Power Density Of Laser Radiation Research Articles

Laser hardening of aerospace structural materials

The work is devoted to the study of laser shock treatment of structural materials used in aviation and space technology with powerful nanosecond pulses in order to reduce surface damage, as well as resistance to crack growth. The hardening effect is achieved due to the mechanical deformation produced by the shock wave from the laser pulse due to the rapidly expanding plasma in the area of the irradiation spot. In this work, laser parameters for processing structural materials are calculated to ensure the required laser radiation power density. The results of laser processing with high-power nanosecond pulses of materials such as oxygen-free copper, aluminum alloy and germanium at various energy densities, with and without a protective coating and a water layer are shown.

Effect of laser power density on formation of oxide particles during ablation of metallic bismuth in atmospheric air

Purposeful synthesis of bismuth oxide nanoparticles (NPs) of various crystal modifications is important for biomedicine, photocatalysis and other applications. In this work, pulsed laser ablation of a metallic Bi target in atmospheric air is used to obtain β-Bi2O3 NPs. The effect of the Nd:YAG laser radiation power density (1064 nm, 7 ns) in the range of 0.1–1.2 GW/cm2 on the features of formation of NPs under nonequilibrium conditions is studied, for which the spectra of laser-induced plasma are recorded and analyzed, the plasma composition is determined, and the temperature of the plasma plume is estimated. The NPs are comprehensively characterized using TEM, XRD, FTIR, Raman, and UV–Vis spectroscopies, and electrophoretic light scattering, which make it possible to determine their morphology, crystal structure, chemical composition, and optical properties. The photocatalytic activity of the resulting nanopowders in the Rhodamine B dye decomposition reaction is assessed.

Photovoltaic AlGaAs/GaAs devices for conversion of high-power density laser (800–860 nm) radiation

Photovoltaic converters of high-power (λ = 800–860 nm, ELR = 150–550 W/cm2) laser radiation (PhotoVoltaic Laser Power Converters – PVLPCs) based on AlGaAs/GaAs heterostructures grown by metalorganic vapor-phase epitaxy have been developed. To increase the output voltage, the space charge region of p-GaAs/n-AlхGa1-хAs heterojunction was shifted to the n-AlхGa1-хAs wide-gap layer with a gradual “x”. The technology for embedding a rear reflector based on TiOx/SiO2/Ag into the photovoltaic converter structure by “transferring” the heterostructure to a supporting substrate and the method of bonding to form a monolithic structure of the PVLPC has been elaborated. To operate the heterostructures at an increased power density of laser radiation, they have been designed to eliminate possible potential barriers at the heterointerfaces and the frontal contact topology with a high density of the metal grid (50 μm and 125 μm contact pitch are under consideration) has been employed. PVLPCs with efficiency of 62% were obtained at the power density of monochromatic radiation (λ = 850 nm) ELR = 170 W/cm2. The finger pitch of 50 μm allows keeping efficiency more than 56% even with a fivefold increase in laser radiation (up to ELR = 500 W/cm2).

The Laser Influence on the Formation of Ni-Al Compounds in the Nickel Foil Surface Layers Depending on the Laser Radiation Power Density

The Laser Influence on the Formation of Ni-Al Compounds in the Nickel Foil Surface Layers Depending on the Laser Radiation Power Density

Optimization of 12Х18Н9Т-Steel Processing by Ring Laser Beams

Using the MOGA genetic algorithm built into the DesignXplorer module of the ANSYS Workbench program, optimization of laser processing of 12Х18Н9Т-steel by annular beams has been performed. The calculation of temperature fields has been carried out taking into account the dependence of the thermophysical properties of the material on temperature by the finite element method in the ANSYS Workbench program. A regression model has been obtained for processing 12Х18Н9Т-steel by annular laser beams using a face-centered variant of the central compositional plan of the experiment. The power density and duration of laser radiation pulses, the outer and inner diameters of the laser beam in the processing plane were used as variable factors. The penetration depths of the material and the maximum temperatures in the laser processing zone were used as responses. The influence of processing parameters on the penetration depths of the material in the laser impact zone and the maximum temperature values has been evaluated. It has been established that the depth of penetration of the material and the maximum temperatures are most affected by the power density of laser radiation. Optimization of laser processing of 12Х18Н9Т-steel by annular beams was carried out by setting the limiting values of the maximum tempe-rature in the processing zone for three variants of the minimum penetration depth. The parameters obtained as a result of optimization using the MOGA algorithm and the parameters obtained as a result of finite element modeling are compared. The maximum relative error of the results when determining the maximum temperatures did not exceed 1 % and when determining the maximum penetration depths did not exceed 6 %.

Effect of New Design of the Laser Installation and Spraying Method on the Physical and Mechanical Properties the Inner Surface a Small Diameter Coated with 15Cr17Ni12V3F35ZrO2

A unique controlled laser head with an adaptive module was developed to stabilize the trajectory of movement. The scientific and practical problem of developing a technology for restoring the inner surface of a small diameter up to ∅44 mm was solved by the introduction of a laser head. Adhesion was achieved by moving the laser along the vectors, forming a regular pyramid with opening angles at the top. High physical and mechanical properties of the restored pump surface were achieved by the laser technology when spraying powder composition 15Cr17Ni12V3F35ZrO2. The optimal values of the microhardness of the coating of 5000 MPa were achieved due to the optimal transition melting zone of 0.8 ÷ 1.45 mm; the laser radiation power density of 3 × 105 W/cm2; and the diameter of the focus spot of the laser beam of up to 1.3 mm. High corrosion resistance and tribology were achieved by an optimally matched distance of 10 ÷ 15 mm and a surfacing speed of 15 mm/s. Homogeneous spheroidized particles of the material were observed in the martensitic phase of the structure. The stable compression stresses in the phase structure during the laser deposition of zirconium dioxide were fixed at the level of 1.0 ÷ 1.5 N/m2, and the compression stresses were at the level of 0.2 ÷ 0.4 N/m2. A multifactorial experiment established the dependence of the coating hardness on the distance to the focal plane and the energy characteristics of the laser source, providing optimal laser parameters (area, pulse power, and duration).

Pyrolysis of High Volatile C Bituminous Coal under the Action of Nanosecond Laser Radiation

The effect of pulsed nanosecond laser radiation (wavelength 532 nm, pulse duration 14 ns, pulse repetition frequency 6 Hz, the density of laser radiation power 0.2–0.6 J/cm2) on the tableted samples of high volatile C bituminous coal in argon medium is investigated. Among the gaseous products of pyrolysis, H2, CH4, C2H2, CO and CO2 are detected. The volume fractions of gaseous products from sample pyrolysis depending on the laser radiation power density is established. Within the laser radiation power density range 0.2–0.4 J/cm2, the volume of the formed combustible gases per unit mass of the reacted sample increases, and remains almost unchanged with further increase in power density. The volume fraction of combustible gases in the mixture of gaseous pyrolysis products are only slightly dependent on the laser radiation power density. The action of nanosecond laser radiation with a power density of more than 0.4 J/cm2 causes intense ablation of the tableted sample containing 0.005 wt.%. polyvinyl alcohol. A tableted sample containing no binding material is destroyed under the action of nanosecond laser radiation with a power density of more than 0.2 J/cm2.

Synthesis and optical characteristics of silver nanoparticles produced by laser ablation of metal in liquid

The process of silver ablation in water by high-power laser pulses (λ = 1064 nm, τ = 20 ns) in the power density range from 2.6 ⋅ 108 to 5.5 ⋅ 108 W/cm2 has been investigated. The dependences of the ablation efficiency and the size distribution of silver nanoparticles on the power density of laser radiation and on the duration of synthesis have been determined. It was found that the resulting nanoparticles have a multimodal size distribution, in which three fractions with average sizes of 5; 50 and more than 100 nm can be distinguished. Particles with a diameter of more than 100 nm are formed as a result of the removal of the liquid-droplet phase directly from the target surface due to the hydrodynamic mechanism, particles 5 and 50 nm in size are formed due to condensation at different stages of cooling of the vapor-plasma formation. The proportion of these fractions in the silver sol is determined by the effective density of the laser power on the target surface. It is shown that pulsed laser irradiation of a sol of silver nanoparticles after the completion of the synthesis process makes it possible to significantly narrow the particle size distribution and increase the stability of the resulting suspension. It was found that the synthesised silver nanoparticles deposited on a silicon substrate can effectively enhance the Raman signal of human serum albumin.

Laser Treatment as a New Approach to the Passivation of Iron-Based Historical Monuments

This article is devoted to the study of the possibility of the passivation of iron-based metallic materials. The experimental results obtained for the laser treatment of carbon steel model samples by the radiation of repetitively pulsed and continuous-wave 1.064 µm Nd:YAG lasers are described. It is shown that the laser treatment allows the formation of dense protection films, 62–77 microns thick, on the steel surface. The films enhance the anticorrosion properties of the metal. Exposure to laser radiation reduces the surface roughness (from Ra = 0.53 µm to Ra = 0.38 µm). Laser radiation power densities of 10.2 × 105 W/cm2 and 10.7 × 105 W/cm2 for these two laser generating modes, respectively, correspond to the optimum (in terms of the degree of corrosion resistance) modes of steel treatment. The conducted studies show that the application of Nd: YAG lasers is a promising method for the surface passivation of artworks created from steel and cast iron. One of the most promising applications of the proposed method for the anticorrosion protection of iron is the passivation of the surface of iron-based historical monuments.

A GaInP-based photo-converter of laser radiation with an efficiency of 46.7% at a wavelength of 600 nm

GaInP-based laser power converters (LPC) structure grown by MOVPE and device chip design have been optimized for operation under high-power lasers of the green-red spectral range. Light I-V curves records have shown the performance of the LPC at up to 40-50 W/cm2 of incident power densities. The highest level data were obtained for 532, 600, and 633 nm power laser lines: 44.3%, 46.7%, and 40.6% under 13-16 W/cm2, respectively. LPC demonstrated an efficiency of more than 40% at the incident laser radiation power density elevated up to 40-50 W/cm2. Keywords: laser photoconverter, MOVPE, efficiency, spectral response.

Nucleation under the impact of pulsed laser radiation

The article shows theoretical calculations of nucleation in nonequilibrium conditions under the impact of high-power laser radiation, and their experimental confirmation. The phase transition during homogeneous nucleation without seed in the gas phase has long been studied by various scientists in the developed countries of the world. Several nucleation theories have been developed, however, they are difficult or impossible to apply to fast-flowing crystallization processes occurring at high pressures and temperatures that take place when using high-power laser radiation in the gas phase. In this article, an extended model of nucleation in the gas phase is developed using traditional thermodynamic concepts, as well as the influence of the process conditions on the equilibrium concentration and the formed particle size within the range from 100 nm to 1 micron is predicted. The article describes experiments on growing structures on plastic substrates containing inside optical inhomogeneities in the form of diffraction gratings. The calculation of the sublimation evaporation pressures of aluminum is conducted depending on different laser radiation power densities. The authors obtained images of nascent structures by electron microscopy and demonstrated the possibility of observing the nucleation phases in situ by changing the power of laser radiation of the sample.

Investigation of laser and thermal sintering processes of silver nanoparticles agglomerates synthesized by spark discharge

Changes in the shape and size of silver nanoparticles (NPs) during their laser and thermal sintering have been studied experimentally and theoretically. Aerosol silver NPs forming dendrid-like agglomerates 180 nm in size were synthesized by spark discharge and exposed to laser radiation and high temperature of 750 °C. The shape and size of the NPs were investigated depending on the power of the laser radiation and the temperature of the gas. It is estimated that, at a power density of laser radiation of the order of 103-104 W/cm2, the formation of spherical NPs with an average size of 140 nm is expected. Such particles turn out to be similar to NPs thermally heated in a gas flow at 750 °C for 6 seconds.

Photodynamic therapy of the experimental tumors of different morphological types with liposomal boronated chlorin е6

The article summarizes the results of studies of the effectiveness of photodynamic therapy using a new domestic photosensitizer liposomal borated chlorin e6 (LBC) after its parenteral administration (intraperitoneal and intravenous). Antitumor efficacy was evaluated in rats with M-1 sarcoma and PC-1 alveolar liver cancer and mice with B16 melanoma and Ehrlich’s carcinoma, which were transplanted subcutaneously into the thigh area of the animals. The aim of the study was to determine the optimal regimes of photodynamic therapy that would allow achieving the maximum antitumor effect up to 21 days after the photodynamic therapy. The therapy was carried out under the control of the accumulation of the photosensitizer in the tumor and surrounding tissues of the thigh by selecting the doses of the drug and the parameters of laser radiation (energy density and power density). The effectiveness of therapy was assessed by the inhibition of tumor growth, by the percentage of animals with complete tumor regression, by the absolute growth rate in animals with continued tumor growth compared to controls. The results of our studies have shown that the domestic photosensitizer liposomal borated chlorin e6 has high antitumor activity in vivo. In an experimental study of the photosensitizer under certain PDT modes, the maximum antitumor effect (complete tumor regression in 100% of animals) was obtained up to 21 days after PDT in all tumor models used.

Photodynamic therapy as a treatment option for skin cancer, developed on scars

It is given a literature reference on the etiology, frequency and mechanisms of development, features of the clinical presentation and treatment options for skin cancer that has developed on scars. It is presented a detailed clinical observation of a patient with squamous cell skin cancer in the area of the right elbow joint, which occurred 67 years after the kerosene lamp burns of the skin of the right upper limb and the right half of the chest. The patient was initially treated with electron radiotherapy in the total focal dose 60 Gy with a partial effect, but after 10 months a relapse was diagnosed, for which multi-course photodynamic therapy was performed with a Photolon photosensitizer at a dose of 1.1 mg/kg; the way of light delivery was polypositional interstitial and distant, the laser radiation power density was 0.30 W/cm2, the laser radiation energy density was 200 J/cm2. The result of treatment is complete regression of the tumor, the patient was under regular observation without any signs of local, regional and distant metastasis. After 3 years, by the absence of signs of local relapse, the disease progression was diagnosed: metastatic lesion of the axillary lymph nodes on the right and multiple metastases in the lung tissue of both lungs. Treatment was performed: axillary lymphadenectomy on the right, targeted therapy with IgGl monoclonal antibodies directed against the epidermal growth factor receptor; on this background stabilization of the process was noted.

Pulsed laser deposition of Au nanoparticles on ZnO nanostructures

Au nanoparticles and ultrathin gold films were obtained on the surface of thin (100 nm) ZnO films on Si (001) by pulsed laser deposition (PLD) at high argon pressure by sputtering a pure gold target with a CL3100 pulsed excimer laser (λ = 248 nm) at room temperature. The dependence of the size and distribution of nanoparticles on the argon pressure in the vacuum chamber (PAr), the power density of laser radiation (j), and the number of laser pulses (N) was investigated. Also, to obtain nanostructures, axial and non-axial deposition was used, where the substrate was located perpendicular and parallel to the plasma torch, respectively. Stable modes of obtaining gold nanoparticles with high uniformity and average size from 4 to 10 nm were demonstrated. The modes of stable and reproducible deposition of ultrathin Au films (23-42 nm) and percolation structures (18-20 nm) were also demonstrated. Thus, PLD is a reliable and flexible tool for obtaining nanoparticles and ultrathin Au films the average size and thickness of which can be predictably controlled by varying the deposition parameters. This technique is well suited for coating with gold nanoparticles the surface of nanostructured materials based on chemically active substances that are particularly sensitive to surface cleanliness, which cannot be coated by standard methods.

Nature of Degradation in Semiconductor Lasers with Electronic Energy Pumping. Theoretical Background

. Catastrophic degradation takes place in case of reaching critical values of laser radiation density power in semiconductor lasers with electronically pumped energy made from single crystals of some compounds. It has been accompanied by mechanical destruction of the surface at resonator ends, an irreversible decrease in radiation power and an increase in generation threshold. Moreover, during the catastrophic degradation of semiconductor lasers under the action of intrinsic radiation, significant changes in the crystal structure occur within the single crystal: dislocation density reaches a value more 1012–1015 cm–2. It has been shown that initial density of dislocations and critical power density of the intrinsic radiation are inversely proportional. Thus, the degradation process of semiconductor lasers is directly related to generation and multiplication of dislocations during laser operation. Mechanical destruction of a crystal lattice occurs at critical values of laser radiation power and dislocation density. To clarify the proposed mechanism for the degradation of semiconductor lasers, it is necessary to take into account an effect of dislocations on optical properties of semiconductors. Typically, this effect is considered as follows: dislocations cause an appearance of a local deformation field and, in addition, form space-charge regions that surround a dislocation core in the form of a charged tube. The paper proposes a model of the phenomenon under study: large stresses arise in the dislocation core, leading to a displacement of individual atoms and deformation of the crystal lattice. Lattice deformation in the dislocation core leads to a local change in the width of a forbidden band. This change value is about 10–2 eV for a screw dislocation and 10–1 eV for a boundary dislocation. The mechanism of this change is that aforementioned deformation leads to a multiple rupture of electronic bonds and an increase in the electron concentration in the dislocation core to approximately value 1018 cm–3. The developed analytical model of the degradation mechanism allows to perform selection of a semiconductor and estimation of a laser operating mode under conditions of increased radiation power.

Structure and properties of zirconium oxide films doped with yttrium oxide obtained by laser deposition in vacuum

The thin films deposited in vacuum (2 ⋅ 10–2 mm Hg) on the silicon and glass substrates under the multi-pulse high-frequency (10 –15 kHz) laser exposure (laser radiation power density 100 MW/cm2 and the distance from the target to the substrate 40 mm) for zirconium oxide ZrO2 ceramics doped with yttrium oxide 5 % Y2O3. The morphology of the obtained films was studied using atomic force microscopy. The features of transmission spectra in the visible, near infrared and middle infrared region were revealed. The transmission of the zirconium oxide film on the silicon substrate reached 12 % in the spectral region from 1.0 to 2.5 μm, and in the region from 2.6 to 6.0 μm was 4.7 %. On a glass substrate, the transmittance at a wavelength of 643 nm was 60 %, and at a wavelength of 2500 nm it reached 87 %. In the middle infrared region, transmission at a frequency of 2548 cm–1 was 70 % and reached 75 % at a frequency of 3566 cm–1. The volt-ampere and capacitance-voltage characteristics of the obtained zirconium oxide films were characterized by non-linearity, including hysteresis, and are probably due to the presence of discrete surface states with a wide energy spectrum associated with nanoparticles and nanocrystalline film inclusions.

Near-Surface Plasma Formed by Dual-Pulse Laser Action at Two Wavelengths on Titanium in Air

Spectra and structures of near-surface plasma torches were studied experimentally by measuring the specific mass loss and plume luminosity caused by dual-pulse laser radiation at wavelengths 1064 and 532 nm on titanium in air as functions of the time between laser pulses and their sequence. Dependences of the laser-plasma temperature and concentration of charged particles on the paired laser pulse parameters were established at laser radiation power densities q1064 ≤ 3.1·109 and q532 ≤ 2.7·109 W/cm2 for λ = 1064 and 532 nm. The optimal conditions for recording erosion plasma spectra had the initial effect from second-harmonic radiation with a time interval between pulses of 4–5 μs; for specific mass loss, 3–6 μs. The results were important for enhancing the efficiency of laser emission spectral analysis and laser-plasma processing of materials.

Tailoring the collagen film structural properties via direct laser crosslinking of star-shaped polylactide for robust scaffold formation.

Application of restructured collagen-based biomaterials is generally restricted by their poor mechanical properties, which ideally must be close to those of a tissue being repaired. Here, we present an approach to the formation of a robust biomaterial using laser-induced curing of a photosensitive star-shaped polylactide. The created collagen-based structures demonstrated an increase in the Young's modulus by more than an order of magnitude with introduction of reinforcing patterns (from 0.15 ± 0.02 MPa for the untreated collagen to 51.2 ± 5.6 MPa for the reinforced collagen). It was shown that the geometrical configuration of the created reinforcing pattern affected the scaffold's mechanical properties only in the case of a relatively high laser radiation power density, when the effect of accumulated thermomechanical stresses in the photocured regions was significant. Photo-crosslinking of polylactide did not compromise the scaffold's cytotoxicity and provided fluorescent regions in the collagen matrix, that create a potential for noninvasive monitoring of such materials' biodegradation kinetics in vivo.

High-Efficiency Conversion of High-Power-Density Laser Radiation

AlGaAs/GaAs-based semiconductor photovoltaic converters (PVCs) of laser radiation, capable of operating at an illuminance up to 9 kW/cm2 with retained isothermal state have been studied. This state was confirmed by the logarithmic shape of dependences of the open-circuit voltage on the power density of incident laser radiation. At maximum illuminance, the open-circuit voltage level was close to 1.33 V. It is shown that the proposed PVCs can provide laser radiation conversion at an 840-nm wavelength with efficiency above 51% at an incident radiation power density of 2.5 kW/cm2.