Laser-supported Detonation Wave Research Articles

Observation of Oblique Laser-Supported Detonation Wave Propagating in Atmospheric Air

Elucidation of the propagation velocity of a laser-supported detonation (LSD) wave and its propagation mechanism is necessary for various engineering applications. This study was conducted to observe an oblique laser-supported detonation wave off the laser axis. The relation between the local laser intensity and detonation-wave propagation velocity was investigated. For this purpose, the time-space distribution of the laser intensity was measured precisely. The change of the LSD wavefront shape was visualized using an ultrahigh-speed camera. The relation between the local laser intensity and the propagation velocity of the oblique LSD wave measured off the laser axis was found to be identical to the relation between the local laser intensity and the detonation propagation velocity at the laser axis.

Laser energy partitioning in nanosecond pulsed laser-induced air breakdown: effect of incident laser energy.

Air breakdown is generated by a 1064nm nanosecond pulsed laser beam, and laser energy deposited in the breakdown (E d), transmitted through the plasma region (E t) and carried away by the shock wave (E s) is estimated for the incident laser energy (E i) range of 60-273mJ. The E d is approximately 85% of E i at 60mJ, rapidly increasing to 92% at 102mJ. The shock wave front velocity and radius are measured as a function of E i and propagation distance. The shock wave velocity nicely follows the v∝E i0.3 trend predicted by the laser-supported detonation wave model. The Sedov-Taylor theory is used to estimate E s, which rapidly increases with E i, but E i to E s conversion linearly decreases from 83% to 48%. At lower values of E i, most of the laser energy is carried away by the shock wave, whereas the laser energy used in plasma heating or released in the form of electromagnetic and thermal radiation becomes important at higher laser energies. This implies that laser energy partitioning is highly dependent on the value of incident laser energy. These findings provide important insights into the fundamental physics of air breakdown and will be useful in a variety of applications such as laser-induced breakdown spectroscopy, laser ignition, and laser propulsion.

Plasma Emission, Wave Speeds, and Temperatures of Laser-Supported Plasmas in Air

A study of the generation and subsequent expansion of plasmas using a single beam (532 nm) from the second harmonic generator of a Q-switched Nd:YAG laser is described. The plasmas in air are studied using an intensified charge-coupled device camera over periods of 1000 ns following the laser pulses. The plasma experimental results are interpreted in terms of wave speeds and plasma temperatures. Energy balance equations are considered to estimate the plasma temperatures and the laser-supported radiation (LSR) and the laser-supported detonation (LSD) wave speeds. Within 1000 ns observation time, the circular spectral images turn elliptical because of plasma expansion toward the laser beam. The plasma expansion increases with increasing laser irradiance. A laser irradiance range of yields LSR wave speeds between 45 and 170 km/s and LSD wave speeds of 90–130 km/s. The measured wave speeds are compared with the LSR and the LSR wave speed models. The plasma temperatures are between 90,000 and 120,000 K at 15 ns after the laser pulse based on measured emission spectra and are between 640,000 and 760,000 K at 3 ns based on the LSR model.

Hugoniot Relation for a Bow-Shaped Detonation Wave Generated in RP Laser Propulsion

Repetitive-pulsed (RP) laser propulsion is expected to replace chemical propulsion systems because it can reduce launch costs. A laser-supported detonation wave (LSD) plays an important role in the thrust-generation process of RP laser propulsion. The LSD propagation mechanism has been studied. Nevertheless, the LSD propagation velocity measured in an earlier study was lower than the Chapman–Jouguet (CJ) velocity, which meant that Hugoniot analysis produced no solution. The findings suggest that the radial flow from the central axis of LSD exerts some effects, but it has not been evaluated quantitatively. Two-dimensional axisymmetric computational fluid dynamics (CFD) analysis using the measured propagation velocity was performed for this study to evaluate effects of the radial flow of a bow-shaped LSD. Results show that the ratios of the radial flow of mass, momentum, and enthalpy from the central axis can be calculated, respectively, as 0.82, 0.13, and 0.17. Additionally, the measured propagation velocity of a bow-shaped LSD was shown to be higher than the CJ velocity calculated using the two-dimensional axisymmetric CFD reproducing the experiment conditions.

Study of the length and influencing factors of air plasma ignition time

Abstract When a high-energy laser acts on a film surface, plasma flashes of both the air and film can be generated simultaneously. However, when the conventional plasma flash method is used to identify thin film damage, there is a misjudgment problem caused by the inability to distinguish the air and film plasma flashes. In order to solve the problem of misjudgment, the ignition times of air and thin film plasma flashes can be obtained, respectively. If the ignition times of air and thin film plasma flashes are not equal, they can be distinguished from the time difference. In this paper, a nanosecond Nd:YAG pulse laser is used to break down the air at room temperature and pressure, and the theoretical and experimental values of the ignition time of air plasma flash are obtained. The curves of the ignition time of air plasma flash with the laser wavelength, incident energy, focusing spot, and pulse width are simulated. The reasons for the changes are analyzed from the perspectives of multiphoton absorption, cascade ionization theory, and electromagnetic theory of laser breakdown gas. The results show that when the laser pulse width is 10 ns, the energy is 160 mJ, and the spot radius is 0.015 cm. The theoretical and experimental values of the ignition time of air plasma flash are 2.146 and 2 ns, respectively, which are in good agreement. Larger values of laser focus spot size and pulse width relate to a longer ignition time of the air plasma flash, whereas larger values of laser wavelength and incident energy are related to a shorter ignition time. The research reflects the characteristics and electronic transition of air plasma, as well as the micromorphological evolution of the interaction between laser and air, presents the process of air plasma flash generation and growth, and reveals the ignition mechanism of air plasma. It not only provides a basis for improving the traditional plasma flash identification method to identify film damage but also has a certain scientific significance for studying the generation mechanism of laser-supported combustion waves and detonation waves.

Numerical Simulation of Damage Effect for Ferroelectric RAM Irradiated by Space High-Energy Particles

In order to simulate the damage effect of space high-energy particle interacting on ferroelectric random access memory (RAM), the theoretical model of laser supported detonation wave is derived. Also, the equivalent target model of the collision between the core region of the ferroelectric RAM and high-energy particles is established. The high-energy oxygen and nitrogen atoms are selected as the sources of high-energy particles in the air at normal temperature and pressure. The source of particles that bombard the ferroelectric RAM is used to simplify the simulation of the composite target. Meanwhile, the theory of molecular reaction dynamics, the particle collision software based on the Monte Carlo algorithm provided by Stopping and Range of Ions in Matter (SRIM), is used to simulate the collision of high-energy particles with air. The simulated results show that the electron stopping capability of air to high-energy nitrogen and oxygen atoms is far greater than the stopping capability of the nucleus; when the incident energy of high-energy particles is gradually increased, the blocking power of air to electrons increases first and then decreases. Also, the capability to stop the particles of the target nucleus is gradually reduced; under the condition of the implantation, the energy of nitrogen and oxygen atoms are both 1.8 MeV, the movement of the particles in the first seven layers of the target is relatively straight, and the phenomenon of deviation from the axis of symmetry is apparent in the silicon substrate. Due to the presence of more energy in the first seven layers of the target, it is not possible to see the more obvious lateral diffusion. The simulated results will provide a valuable reference for the prediction of single-event effects induced by ground-based pulsed laser simulating space high-energy particle irradiation.

Species distribution in laser-induced plasma on the surface of binary miscible alloy

The spatiotemporal species distribution and dynamics of plasma play a crucially important role in improving the quality of the deposited film fabricated by pulsed laser deposition (PLD) and optimizing the spectral acquisition to enhance the quantitative performance of spatial-resolved laser-induced breakdown spectroscopy (LIBS). In this work, the monochrome imaging is used to analyze the plasmas induced from binary miscible alloys and explore the dependence of species distribution in plasma on laser-supported combustion (LSC) and laser-supported detonation (LSD) wave propagation regimes. This paper includes three conclusions: 1) the species distribution in LSC-wave dominated plasma induced from immiscible alloy is heavily influenced by the melting points of constituted elements, while in LSC-wave dominated plasma induced from miscible alloy, it is related to the boiling points; 2) whether the alloy is miscible or immiscible, the species distribution in LSD-wave dominated plasma is only related to the atomic masses; 3) to a great extent, the reduction rate of species in LSC-wave dominated plasma is associated with the transition probability, while that in LSD-wave dominated plasma is associated with the number density of species in the upper energy level.

Evaluation of electron temperature and electron density of laser-ablated Zr plasma by Langmuir probe characterization and its correlation with surface modifications

AbstractThe plasma parameters of laser-ablated Zirconium (Zr) using a Langmuir probe technique have been investigated by employing a Q-switched Nd:YAG laser (532 nm, 6 ns) at various irradiances ranging from 8.6 to 15.5 GW/cm2. All the measurements have been performed under an ultra-high vacuum condition while keeping the probe at a fixed distance of 4 mm from the target. By varying the biasing voltages from 1 to 75 V, the corresponding values of electric currents are measured by the probe on the oscilloscope. Laser-induced Zr plasma parameters such as electron temperature, electron number density, plasma potential, Debye length, and thermal velocity have been evaluated from I–V characteristic curves of Langmuir probe data. It is found that both the electron temperature and thermal velocity of Zr plasma reveal an increasing trend from 18 to 41 eV and 2.8 × 108 to 4.3 × 108 cm/s, respectively, with increasing laser irradiance which is attributed to more energy deposition and enhanced ablation rate. However, the electron number density of Zr plasma exhibits a non-significant increase from 6.5 × 1014 to 6.7 × 1014 cm−3 with increasing irradiance from 8.6 to 10.9 GW/cm2. A further increase in irradiance from 12 to 15.5 GW/cm2 causes a reduction in the number density of Zr plasma from 6.1 × 1014 to 5.6 × 1014 cm−3 which is attributed to the formation of thick sheath, ambipolar electric field, and laser-supported detonation waves (Shock front). Scanning electron microscope analysis has been performed to reveal the surface morphology of irradiated Zr. It reveals the formation of cracks, ridges, cones, and grains. It was observed at high irradiances the ridges are vanished, whereas cones and cracks are dominant features. By controlling plasma parameters, surface structuring of materials can be controlled, which has a vast range of applications in the industry and medicine.

Characterization of the fast ionization wave induced by a CO2 laser pulse in argon

Fast ionization wave (FIW), a postbreakdown phenomenon of laser-induced plasma, is observed for a laser intensity of 1011–1013 W/m2 using the CO2 laser pulse in the atmospheric pressure condition. FIW is distinguishable as “overdriven detonation” according to Raizer's Chapmann-Jouguet detonation theory because FIW is known as the type of laser-absorption wave that has a higher propagation velocity than the laser-supported detonation wave (LSDW). Some reports have described the expansion of FIW using a solid-state laser. Nevertheless, the threshold phenomena between FIW and LSDW are not fundamentally understood. This study used the high-speed visualization and optical emission spectroscopy to investigate the transition of the laser-absorption wave in argon gaseous form. To elucidate the physics of the transition threshold, a 5 J CO2 pulse laser, an Echelle spectrometer, and an intensified CCD camera are used for the quantitative investigation of the plasma temperature and density. Results demonstrate that the FIW front had an electron temperature of 0.7 eV and an electron number density of 2.5 × 1023 m−3. At the FIW–LSDW transition, the electron temperature increased by 1 eV, and the density decreased by 2.2 × 1023 m−3. Besides, the transition threshold and the existence of local-thermodynamic equilibrium were evaluated based on the electron temperature, and the density was obtained from the spectroscopic experiments.

Signal enhancement of laser-induced breakdown spectroscopy on non-flat samples by single beam splitting.

A single-beam-splitting approach was employed to enhance the signal intensity of LIBS under the extreme condition of laser beam grazing the surface of non-flat samples. Examining the time-integrated emission spectra shows that ISplit/ISingle enhancement factors of 2.5 and 3.5 were achieved at the laser energy of 33 mJ for aluminium alloy and brass, respectively. This factor first increases, reaches its maximum at 33 mJ, and drops gradually with the laser energy further increased. The mechanisms behind the enhanced optical emission and the enhancement factor evolution are discussed by using the proposed laser ablation model and laser-supported detonation (LSD) wave model, respectively. Examining the time-resolved emission spectra show that enhancement effect exists across all the plasma expansion process and the split beam mode allows for a longer plasma lifetime. A remarkable feature is that the trailing phenomenon emerging in the single beam mode vanishes due to the interaction between the plasmas generated by the grazing incident and normally incident laser beams in the split beam mode. The underlying cause is probably that the plasma plume produced by the normally incident laser beam prevents the grazing incident laser beam from further propagating and ablating the sample surface below. These findings not only give an insight into the plasma generation and evolution at grazing incidence of laser beam on sample surface but also provide a more reliable method for outdoor LIBS measurement of irregular samples.

Species distribution in laser-induced plasma on the surface of binary immiscible alloy

Investigation on species distribution of vapor plasma is of great significance for understanding the laser-target interaction, the plasma dynamics and verifying theoretical models. It is also helpful for optimizing the spectral acquisition to improve the quantitative performance of spatial-resolved laser-induced breakdown spectroscopy (LIBS). In this work, the laser-induced plasma on the surface of binary alloy is analyzed by using spectrally, spatially and temporally resolved dual-wavelength differential imaging to explore the dependence of species distribution in plasma on laser-supported absorption (LSA) wave regime and sample composition. The laser-supported combustion (LSC) and laser-supported detonation (LSD) wave dominated plasmas with different elemental mass ratios are induced from a series of binary immiscible alloys by using low and high irradiance laser pulses, respectively. By comparing the spatial-temporal emissivity images of species, the following conclusions are drawn: 1) laser irradiance can change the species distribution of plasma, while the sample composition cannot; 2) for LSC-wave dominated plasma, the species distribution mainly depends on the melting points of constituted elements in the sample, while for LSD-wave dominated plasma, it mainly depends on the atomic masses of elements. The above behaviours on species distribution in plasma produced from binary immiscible alloys are expected to be suitable for other elements or even multi-element plasmas.

Modeling the Laser Energy Supply in a Gas Flow

The results of numerical modeling of laser energy supply in a supersonic flow are presented. In contrast to the common approach, in the new calculation model, not only the absorbed power is taken into account, but also the plasma breakdown impulse in the domain of emission focusing does. The value of the impulse is determined using the model of radiation absorption behind the front of the laser-supported detonation wave. An analysis of the results is presented.

Моделирование лазерного энергоподвода в газовый поток

AbstractThe results of numerical modeling of laser energy supply in a supersonic flow are presented. In contrast to the common approach, in the new calculation model, not only the absorbed power is taken into account, but also the plasma breakdown impulse in the domain of emission focusing does. The value of the impulse is determined using the model of radiation absorption behind the front of the laser-supported detonation wave. An analysis of the results is presented.

Direct numerical simulation of laser induced breakdown and the associated micro-cavitation in a bio-tissue

An integrated analysis of laser induced breakdown (LIB) and the associated micro-cavitation in a water-like bio-tissue is developed in this study. With this integrated analysis using minimum experimentally fitted parameters, threshold energies of LIB in bio-tissue under different numerical apertures of the focusing lenses can be determined, which provides similar values as the corresponding experimental measurements. The integrated analysis can also determine the electron temperature and number density when LIB is triggered, which also fall in the same order as the corresponding experimental measurements. In addition, the rapid size increment of plasma plume through laser supported detonation wave during a LIB can be observed with the integrated analysis. The developed integrated analysis becomes unstable when strong pressure wave presents due to strong heating and the following rapid expansion of the bio-tissue under higher input laser energy (compared with the threshold energy of LIB). Therefore, for simulating high energy LIB and the following micro-cavitation in a bio-tissue, a more advanced numerical scheme that can better capture the propagation of pressure wave will be required in the future.

Mode transition of plasma expansion for laser induced breakdown in Air

High-speed shadowgraph visualization experiments conducted using a 10 J pulse transversely excited atmospheric (TEA) CO2 laser in ambient air provided a state transition from overdriven to Chapman–Jouguet in the laser-supported detonation regime. At the state transition, the propagation velocity of the laser-supported detonation wave and the threshold laser intensity were 10 km/s and 1011 W/m2, respectively. State transition information, such as the photoionization caused by plasma UV radiation, of the avalanche ionization ahead of the ionization wave front can be elucidated from examination of the source seed electrons.

Accurate propagation velocity measurement of laser supported detonation waves

One dimensional experimental data of a Laser Supported Detonation (LSD) wave is necessary for validation of the LSD propagation model. In this study, a LSD was driven in a pulsed CO2 laser beam whose equivalent diameter was 7.2 mm, which was sufficient to neglect lateral enthalpy dissipation in comparison with laser energy input. In order to evaluate this relation, an identical LSD wave propagation velocity was obtained with and without lateral flow confinement by a solid wall. In addition, accurate prediction of the LSD propagation velocities were obtained. These were same in a beam of 5.1 mm diameter while it was about twice as high as in a beam of 1.2 mm diameter. In the high laser intensity region, the LSD propagation velocity was higher than that of Chapman-Jouguet condition.

Morphology and characteristics of laser-induced aluminum plasma in argon and in air: A comparative study

In laser-induced breakdown spectroscopy (LIBS), ablation takes place in general in an ambient gas of the atmospheric pressure, often in air but also in noble gas such as argon or helium. The use of noble gas is known to significantly improve the performance of the technique. We investigate in this work the morphology and the characteristics of induced plasma in argon and in air. The purpose is to understand the mechanism of the analytical performance improvement by the use of argon ambient with respective to air ambient and the dependence on the other experimental parameters such as the laser fluence. The observation of plasma morphology in different ambient gases provides also information for better design of the detection system which optimizes the signal collection according to the used ambient gases. More specifically, the expansion of the plasma induced on an aluminum target with nanosecond infrared (1064nm) laser pulse in two ambient gases, argon and the atmospheric air, has been studied with spectroscopic imaging at short delays and with emission spectroscopy at longer delays. With relatively low ablation laser fluence (65J/cm2), similar morphologies have been observed in argon and in air over the early stage of plasma expansion, while diagnostics at longer delay shows stronger emission, higher electron density and temperature for plasma induced in argon. With higher ablation laser fluence (160J/cm2) however, different expansion behaviors have been observed, with a stagnating aluminum vapor near the target surface in air while a propagating plume away from the target in argon. The craters left on the target surface show as well corresponding difference: in air, the crater is very shallow with a target surface chaotically affected by the laser pulse, indicating an effective re-deposition of the ablated material back to the crater; while in Ar a deeper crater is observed, indicating an efficient mass removal by laser ablation. At longer delays, a brighter, denser and hotter plasma is always observed in argon than in air as with lower ablation laser fluences. The observed different influences of the ambient gas on the plasma expansion behavior for different laser fluences are related to the different modes of laser-supported absorption waves, namely laser-supported combustion (LSC) wave and laser-supported detonation (LSD) wave.

Light detonation wave in a cylindrical Z-pinch

A secondary compression wave previously observed by other researchers in a cylindrical Z-pinch has been identified in this work as a light detonation wave. It appears on the inner surface of a discharge chamber under the action of the intense ultraviolet radiation from a plasma pinch at the stage of its maximum compression. The condition of the light detonation wave has been determined experimentally. The dependence of its Mach number on a generalized dimensionless variable has been determined taking into account the conservation laws for the light detonation wave including the pressure of the gas, expenses on the formation of the surface plasma, and the energy of ionization of the gas involved in the wave. An analogy with the laser-supported detonation wave created by intense laser radiation has been revealed. The indicated dependence is within the error of measurement in agreement with the experimental data for light detonation waves created by both methods.

Predicting propagation limits of laser-supported detonation by Hugoniot analysis

Termination conditions of a laser-supported detonation (LSD) wave were investigated using control volume analysis with a Shimada–Hugoniot curve and a Rayleigh line. Because the geometric configurations strongly affect the termination condition, a rectangular tube was used to create the quasi-one-dimensional configuration. The LSD wave propagation velocity and the pressure behind LSD were measured. Results reveal that the detonation states during detonation and at the propagation limit are overdriven detonation and Chapman–Jouguet detonation, respectively. The termination condition is the minimum velocity criterion for the possible detonation solution. Results were verified using pressure measurements of the stagnation pressure behind the LSD wave.

Calculation of laser induced impulse based on the laser supported detonation wave model with dissociation, ionization and radiation

In the laser intensity range that the laser supported detonation (LSD) wave can be maintained, dissociation, ionization and radiation take a substantial part of the incidence laser energy. There is little treatment on the phenomenon in the existing models, which brings obvious discrepancies between their predictions and the experiment results. Taking into account the impact of dissociation, ionization and radiation in the conservations of mass, momentum and energy, a modified LSD wave model is developed which fits the experimental data more effectively rather than the existing models. Taking into consideration the pressure decay of the normal and the radial rarefaction, the laser induced impulse that is delivered to the target surface is calculated in the air; and the dependencies of impulse performance on laser intensity, pulse width, ambient pressure and spot size are indicated. The results confirm that the dissociation is the pivotal factor of the appearance of the momentum coupling coefficient extremum. This study focuses on a more thorough understanding of LSD and the interaction between laser and matter.