal Matrix Composite) coating or parts manufacturing, the power stream controlling become more complex, because the powder melting behaviour is changed and varying proportion mix powder is used. In order to achieve the best feeding properties and highest powder efficiency aiming to different application requirement, the optimization of the nozzle geometry and controlling of powder flow are quite necessary. For this purpose, a comprehensive numerical model is developed to study the powder flow of coaxial nozzles, which include powder stream spatial distribution, flow rate, and trajectory. The powder stream convergence characteristics for different laser deposition application, and the interaction between laser beam, powder stream and molten pool are studied by numerical and experimental methods. The nozzle geometries, powder properties, and shield gas setting are optimized based on the understanding of the powder concentration distribution.

Making pions with laser light

The interaction of high intensity short pulse laser beams with plasmas can accelerate electrons to energies in excess of a GeV. These electron beams can subsequently be used to generate short-lived particles such as positrons, muons, and pions. In recent experiments, we have made the first measurements of pion production using ‘all optical’ methods. In particular, we have demonstrated that the interaction of bremsstrahlung generated by laser driven electron beams with aluminum atoms can produce the long lived isotope of magnesium (27Mg) which is a signature for pion (π+) production and subsequent muon decay. Using a 300 TW laser pulse, we have measured the generation of 150 ± 50 pions per shot. We also show that the energetic electron beam is a source of an intense, highly directional neutron beam resulting from (γ, n) reactions which contributes to the 27Mg measurement as background via the (n, p) process.

Laser surface texturing of Ti6Al4V alloy, stainless steel and aluminium silicon alloy

In the present work a theoretical and experimental study of laser beam interactions was conducted during the laser texturing with number of metallic materials including Ti6Al4V alloy, nickel free austenitic steel (316L) and aluminium silicon alloy (AlSi7). The surface texturing experiment was carried out using a picosecond and nanosecond lasers. The texturing was performed using various power radiation density of laser’s impulses that were absorbed by the surface of the textured materials. The microstructure and surface topography was characterised by SEM. The optical reflectance for Ti6Al4V, 316L and AlSi surfaces after laser texturing decreased. In the performed experiment it was possible to control for the surface’s optical reflectance of Ti6Al4V, 316L and AlSi7 from its original value to value near zero. The surface AlSi7 and Ti6Al4V after texturing with picoseconds laser did not show an intense decrease in corrosion resistance. The corrosion resistance of 316L in Ringer solution after laser texturing with high power density of laser radiation dropped significantly.

Finite Element Analysis of Interaction of Laser Beam with Material in Laser Metal Powder Bed Fusion Process.

A deep understanding of the laser-material interaction mechanism, characterized by laser absorption, is very important in simulating the laser metal powder bed fusion (PBF) process. This is because the laser absorption of material affects the temperature distribution, which influences the thermal stress development and the final quality of parts. In this paper, a three-dimensional finite element analysis model of heat transfer taking into account the effect of material state and phase changes on laser absorption is presented to gain insight into the absorption mechanism, and the evolution of instantaneous absorptance in the laser metal PBF process. The results showed that the instantaneous absorptance was significantly affected by the time of laser radiation, as well as process parameters, such as hatch space, scanning velocity, and laser power, which were consistent with the experiment-based findings. The applicability of this model to temperature simulation was demonstrated by a comparative study, wherein the peak temperature in fusion process was simulated in two scenarios, with and without considering the effect of material state and phase changes on laser absorption, and the simulated results in the two scenarios were then compared with experimental data respectively.

Terahertz radiation generation through the nonlinear interaction of Hermite and Laguerre Gaussian laser beams with collisional plasma: Field profile optimization

The nonlinear interaction of Hermite-Gaussian and Laguerre-Gaussian (LG) laser beams with a collisional inhomogeneous plasma is studied, and the amplitude of the emitted terahertz (THz) electric field is evaluated. The effects of laser beams and plasma parameters, including the beams width, LG modes, the plasma collision frequency, and the amplitude of density ripple on the evolution of THz electric field amplitude, are examined. It is found that the shape of the generated THz radiation pattern can be tuned by the laser parameters. In addition, the optimum values of the effective parameters for achieving the maximum THz electric field amplitude are proposed. It is shown that a significant enhancement up to 4.5% can be obtained in our scheme, which is much greater than the maximum efficiency obtained for laser beams with the same profiles.

Interaction of laser beams with magnetized substance in a strong magnetic field

Laser-driven magneto-inertial fusion assumed plasma and magnetic flux compression by quasisymmetric laser-driven implosion of magnetized target. We develop a 2D radiation magnetohydrodynamic code and a formulation for the one-fluid two-temperature equations for simulating compressible non-equilibrium magnetized target plasma. Laser system with pulse radiation with 10 ns duration is considered for numerical experiments. A numerical study of a scheme of magnetized laser-driven implosion in the external magnetic field is carried out.

Flower-like silver nanocrystals: facile synthesis via a gas–solution interface technique

In this paper, flower-like Ag nanocrystals and their fractal networks were successfully synthesized by gas–solution interface technique at the surface of AgNO3 water solution with the assistance of ammonium citrate and of gaseous N2H4 used as reductant. The synthesized flower-like silver structure consisted of a large number of petal-like silver nanoplates. They were characterized by scanning and transmission electron microscopy, absorption UV–Vis spectroscopy, and X-ray diffraction. In addition to the standard silver fcc modification, the nanostructures contained the hexagonal polymorph (4H-Ag) in the amount of about 5%. The effect of pH of the solution on the morphology of nanoparticles and on the silver crystal structure was examined. Depending on the time of treatment with gaseous hydrazine, it was possible to obtain either separate flower-like nanoparicles and their fractal networks, or continuous films formed by rather closely packed petal-like nanoparticles. The surface-enhanced Raman scattering effect was observed, and the most intense interaction of laser beam with the silver nanoparticles occurred when the solution side of the synthesized film was irradiated.

Turning point temperature of self-focusing at laser–plasma interaction with weak relativistic-ponderomotive nonlinearity: effect of light absorption

In this communication, we have examined the influence of light absorption on turning point temperature of self-focusing in the interaction of Gaussian laser beam in plasma. The dielectric function of plasma introduced herein is under weak relativistic and ponderomotive regime. Differential equation for beam-width parameter has been established by using parabolic equation approach under WKB and paraxial approximations. Numerical analysis shows that light absorption plays an important role on turning point temperature of self-focusing under relativistic and ponderomotive regime. It is also found that variation of normalized plasma density, normalized laser intensity parameter and plasma dielectric function with dimensionless distance of propagation gives reasonably interesting results.

Alternative irradiation schemes for NIF and LMJ hohlraums

We explore two alternative irradiation schemes for the large (‘outer’) and small (‘inner’) angle beams that currently illuminate National Ignition Facility (NIF) and Laser Mégajoule cavities. In the first, while the outer laser beams enter through the usual end laser entrance holes (LEH), the inner beams enter through slots along the cavity axis wall, illuminating the back wall of the cavity. This avoids the current interaction of the inner laser beams with the gold wall bubbles generated by the outer beams, which leads to large time-dependent changes in drive symmetry. Another scheme potentially useful for NIF uses only the outer beams. The radiative losses through the slots or from the use of outer beams only are compensated by using a smaller cavity and LEH.

A new method for isolating plasma interactions from those of the laser beam during plasma nitriding

A new method for separating the interactions of a laser plasma from those of a laser beam with a titanium substrate was developed. A laser-sustained plasma (LSP) was generated by striking the plasma on a titanium plate in a flowing nitrogen atmosphere at ambient pressure and subsequently removing the strike plate. The resultant nitrogen plasma was sustained indefinitely around the laser focal plane until the nitrogen gas flow and/or the laser power were switched off. The laser-sustained nitrogen plasma was then used as a “reactor” to study the effects of a nitrogen plasma, independent of the laser beam, when the plasma was brought into close proximity, (2 to 3mm), parallel to a titanium substrate. There was no interaction of the parallel laser beam with the substrate. Heat, nitrogen and titanium were exchanged between the nitrogen LSP and substrate resulting in melting, nucleation and growth of faceted and dendritic TiN crystals, rectangular hollow TiN morphologies and particulate TiN deposits. Dense TiN layers up to 300μm thick formed within 5s. The results demonstrated that compositionally graded layers of nitrogen-enriched titanium, and titanium nitride could be formed very rapidly on model, commercially-pure titanium substrates, with promise for extension to commercial alloys such as Ti-6Al-4V.

Fly-ash contribution to Nd:YAG laser yellowing and its mitigation using UV-B light

Abstract Nd:YAG Q-Switched laser cleaning of soiled stone at 1064 nm can sometimes result in yellower appearances than other conventional cleaning techniques. The yellowing effect is known to be at least partially due to the laser beam interaction with soiling matter, especially with infra-red absorbing components such as iron oxides, carbonaceous particles or fly-ash. In this study, pure plaster plates were artificially soiled with natural black crust and fly-ash powders. The morphology and crystalline structure of the soiling materials was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Soiled plaster plates were then treated by Nd:YAG QS laser light at 1064 nm. The laser irradiation led to the appearance of a yellow tone in all cases, highlighting the fly-ash contribution to the yellowing effect. Afterwards, the irradiated plaster plates were exposed to UV-B light (313 nm) for a few dozen hours using an accelerated UV ageing chamber. This treatment resulted in a significant attenuation of the yellow colour for all the samples. Colour measurements revealed that this photo-bleaching effect was essentially due to brightness L* and saturation C* variations and not to hue h* variation towards less yellow shades. As hue variation is often related to chemical transformations of chromophores, this result tends to indicate that the yellowing reduction was mainly due to scattering effects.

Investigation of Weakly Relativistic Ponderomotive Effects on Self-Focusing During Interaction of High Power Elliptical Laser Beam with Plasma

This paper presents an investigation of weakly relativistic ponderomotive effects on self-focusing during interaction of high power elliptical laser beam with plasma. The nonlinear differential equations for the beam width parameters of elliptical laser beam have set up by using Wentzal–Krammers–Brillouin (WKB) and paraxial approximations. These equations have been solved numerically by using fourth order Runge–Kutta method to study the variation of these beam width parameters against normalized distance of propagation. Effects of variation in laser beam intensity, plasma density and electron temperature on the beam width parameters are also analyzed.

Ultraviolet-Diode Pump Solid State Laser Removal of Titanium Aluminium Nitride Coating from Tungsten Carbide Substrate

This paper presents an investigation on the titanium aluminium nitride (TiAlN) coating removal from tungsten carbide (WC-Co) substrate using a diode pump solid state (DPSS) ultraviolet (UV) laser with maximum average power of 90 W, wavelength of 355 nm and pulse width of 50 ns. The TiAlN coating of 1.5 μm thickness is removed from the WC-Co substrate with laser fluence of 2.71 J/cm2 at 285.6 number of pulses (NOP) and with NOP of 117.6 at 3.38 J/cm2 fluence. Titanium oxide formation was observed on the ablated surface due to the re-deposition of ablated titanium residue and also attributed to the high temperature observed during the laser ablation process. Crack width of around 0.2 μm was observed over both TiAlN coating and WC-Co substrate. The crack depth ranging from 1 to 10 μm was observed and is related to the thickness of the melted carbide. The crack formation is a result of the thermal induced stresses caused by the laser beam interaction with the material as well as the higher thermal conductivity of cobalt compared to WC. Two cleaning regions are observed and is a consequence of the Gaussian distribution of the laser beam energy. The surface roughness of the ablated WC-Co increased with increasing laser fluence and NOP.

Influence of sense rotation of circularly polarized laser pulse on the wake-field acceleration in magnetized plasma

The present paper investigates the effect of different sense rotations of circularly polarized (CP) Gaussian laser pulse on wake-field generation and electron acceleration when there is an axial static magnetic field. The nonlinear equation, which explains the interaction of intense CP laser beam with magnetized plasma in the quasi static approximation, is derived. The numerical analysis of our results indicates that the amplitude of plasma wake for both sense of circular polarization is similar, but affected by propagation direction of exterior magnetic field. It is found that the dephasing length is increased for the left-hand polarized laser fields, while decreased for the right-hand ones, which is reinforced as the enhancement of the forward exterior magnetic field. It is shown that the right-hand polarization laser pulse with reversed exterior magnetic field could leads to much larger electron energy (about 2.4GeV) than that of other cases.

Thermal interaction of multi-pulse laser beam with eye tissue during retinal photocoagulation: Analytical approach

The laser-induced temperature disturbance within retinal pigmented epithelium (RPE) and in the adjacent layers of a human eye is studied with the aim to specify laser optimal parameters providing safe treating. Proposed is a generalized model of a laser irradiated multi-layered media with arbitrary number of layers having uniform thermal and discrete optical properties. An analytical approach is used that allowed obtaining description of the spatial and temporal evolution of the temperature in the irradiated media. The required maximum temperature is kept as a preassigned value, and the search for necessary laser parameters is subjected to this condition. Calculations are made for Gaussian and uniform (top hat) lasers with wavelengths 514, 532 and 577nm. Necessary combinations of pulse power and its duration that provide predetermined peak temperature within RPE are identified. The possible inter-individual deviations of eye physical properties are reviewed and probable risks of RPE overheating arising from these uncertainties are evaluated for the first time. The advanced concept of sub-threshold multi-pulse laser treatment is analyzed. The method for definition of necessary pulse train parameters for maintaining the target RPE temperature at the end of the pulse train is proposed. Analytical model is validated in a wide range of laser parameters against state-of-the-art theoretical and experimental data available in the literature.

Laboratory reflectometer for the investigation of optical elements in a wavelength range of 5–50 nm: description and testing results

We describe a laboratory reflectometer developed at the IPM RAS for precision measurements of spectral and angular dependences of the reflection and transmission coefficients of optical elements in a wavelength range of 5–50 nm. The radiation is monochromatised using a high-resolution Czerny–Turner spectrometer with a plane diffraction grating and two spherical collimating mirrors. A toroidal mirror focuses the probe monochromatic beam on a sample. The X-ray source is a highly ionised plasma produced in the interaction of a high-power laser beam with a solid target at an intensity of 1011–1012 W cm–2. To stabilise the emission characteristics, the target executes translatory and rotary motions in such a way that every pulse irradiates a new spot. The short-focus lens is protected from contamination by erosion products with the use of a specially designed electromagnetic system. The samples under study are mounted on a goniometer is accommodated in a dedicated chamber, which provides five degrees of freedom for samples up to 500 mm in diameter and two degrees of freedom for a detector. The sample mass may range up to 10 kg. The X-ray radiation is recorded with a detector composed of a CsI photocathode and two microchannel plates. A similar detector monitors the probe beam intensity. The spectral reflectometer resolution is equal to 0.030 nm with the use of ruled gratings with a density of 900 lines mm–1 (spectral range: 5–20 nm) and to 0.067 nm for holographic gratings with a density of 400 lines mm–1 (spectral range: 10–50 nm). We analyse the contribution of higher diffraction orders to the probe signal intensity and the ways of taking it into account in the measurements. Examples are given which serve to illustrate the reflectometer application to the study of multilayer mirrors and filters.

Magnetic field effect on the self-focusing of an intense laser pulse interacting with a bulk medium of graphite nanoparticles

The motivation of the present work is the study of self-focusing of an intense laser beam propagating through a magnetized bulk medium consisting of metallic nanoparticles. Using a perturbative method, the wave equation describing the nonlinear interaction of the intense laser beam with metallic magnetized nanoparticles is derived. Evolution of the laser spot size for the circular polarization with the Gaussian profile is considered. A graphite nanoparticle medium is introduced as a good candidate for self-focusing of electromagnetic waves with the wavelength in the micrometer range where plasmon resonance occurs. In such a frequency area, using a few hundred Tesla external magnetic field can substantially improve the focusing property of the medium. The threshold power for self-focusing at least two orders of magnitude is less than that for the identical case of the plasma medium. In addition, a typical external magnetic field for improving the focusing property of the medium is much lower than other conventional nonlinear media like plasma.

Nonscanning Moiré deflectometry for measurement of nonlinear refractive index and absorption coefficient of liquids.

In this work, a nonscanning measurement technique is presented for determining the nonlinear refractive index and absorption coefficient of liquid media based on Moiré deflectometry. In the proposed method two lasers are used: a low power, wide beam as probe and a high power with specific wavelength as a pump. Interaction of the pump laser beam with the nonlinear sample changes the refractive index, which leads to change in convergence/divergence of the collimated incident probe laser beam. The induced deflection is monitored by Moiré deflectometry. If the pump laser has a Gaussian intensity profile, the refractive index profile of the sample is Gaussian, too. Measuring the deflection angle of the probe beam by Moiré fringes deflection, and by using the inverse Abel transform integral, the refractive index profile and nonlinear refractive index can be determined. This method is fast, easy, and insensitive to environmental noise and allows real-time measurement. Also, the refractive index profile of the interacted medium with pump laser can be achieved by this technique. As a liquid sample, a DCJ dye in water solution was studied. The value of nonlinear refractive index, n2, and absorption coefficient, α, were obtained -2.54×10-4 cm2 w-1 and 1.368 cm-1, respectively.

Modeling the ponderomotive interaction of high-power laser beams with collisional plasma: the FDTD-based approach.

The ponderomotive interaction of high-power laser beams with collisional plasma is modeled in the nonrelativistic regime and is simulated using the powerful finite-difference time-domain (FDTD) method for the first time in literature. The nonlinear and dissipative dielectric constant function of the collisional plasma is deduced that takes the ponderomotive effect into account and is implemented in the discrete framework of FDTD algorithms. Maclaurin series expansion approach is applied for implementing the obtained physical model and the time average of the square of light field is extracted by numerically evaluating an integral identity based on the composite trapezoidal rule for numerical integration. Two numerical examples corresponding to two different types of laser beams, Gaussian beam and vortex Laguerre-Gaussian beam, propagating in collisional plasma, are presented for specified laser and plasma parameters to verify the validity of the proposed FDTD-based approach. Simulation results show the anticipated self-focusing and attenuation phenomena of laser beams and the deformation of the spatial density distributions of electron plasma along the beam propagation path. Due to the flexibility of FDTD method in light beam excitation and accurate complex material modeling, the proposed approach has a wide application prospect in the study of the complex laser-plasma interactions in a small scale.

Optothermodynamic Method of Diagnosis of Absorption Coefficient in the Liquids

Optothermodynamic method of diagnosis of absorption coefficient of waves in inhomogeneous absorbing liquids has been developed temperature influence on wave’s absorption coefficient has been determined. Optothermodynamic method allows establishing relation between optic and thermophysical properties of liquid. Developed method is based on the application of energy conservation on the interaction of laser beams with inhomogeneous absorbing liquids.