Wave Laser Irradiation Research Articles

Properties of a continuous optical discharge sustained by short-wave infrared laser radiation in high pressure argon

Abstract The paper is devoted to the experimental study of the characteristics of continuous optical discharge (COD) sustained by high power continuous wave laser radiation at a wavelength λ = 1.08 μm in high pressure argon. New data on COD threshold laser power dependence on argon pressure in the range 20-50 bar are obtained. COD threshold laser power is shown to be in good agreement with the data obtained by other authors and theoretical evaluations provided the contribution of plasma energy loss due thermal radiation is taken into account properly. A study of the convective plume oscillations around COD in argon has been carried out. It was found that in a pressure range 25-35 bar the growth of the laser radiation power leads to a decrease in convection oscillation frequency from 33 to 29 Hz, while the radius of the convective plume grows accordingly. The oscillation frequency ν and characteristic radius of the convective plume r0 were found to obey the similarity relation previously established in experiments with COD in xenon.

Photoluminescence of CaGa2S4: Nd, Yb compound at room temperature

In this paper, CaGa2S4:3%Nd,5%Yb; CaGa2S4:5%Yb; CaGa2S4:3%Nd compounds were synthesized, and their photoluminescence (PL) spectra, PL excitation (PLE) spectra and PL decay properties were studied at room temperature under one-photon and multi-photon excitation in a wide range of excitation intensities. The synthesis of the CaGa2S4 compound was carried out by a solid-phase reaction of a stoichiometric mixture of CaS and Ga2S3 powders in a quartz ampoule. Yb and Nd doping was carried out during the synthesis process using YbF3 and NdF3. PLE spectra were studied in the wavelength range from 250 to 850 nm, and PL spectra in the range of 400–1500 nm. It has been shown that after introducing Yb3+ ions into thiogallate crystals with Nd3+ ions, a new band near 488 nm is formed and the PL intensity increases by 1–2 orders of magnitude. The anti-Stokes PL spectra of CaGa2S4: Nd, Yb crystals in the visible region of the spectrum (400–700 nm) were studied when excited by continuous wave laser radiation with a wavelength of 975 nm. The kinetics of PL decay of all types of compounds at different wavelengths of single- and multi-photon excitation were determined. Depending on the PLE conditions, wavelength and intensity of the exciting radiation, monoexponential and non-monoexponential decay kinetics were observed with decay times in the range of 20–90 μs. Possible mechanisms of PLE and PL of CaGa2S4 crystals doped with neodymium and ytterbium ions are discussed.

Ignition of Anthracite Microparticles by Continuous Wave Laser Radiation with Wavelengths of 450 and 808 nm

Ignition of Anthracite Microparticles by Continuous Wave Laser Radiation with Wavelengths of 450 and 808 nm

Therapeutic potential of photobiomodulation on hydrogen peroxide‐induced oxidative damage in retinal pigment epithelial cells

Aims/Purpose: Photobiomodulation (PBM) is a cutting‐edge therapeutic method for restoring the functioning of injured mitochondria in experimental settings. Our goal was to find out how 780 nm PBM therapy affected the apoptosis and cell survival of hydrogen peroxide‐treated retinal pigment epithelial cells.Methods: After being treated with 150 μM hydrogen peroxide for 24 h, the retinal pigment epithelial (RPE) cells were exposed to continuous wave laser radiation with the following parameters: wavelength of 780 nm, power density of 140 mW/cm2, 65 mW/cm2 and 40 mW/cm2 and duration of 10 min and 30 min. Furthermore, light therapy was given to untreated control cells to check PBM effect on healthy group. After PBM therapy in a time‐dependent manner, cell survival and apoptosis were assessed by MTT assay and Annexin V/PI staining, respectively.Results: Based on MTT findings, PBM showed no obvious effect on cell viability in H2O2‐treated RPE cells, while after 48 h post‐PBM incubation, cell viability was dramatically improved. It was significantly increased at the power density of 140 mW/cm2 for 30 min application without unacceptable effect on control cells. RPE apoptosis was strikingly decreased in post‐PBM incubation group compared to H2O2‐treated group in a time‐dependent manner, as detected by flow cytometry.Conclusions: As a result, photobiomodulation supported its potential utility in the prevention and treatment of retinal disorders associated with oxidative stress by promoting cell survival and reducing apoptosis under oxidative stress.

Evolution of Surface Topography and Microstructure in Laser Polishing of Cold Work Steel 1.2379 (AISI D2) Using Quadratic, Top-Hat Shaped Intensity Distributions.

Within the scope of this study, basic experimental research was carried out on macro-laser polishing of tool steel 1.2379 (D2) using a square intensity distribution and continuous wave laser radiation. The influence of the individual process parameters on surface topography was analyzed by a systematic investigation of a wide range of process parameters for two different, square laser beam diameters. Contrary to a typical laser polishing approach, it was shown that short interaction times (high scanning velocity and small laser beam dimensions) are required to reduce both micro-roughness and meso-roughness. A significant reduction of surface roughness of approx. 46% was achieved from Raini = 0.33 ± 0.026 µm to Ramin = 0.163 ± 0.018 µm using a focused square laser beam with an edge length of dL,E = 100 µm at a scanning velocity of vscan = 200 mm/s, a laser power PL = 60 W and n = 2 passes. However, characteristic surface features occur during laser polishing and are a direct consequence of the laser polishing process. Martensite needles in the micro-roughness region, undercuts in the meso-roughness region, and surface waviness in the macro-roughness region can dominate different regions of the resulting surface roughness spectrum. In terms of mechanical properties, average surface hardness was determined by hundreds of nano-indentation measurements and was approx. 390 ± 21 HV0.1 and particularly homogeneous over the whole laser polished surface.

Influence of temporal pulse-shaping on laser surface texturing of metals using fast modulated cw-fiber laser radiation

Remote ablation cutting with continuous wave laser radiation is a process commonly used for the surface pretreatment of large area metallic parts before joining of metal-polymer hybrid structures, due to their cost-effectiveness and high average powers when compared to short-pulsed lasers. The process requires high power-densities and multiple irradiations at high scanning speeds to achieve the desired kerf depth. In this work a fast modulated cw fiber laser is used to investigate the possibilities of increasing the material removal rate by periodically dropping the laser power and therefore modifying the recoil pressure at the vapor-liquid interface in the interaction zone to assist in melt expulsion. It was found that power modulation with frequencies in excess of 10 kHz can lead to an increased material removal rate when compared to continuous wave processing at comparable average and peak power levels, enabling higher kerf aspect ratios in a single irradiation.

New insights into nonlinear optical effects in fullerene solutions—a detailed analysis of self-diffraction of continuous wave laser radiation

Spatial self-phase modulation (SSPM), i.e. the formation, temporal evolution and subsequent distortion of self-diffraction ring patterns, generated by transmitting a continuous wave 532 nm laser beam through solutions containing C60 or C70 has been investigated. The nonlinear optical response regarding SSPM of such systems was studied, to our knowledge for the first time, in dependence of various solvents, different sample temperatures and viscosities. The SSPM patterns consisted of a number of concentric rings, generated due to induced refractive index changes and start with a central spot, expanding into a series of concentric rings. The number of rings increases steadily and the ring pattern becomes larger with time until a maximum is reached. Thereafter, thermal convection leads to a distortion of the upper part of the ring system, while the lower part keeps its shape. The dependence of temporal and spatial evolution of self-diffraction ring pattern on different sample parameters and not only the functional material itself, leading to our conclusion that thermal effects are responsible for the observed SSPM. For further substantiation, measurements of C60 in toluene at a wavelength of 1070 nm have been carried out. At this wavelength no absorption occurs and no SSPM patterns were observed. Knowing that for ultashort pulses no significant thermal effects take place, we performed additional measurements at a pulse length of 8 ps and a wavelength of 527 nm. Also in this case no SSPM patterns were generated. In order to gain a deeper understanding of the involved physical processes, we developed a thermal blooming simulation: Thermally-induced refractive index changes and convection caused by locally heating of the solution by the laser beam were taken into account, any other nonlinear phenomena were left aside. A laser beam propagating through an absorbing solution generates similar ring structures under these conditions, what is in fully agreement with our experimental results. Additionally, as a practical application of SSPM a laser protection device is presented.

The influence of confined acoustic phonon on the quantum Peltier effect in doped semiconductor superlattice in the presence of electromagnetic wave

Based on the kinetic equation method, the quantum Peltier effect has been theoretically studied under the influence of confined acoustic phonon in doped semiconductor superlattice in the presence of the electromagnetic wave (laser radiation). There were complicated dependences of the analytical expression of the Peltier coefficient (PC) on quantities such as doped concentration of the superlattice, amplitude of the laser radiation, the cyclotron frequency of electrons and temperature of the system. In detailed consideration, the quantum number m was changed in order to characterize the influence of confined acoustic phonon. When setting the m to zero, we obtained the results that corresponded to the case of unconfined phonon. The theoretical results have been numerically evaluated and discussed for the GaAs:Si/GaAS:Be doped semiconductor superlattice (DSS). We found the oscillation of the PC according to enhancement of cyclotron frequency of electrons. Moreover, position of resonant peaks has shifted under the influence of phonon confinement. In the case of low doped concentration (n D), the PC decreased in non-linear way; then it reached a negative constant in high n D value. The non-linear change of the PC also has been detected when investigating its dependence on the laser amplitude. All numerical results have shown that the magnitude of the PC decreased due to the increase of phonon confinement effect. In short, the confinement of acoustic phonon caused the change of the quantum Peltier effect in DSS of GaAs:Si/GaAS:Be in quantitatively as well as qualitatively.

Effect of continuous wave, quasi-continuous wave and pulsed laser radiation on functional characteristics of fish spermatozoa

For the first time, using sturgeon sperm as a model system, sensitive to optical radiation, the comparative studies of biological effect of continuous wave, quasi-continuous wave, nano- and picosecond laser radiation under conditions with equal average irradiance (3 mW/cm2) and wavelength (532 nm) have been carried out. Analyzing the parameters of spermatozoa motion it has been shown that, depending on the energy dose and mode of laser operation, the radiation may have both stimulatory and inhibitory effect on the velocity of motion and spermatozoa motility duration as well as on sustaining of functional characteristics of cold-stored sperm. The possibility of increasing the fertilization rate due to use of the sperm preliminary treated with laser radiation is demonstrated. For the first time, the possibility of enhancement of biological effect going from continuous wave to quasi-continuous wave laser radiation at equal irradiance and wavelength has experimentally been proven. It is shown that the difference in biological effect of continuous wave, quasi-continuous wave, nano- and picosecond laser radiation is due to amplitude (peak) values of intensity. Using fluorescence analysis and luminol-dependent chemiluminescence assay, evidence for the participation of endogenous flavins and metal-free porphyrins in sensitized ROS formation (singlet oxygen, hydrogen peroxide, and hydroxyl radicals) in sturgeon sperm was obtained. Mechanisms of photochemical and photothermal reactions explaining the difference in efficacy of action of laser radiation in above modes are discussed.

Laser-based surface pre-treatment for metal-plastic hybrids using a new process strategy

Abstract In order to join metal-plastic hybrid parts so as to achieve lightweight constructions, innovative joining technologies are essential. For this, thermal joining is a promising approach due to the absence of any joining agent. The joint strength can be increased by surface pre-treatment of the metal with continuous wave laser radiation. Large joining areas, however, are challenging in terms of productivity, efficiency and geometrical flexibility when using conventional beam trajectories. A more promising approach is the use of continuous beam trajectories, which can be easily combined with on-the-fly processing. More precisely, a circularly oscillating laser focal spot is geometrically independent of every possible in-plane load direction, and causes lower thermal distortion of the metal sheet than using conventional beam trajectories. Therefore, the circular beam oscillation was characterized for the processing of large areas. In this context, the resulting topography of the metal was analyzed with respect to the surface roughness and a design criterion was mathematically derived and experimentally validated. Additionally, the joint strength was compared to the strength resulting from conventional beam trajectories. For verification, steel substrates were joined with a carbon-fiber-reinforced thermoset. The laser-based pre-treatment using the circularly oscillating laser focal spot led to a similar joint strength, while being more productive when combined with on-the-fly processing, compared to conventional structuring trajectories. Consequently, the processing time can be significantly reduced.

Reversibly pH-responsive gold nanoparticles and their applications for photothermal cancer therapy

Microenvironment responsive nanomaterials are attractive for therapeutic applications with regional specificity. Here we report pH responsive gold nanoparticles which are designed to aggregate in acidic condition similar to cancer environment and returned to its original disassembled states in a physiological pH. The pH responsive behavior of the particles is derived by change of electrostatic interaction among the particles where attraction and repulsion play a major role in low and high pH of the environment, respectively. Since different electrostatic interaction behavior of the particles in varied pH is induced not by irreversible chemical change but by simple protonation differences, the pH responsive process of assembly and disassembly is totally reversible. The low pH specific aggregation of gold nanoparticles resulted in red shift of plasmonic absorption peak and showed higher photothermal efficacy in acidic pH than in normal physiological pH. The low pH specific photothermal effect with long wave laser irradiation was directly applied to cancer specific photothermal therapy and resulted higher therapeutic effect for melanoma cancer cells than non-pH responsive gold nanoparticles.

Laser intensity limits in surface‐enhanced linear and nonlinear Raman micro‐spectroscopy of organic molecule/Au‐nanoparticle conjugates

AbstractLaser light, illuminating surface‐enhanced Raman scattering‐active nanostructured CeO2/Al/Al2O3 thin‐film samples with reporter molecules/Au nanoparticle conjugates on the CeO2 surface, may cause irreversible modifications of the conjugates and of the surface structure field‐enhancing properties. As a result, the observed Raman signal decreases or vanishes. The limits of the laser light intensity suitable for nondestructive spectroscopic studies have been assessed using continuous and quasi‐continuous wave (mode‐locked ps‐pulse) laser radiation at different wavelengths. This radiation was used as a pump for linear and nonlinear Raman microspectroscopy of reporter molecules adsorbed on the surface of such a plasmonic metamaterial. Reducing laser power below certain levels allowed reproducible mapping of surface‐enhanced Raman scattering and surface‐enhanced coherent anti‐Stokes Raman scattering signal strengths at the reporter molecule Raman shifts.

Photoprintable nanowire–polymer blends synthesized by dynamic emulsion polycondensation

ABSTRACTIn this article, we report a photoprintable nanocomposite synthesized at room temperature in less than 10 s by aggressive mixing of two monomer solutions. Polycondensation occurs in the dispersed phase of the dynamic emulsion, microdroplets, in which the nanofillers are suspended. Hence, the synthesized composite microparticles have a high dispersion and high loading of nanofillers. Specifically, silver nanowire (AgNW)–nylon 66 blends with various Ag weight fractions are synthesized and studied. The poly(vinyl pyrrolidone) (PVP)‐functionalized AgNWs (by polyol synthesis) are singly dispersed and tethered to the nylon matrix by PVP with a slight depression of the glass‐transition temperature. The Ag–nylon powder melts under low‐intensity visible continuous wave laser radiation; this allows convenient photoprinting of the nanocomposite structures. Photoprinting is demonstrated at a radiation intensity of 0.3 kW/cm2 (405 nm laser) and a scan rate of 5 mm/s for a 1.49 wt % Ag content. This enhanced photothermal characteristic of the nanocomposite, which allows printing at low radiation intensities, is attributed to the efficient coupling of light to the AgNW plasmon modes and the high dispersion of nanowires in the polymer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47670.

Recent Progress in Two-Dimensional Nanomaterials for Laser Protection

The Nobel Prize in Physics 2018, “For groundbreaking inventions in the field of laser physics”, went to Arthur Ashkin and Gérard Mourou and Donna Strickland. Their inventions have revolutionized laser physics and greatly promoted the development of laser instruments, which have penetrated into many aspects of people’s daily lives. However, for the purpose of protecting human eyes or optical instruments from being damaged by both pulsed and continuous wave laser radiation, the research on laser protective materials is of particular significance. Due to the intriguing and outstanding physical, chemical, and structural properties, two-dimensional (2D) nanomaterials have been extensively studied as optical limiting (OL) materials owing to their broadband nonlinear optical (NLO) response and fast carrier relaxation dynamics that are important for reducing the laser intensity. This review systematically describes the OL mechanisms and the recent progress in 2D nanomaterials for laser protection.

Nonlinear optical response of bulk ZnO crystals with different content of intrinsic defects

The nonlinear optical (NLO) properties of native defect-rich ZnO single crystals were studied in details within the excitation of the continuous wave (CW) and pulsed laser radiation at 532 nm (2.33 eV). Analysis of the experimental data of optical elastic scattering, Fourier transform infrared (FTIR), near infrared–visible–ultraviolet (NIR–Vis–UV) spectra recorded in reflection and absorption modes, and data of photoluminescence (PL) spectroscopy confirmed the contribution of both intrinsic defects and their clusters, being determined before by neutron diffraction and XRD analysis. It was shown that the high sensitivity of the NLO diagnostics via self-action of a laser beam is due to the resonant excitation of the deep defects states at wavelength 532 nm. It was also demonstrated the correlation of the real and imaginary parts of the cubic NLO susceptibility with PL and FTIR spectroscopies data dealing with the defect bands manifestation, while the elastic optical scattering and Vis-NIR spectroscopy data – with the intrinsic defect content. High photoinduced polarizabilities of the excited states provide application of the refractive NLO response and the optical elastic scattering indicatrices analysis as an express nondestructive technique to reveal the deep defects content in the bulk ZnO.

Electron dynamics in the laser and quasi-static electric and magnetic fields

3/2 dimensional Hamiltonian equations, accounting for arbitrary polarized plane wave laser radiation and arbitrary electric and magnetic fields in the directions both along and across to the direction of the laser beam propagation, are derived for superluminal phase velocity of the laser radiation. An impact of superluminal laser radiation phase velocity on the transition to stochastic electron motion is studied.

Laser induced non-monotonic degradation in short-circuit current of triple-junction solar cells

In order to study the continuous wave (CW) laser radiation effects and mechanism of GaInP/GaAs/Ge triple-junction solar cells (TJSCs), 1-on-1 mode irradiation experiments were carried out. It was found that the post-irradiation short circuit current (ISC) of the TJSCs initially decreased and then increased with increasing of irradiation laser power intensity. To explain this phenomenon, a theoretical model had been established and then verified by post-damage tests and equivalent circuit simulations. Conclusion was drawn that laser induced alterations in the surface reflection and shunt resistance were the main causes for the observed non-monotonic decrease in the ISC of the TJSCs.

Laser welding of copper using a high power disc laser at green wavelength

The trend towards renewable energies and electromobility is increasing the demand for copper. Laser welding as a flexible and fully automatable process is being more frequently employed to join copper materials. The use of green laser radiation compared to infrared laser radiation has the advantage of a significantly higher absorption coefficient for copper materials. Therefore, high power laser sources emitting at a green wavelength promise a more stable and a more efficient process. In this paper, experimental investigations with a green continuous wave laser radiation at a maximum power of 1 kW are presented. Using design of experiments, the process limits are determined depending on the laser power and the welding velocity. Furthermore, the potential of heat conduction welding using this laser source is investigated.

Transparent NaGdF4:Nd3+ colloid prepared by femtosecond laser ablation as a liquid laser medium

By using femtosecond-pulsed laser to ablate the larger nanosized target in liquid, stable transparent NaGdF4:Nd3+ colloid has been successfully fabricated. The X-ray diffraction (XRD) spectra reveal that the colloidal nanoparticles remain the hexagonal phase crystal structure of NaGdF4 powder target. SEM and TEM images results indicate that the size of these colloidal nanoparticles decreases sharply. FT-IR results indicate that the number of O–H and C–H groups on the surface is decreased. The emission properties of the colloid have been investigated using 794nm pulsed wave laser radiation, and it is found that the colloid exhibits near-infrared luminescent emissions in the spectral range of 850–1400nm, and the decay time for 4F3/2→4I11/2 (1058nm) Nd3+ ion transitions is lengthened than that of powder target, these results are probably due to the reduced nonradiative relaxation assisted by high energy oscillators. The observed near-infrared emission of the stable transparent colloid makes it a good candidate for application in liquid laser.

Glass processing with pulsed CO2 laser radiation.

Recent results of processing fused silica using a high-power Q-switched CO2 laser source with a maximum output power of 200 W are presented. Compared to the processing with continuous wave laser radiation, the main advantage of pulsed laser radiation is the influence of the light-matter interaction with high laser peak power at small average laser power. An application for the approach presented in this paper is the flexible manufacturing and form correction of optics. This laser-based process is nearly independent of the surface geometry and can even be enhanced by laser polishing and expanded to other glass materials. Hence, the high-power Q-switched CO2 laser source is used to ablate glass material with an ablation rate up to 2.35 mm3/s and also for ablating glass material locally in a vertical dimension down to 3 nm.