Action Of Pulsed Laser Radiation Research Articles

Numerical Simulation of Photoacoustic Effect in One-Dimensional Carbon Nanostructures

The paper describes methods for theoretical and numerical simulation of the photoacoustic effect that occurs in one-dimensional carbon micro- and nanostructures under an action of pulsed laser radiation. The proposed numerical modeling technique is based on solving the equations of motion of continuous media in the Lagrange form for spatially inhomogeneous media. This model makes it possible to calculate fields of temperature, pressure, density, and velocity of the medium depending on the parameters of laser pulses and characteristics of micro- and nanostructures.

Numerical simulation of Thermomechanical Effects in Absorbing Liquids upon Excitation by Pulsed Laser Radiation

Using the method of numerically solving the equations of motion of continuous media in the Lagrange form, simulations of the processes of excitation of pulsed acoustic beams during heating of absorbing liquids under an action of pulsed laser radiation has been carried out. The calculation of three-dimensional fields of temperature, pressure, density and velocity under the action of laser pulses with Gaussian spatial profile has been performed.

Photoacoustic effect in micro- and nanostructures: numerical simulations of Lagrange equations

The work provides the description of theoretical and numerical modeling techniques of thermomechanical effects that take place in absorbing micro- and nanostructures of different materials under the action of pulsed laser radiation. A proposed technique of the numerical simulation is based on the solution of equations of motion of continuous media in the form of Lagrange for spatially inhomogeneous media. This model allows calculating fields of temperature, pressure, density, and velocity of the medium depending on the parameters of laser pulses and the characteristics of micro- and nanostructures.

Changes in the characteristics of semiconductor structures of microwave amplifiers under the action of pulsed laser radiation

The effect of pulsed laser radiation on the change in the parameters of semiconductor structures of field-effect transistors with a Schottky gate with an operating frequency range of 1.5-8 GHz and integrated amplifiers with an operating frequency range of 0.4-6 GHz is studied. Laser radiation with 25 ns pulse duration, incident on the transistor crystal, creates a pulsed photocurrent. It is shown that the amplitude of the pulsed photocurrent is three times higher than the operating transistor current. The current-voltage characteristics of the field-effect transistor were measured in the mode of pulsed laser radiation. The amplitude dependence of the pulsed photocurrent in semiconductor structures on the power of laser radiation for various wavelengths of 1.06 μm and 0.53 μm is studied. It is shown that as a result of the action of pulsed laser radiation on semiconductor structures, a short disappearance of the amplification of the high-frequency signal at the amplifier output occurs. Keywords: laser radiation, transistor, microwave amplifier, photocurrent, current-voltage characteristic.

Model of the impurities redistribution in the surface layer of an alloy under the action of pulsed laser radiation

Model of the impurities redistribution in the surface layer of an alloy under the action of pulsed laser radiation

Изменение характеристик полупроводниковых структур СВЧ-усилителей под воздействием импульсного лазерного излучения

The effect of pulsed laser radiation on the change in the parameters of semiconductor structures of field-effect transistors with a Schottky gate with an operating frequency range of 1.5–8 GHz and integrated amplifiers with an operating frequency range of 0.4–6 GHz is studied. Laser radiation with 25 ns pulse duration, incident on the transistor crystal, creates a pulsed photocurrent. It is shown that the amplitude of the pulsed photocurrent is three times higher than the operating transistor current. The current-voltage characteristics of the field-effect transistor were measured in the mode of pulsed laser radiation. The amplitude dependence of the pulsed photocurrent in semiconductor structures on the power of laser radiation for various wavelengths of 1.06 µm and 0.53 µm is studied. It is shown that as a result of the action of pulsed laser radiation on semiconductor structures, a short disappearance of the amplification of the high-frequency signal at the amplifier output occurs.

Measurement of the spatial characteristics of an erosive silicon laser plasma using small-sized high-resolution spectrometers

The spatial characteristics of the erosion laser plasma are investigated. The application of small-sized spectrometers of the visible and ultraviolet ranges for recording the spectrum of plasma radiation is considered. Erosive laser plasma is formed on the surface of a silicon target under the action of pulsed laser radiation with a wavelength of 1064 nm under normal atmospheric conditions. The laser plasma torch was scanned using a movable slit diaphragm oriented parallel to the target surface. The emission of erosion laser plasma was recorded using small-size spectrometers. Based on the obtained plasma emission spectra, the dependences of the intensity of the spectral lines of silicon on the geometric position of the slit diaphragm are revealed. A comparison is made of the intensities of the spectral lines of silicon on the polished and grinded sides of the target.

Features of Vanadium-Surface Damage Induced by Pulsed Laser Radiation

The features of the damage of the surface layer of vanadium under the action of pulsed laser radiation are studied. Laser irradiation is carried out in air using a GOS 1001 setup in the Q-switching mode with the following parameters: flux power density q = 1.2 × 108 W/cm2, pulse duration τ0 = 50 ns, and number of pulses N = 1–6. The typical surface damages induced by the laser pulses are found to include the melting of material, a microcrack network, a wavy relief, and drop-like particles. The central region characterized by the greatest degree of damage contains also individual drops of metal, which crystallized like a spiral. The heat-affected zone (HAZ) adjacent to the central one is damaged to a significantly weaker extent. Surface degradation increases as the number of pulses increases. Laser irradiation is revealed to change the X-ray diffraction (XRD) patterns: loss of texture, presence of vanadium-oxide signal, peak broadening, and lattice parameter increase (from 3.022(2) to 3.027(3) A). It is shown that preliminary irradiation with argon ions (dose of 1022 m–2, E = 20 keV) affects no surface damage of the central region, while in the adjacent heat-affected zone, there is a spallation of local surface regions.

Изменение морфологии, структуры и микротвердости образцов циркониевого сплава в результате воздействия лазерными импульсами

The results of experimental studies on the modification of the surface layer of zirconium alloy grade E 110 by the action of pulsed laser radiation are presented. It was established that, as a result of laser treatment, the morphology of the surface layer changes with the formation of nanoparticles up to 50 nm in size. The relief of the treated surface becomes structurally heterogeneous, containing phases of zirconium and monoclinic ZrO2 dioxide. It was revealed that, as a result of exposure to laser pulses, a significant increase in the microhardness of the surface of zirconium samples occurs to 27.1 ± 0.1 GPa.

Experimental X-ray investigations of changes at the “solid-solid interface” boundary after pulsed focused laser irradiation

Abstract Investigated in this work were plates of Zerodur connected to a solid monolith block with the aluminum nanolayer of the 100-nm thickness. The object of the study was this nanolayer that changed its optical transparency under action of pulsed laser radiation. Zerodur plate located on the back side after ablation was step-by-step thinned by grinding and polishing up to the boundary with aluminum nanolayer. After each thinning step, we performed the X-ray phase analysis by using the diffractometer Philips X’Pert PRO – MRD. Used in this study was Cu Kαl emission line with the wavelength λ = 0.15405980 nm). The anode potential was 45 kV, and current – 40 mA. It has been ascertained that the changes in phase composition are present within the region of 50⋯100 nm from the aluminum nanolayer boundary. It has been found the appearance of the weak but sharp peak at 28.4° that corresponds to the reflection (1 1 1) of cubic silicon nanoparticles. Their size is approximately 12 nm. It was revealed the weakly pronounced but clear peak at 44.78° that corresponds to the reflection (2 0 0) attributed to cubic aluminum.

Influence of Hydrodynamic Processes Generated by 1.94-μm Pulsed Laser Radiation on Daphnia magna Crustaceans

The hydrodynamic processes occurring in water under the action of pulsed laser radiation with a power of 20 W, wavelength of 1.94 μm, and a pulse duration of 100 ns were investigated. Such radiation leads the excitation of jet flows in water, as well as microbubbles and broadband acoustic vibrations. It was established that the main energy of these vibrations lies within the range of 10–15 kHz; they are excited according to the thermal cavitation mechanism and the regime corresponds to superintense nucleate boiling. It was shown that laser-induced hydrodynamic processes exert a pronounced biological effect on Daphnia magna crustaceans, leading to their increased fertility for acoustic doses of 35 and 350 J/m2. The experimental data and theoretical estimates show that stimulation of the reproductive function in crustaceans is due to the action of laser-induced low-intensity broadband acoustic vibrations and is not associated with temperature effects. The death of crustaceans and appearance of individuals with maldevelopments were observed for the maximum exposure (300 s). It is shown that the negative effects are related only to the effect of high-temperature microjets on Daphnias.

Laser Pulse Annealing of Glass Plates Partially Covered by Radiation

The action of pulsed laser radiation on a plate is studied as a quasi-static problem of thermoelasticity. An analytic relation expressing the thermal strength condition for a plate is derived, making it possible to determine non-destructive regimes of laser processing in the case where the diameter of the laser beam is smaller than the diameter of the worked plate. The obtained results were checked experimentally.

Formation of ordered one-dimensional microstructures of dislocations in near-surface layer of semiconductor, under laser radiation with microstructured distribution of intensity

The paper presents the results of investigation the process of formation of the ordered microstructures of dislocations in the near-surface layer a single-crystal plate of silicon under the action of pulsed laser radiation with microstructured distribution intensity. It has been found that generation of the ordered one-dimensional microstructures of dislocations takes place. The period of these ordered microstructures is d≈3÷4 μm. A combination of one-dimensional structures of dislocations produces ordered two-dimensional structure of dislocations.

Effect of the recoil pressure induced by evaporation on motion of powder particles in the light field during laser cladding

A model is proposed, which takes into account acceleration of powder particles by a force induced by recoil of material vapors from the irradiated region of the particle surface. Results of a numerical analysis of heat and mass transfer in the case of motion of individual stainless steel powder particles in a gas flow and in a light field of laser radiation under conditions of laser cladding are presented. Acceleration of particles is found to depend on their diameter, carrier gas velocity, powder material properties, laser radiation power, and degree of attenuation of the power density in the laser beam in the direction of its action on the substrate. The calculated results are compared with experimental data on light-propulsion acceleration of individual particles (of aluminum, aluminum oxide, and graphite) under the action of pulsed laser radiation.

Heterogeneous laser ablation and its effect on the formation of a near-surface plasma under the action of pulsed laser radiation

The influence of the state of the target surface on the processes of near-surface plasma formation is studied in a wide range of wavelengths and laser-radiation pulse widths. These experiments made it possible to reveal the local character of the initial ablation of the target surface, caused both by surface defects and by the defects that appeared at an early stage of the action of the pulsed laser radiation because of the volume heterogeneity of solids. It is shown that the localness of the breakdown affects the evolution of the near-surface plasma formation. The differences in the character of the formation of the near-surface plasma are revealed when short pulses with rapidly increasing laser-radiation intensity act and when laser pulses with a slowly increasing leading edge act. It is established that the localness of the breakdown affects the evolution of the Rayleigh–Taylor hydrodynamic instability of the contact surface between the target vapor and subsequently the plasma and the gas surrounding the target, compressed by the leading shock wave.

Nonequilibrium effects accompanying the action of pulsed laser radiation on metals

This paper discusses two regimes of the laser ablation of metals (Al, Cu)—the nanosecond regime and the femtosecond regime. Mathematical modelling of nanosecond exposure has made it possible to determine the region where the single-temperature approximation can be applied. The laser pulse width must be at least 10 ns in this case. The modelling results showed that the nonequilibrium state has a qualitative effect on the main processes. They show up most clearly in femtosecond-exposure regimes, for which rapid phase transformations are accompanied by the appearance of strongly superheated (5000–15 000 K) metastable states and shock waves in the solid state, as well as by increased energy loss from the irradiation zone by electron thermal conductivity.

Changes in the refractive indices of absorbing liquids under the action of pulsed laser radiation

Changes in the refractive indices of weakly absorbing liquids exposed to pulsed laser radiation have been calculated as functions of space and time based on numerical solution of equations for continuous media motion in the Lagrange form, the heat-conduction equation, and the Lorentz–Lorenz formula.

Dispersion of zirconium dioxide by pulsed laser radiation

A technique for producing ZrO2 dioxide nanoparticles under the action of pulsed laser radiation is developed. By the methods of transmission electron microscopy and X-ray phase analysis, it is shown that the high-temperature cubic phase of ZrO2 is formed during laser ablation. The dependence of the size of ZrO2 dispersed particles on the laser radiation intensity is determined. A thermodynamic one-dimensional model of laser ablation of zirconium dioxide is analyzed. The results of analytical computations of ablation of ZrO2 particles are confirmed by experimental data.

Laser-induced surface vortex current in a thick film resistor

We have discovered a photoelectric skin effect and detected decaying high-frequency current excited in a silver-palladium thick film resistor under the action of pulsed laser radiation.

Temperature field formed inside a blood vessel under the action of pulsed laser radiation

A model that simulates the dynamics of the temperature field formed by pulsed laser radiation inside a biological structure containing blood vessels is developed. The threshold conditions of denaturation of vessel walls and subsequent blocking the blood flow are determined based on the thermochemical concept. The possibility of application of a pulsed modulation of the radiation for increasing the homogeneity of coagulation of vessel walls and reducing the risk of damage of tissues caused by the phase transition is considered. The modulation frequency range of radiation that ensures the realization of this effect is determined.