ICCD Imaging Research Articles

Spatio-temporal development of microdischarges in a surface barrier discharge arrangement in air at atmospheric pressure

The spatio-temporal development of single microdischarges in an asymmetric surface barrier discharge arrangement was investigated. The arrangement consisted of two needle electrodes laid on a dielectric plate. The discharge was operated in dry air at atmospheric pressure with a sinusoidal applied voltage. The discharge was investigated by current-voltage measurements as well as two optical techniques, the intensified CCD imaging (equipped with a far-field microscope) and the cross-correlation spectroscopy. While the combined methods of iCCD imaging and far-field microscope recorded two-dimensional pictures with a high spatial resolution, the CCS recorded the spatio-temporal development of the luminosity of the 0–0 transitions of the second positive system (λ = 337.1 nm) and first negative system (λ = 391.5 nm) of molecular nitrogen. The intensities of these two bands were measured with a fine spatial and temporal resolution. It was found that both half periods have significant differences in the mechanism. While the positive half period behaves similar as volume or coplanar barrier discharges, during the negative half period no positive streamer was detected.

Pure rotational CARS studies of thermal energy release and ignition in nanosecond repetitively pulsed hydrogen-air plasmas

Pure rotational CARS thermometry, complemented by UV emission measurements and ICCD imaging, is used to study kinetics of low temperature plasma assisted fuel oxidation and ignition in a repetitive nanosecond pulse discharge in hydrogen-air mixtures, with number of pulses in a 40 kHz burst varying from a few to a few hundred. Time-resolved OH emission, coupled with gated ICCD images of the plasma and the flame, demonstrate that volumetric ignition of H 2–air mixtures occurs in a spatially uniform plasma. The results are shown to agree well with predictions of a new hydrogen-air plasma chemistry model, which incorporates non-equilibrium plasma processes, H 2–air chemistry, non-empirical scaling of nanosecond pulse energy coupled to the plasma, and quasi-one-dimensional conduction heat transfer. In particular, the results demonstrate that the heating rate in low temperature hydrogen-air plasmas is much faster than in air plasmas, primarily due to energy release from exothermic reactions of fuel with O and H atoms generated in the plasma. Kinetic sensitivity analysis is used to identify dominant plasma and chemical processes of hydrogen oxidation, demonstrating that additional heat release in these reactions is a key factor in ignition kinetics. Kinetic modeling calculations demonstrate that removal of the radical generation processes by the nanosecond pulsed plasma from the model completely blocks subsequent exothermic chemical reactions, thus making ignition impossible.

Al2O3 ceramics under high-fluence irradiation: plasma plume dynamics through space- and time-resolved optical emission spectroscopy

The dynamics of a transient laser ablation plasma plume has been investigated by means of space- and time-resolved optical emission spectroscopy (OES), through a high-resolution monochromator and a fast gate ICCD camera. The experiments have been carried out with the third harmonic (355 nm) of a Q-switched (10 ns) Nd:YAG laser focused on Al2O3 samples placed in a vacuum chamber (10−7 Torr). The splitting of the plasma plume into two components has been evidenced by ICCD imaging. In the OES study, Al and O neutral atoms and different charge state ions have been monitored through the evolution of selected spectral lines. The two plume components (fast and slow) are found to consist mainly of charged and neutral species, respectively. Fundamental parameters of these species (e.g. excitation temperature) have been derived.

The effects of hump electrode on the long gap plasma display panel with high Xe concentration ratio

It was reported that a plasma display panel with hump electrode in the long gap has improved discharge characteristics such as luminous efficacy, addressing jitter than long gap electrode structure. In this paper, as an extended study of previous work, we report properties of long gap discharge with hump electrode for various Xe concentration ratio in a Ne–Xe binary gas mixture. Due to the hump electrodes between long gap, discharge voltage is reduced by 20–30 V and high luminous efficacy is obtained at low voltages in high Xe percentage. For more detailed observation of discharge, ICCD images of infrared light emission from excited Xe in discharge cell are taken. The results show that the discharge is initiated between short gap of hump electrodes and the main part of the discharge is maintained between long gap electrodes. In addition, 3-dimensional simulation study shows that hump electrode shape has higher number of excited Xe and Xe 2 than the conventional one. This is well correlated with the experimental result showing higher luminance in the hump structure.

Diagnostics of plasma plume produced by laser ablation using ICCD imaging and transient electrical probe technique

The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been investigated by means of fast ICCD imaging and electrical probes in transient regime. Measurements have been carried out on plasmas produced in vacuum (5× 10−6 Torr residual pressure) by a pulsed Excimer laser (20 ns, XeCl, λ= 308 nm) irradiating stainless steel targets. Two plasma expansion velocities were estimated, one from probe measurements and another from recorded ICCD images. Electron plasma temperature (0.1 − 0.3 eV) and density (1 − 5×1011 cm−3) were measured by electrical probes for a laser radiation power density of 6×108 W/cm2.

Experimental Study of a Compact Nanosecond Plasma Gun

AbstractThe paper presents a new discharge plasma setup, called plasma gun, allowing the generation of nanosecond duration plasma bullets from a pulsed dielectric barrier discharge reactor. These bullets propagate at very high velocity, up to 5 × 108 cm · s−1, in flexible dielectric capillaries flushed with neon or helium flow rates as low as 100 mL · min−1, over distances of a few tens of centimetres, before inducing plasma plume formation in ambient air. Time resolved nanosecond ICCD imaging show evidence for the channelled structure of the bullets which propagate along the inner surface of the dielectric guide. A few centimetres from the DBD reactor where they are generated, the plasma bullets expand with no connection to the high voltage power source. Non‐thermal air plasma plume production is described by spectroscopic measurements. The plasma gun is likely to be developed for remote high voltage fast commutation or in plasma medicine applications or for the decontamination of small diameter catheters.magnified image

Nanoparticles and Thin Film Formation in Ultrashort Pulsed Laser Deposition of Vanadium Oxide

The ultrashort pulsed laser deposition of vanadium oxide thin films has been carried out by a frequency-doubled Nd:glass laser with a pulse duration of 250 fs. The characteristics of the plasma produced by the laser-target interaction have been studied by ICCD imaging and optical emission spectroscopy. The results confirm that an emitting plasma produced by ultrashort laser pulses is formed by both a primary and a secondary component. The secondary component consists of particles with a nanometric size, and their composition and spatial angular distribution influence the deposited films. In fact, these films, analyzed by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and atomic force microscopy, are formed by the aggregation of a large number of nanoparticles whose composition is explained by a model based on equilibrium thermal evaporation from particles directly ejected from the target. On these basis, the presence in the films of a mixture of V(2)O(5) and VO(2) is discussed.

Laser-induced plasma study by fast imaging for Sm1−x Nd x NiO3 thin film deposition

In this paper, the plume expansion dynamics of an ablated Sm2O3, Nd2O3 and NiO mixture oxides target by KrF laser into background oxygen atmosphere has been investigated using a fast ICCD imaging. The laser fluence was fixed at 2 J cm−2 and the surrounding ambient gas pressure was varied from vacuum to 50 mbar. Some effects as double plume splitting, plume sharpening and plume stopping were observed. The imaging data were used to create position–time plots of the luminous front. The plume behaviour was found to be influenced by the gas pressure above a certain threshold. Exceeding this pressure threshold, in earlier time the expansion was almost linear independently of the background gas pressure used. However, as time evolves, the plume is decelerated and comes to rest. The plasma plume dynamics was analysed in the framework of a shock-wave model and a drag model. It was found that the shock-wave model is valid in distances range which depends on the gas pressure. At later time, it is rather the drag model which is valid since it predicts exactly the stopping distance observed at high pressures. Using the dimensionless variables, a general description of the plasma plume dynamics was given. Finally, the plasma plume width-time evolution was studied.

Investigation of the Pb Depletion in Single and Dual Pulsed Laser Deposited Epitaxial PZT Thin Films and Their Structural Characterization

AbstractWe have investigated the Pb depletion in laser ablated PZT (PbZr0.52Ti0.48O3) films through a systematic study of PZT target-laser interactions for both single laser and dual-laser ablation methods. The study includes films deposited from a stoichiometric and an excess PbO PZT targets. The films were deposited on single crystal SrTiO3[100] substrates at 550˚C with a background oxygen pressure of 500 mT. Single laser deposited films at a laser fluence of 5J/cm2 produced the highest Pb content while dual-laser ablated films where an excimer and a CO2 pulsed lasers were synchronized for ablation produced high Pb content for an excimer laser fluence of less than 2J/cm2. This enabled the growth of particulate-free PZT films with high Pb content. ICCD imaging of the plasma plumes showed variations in the expansion profiles at different laser fluencies that correlated well with the Pb content observed in the deposited films.

Enhancement in Ferroelectricity in V-Doped ZnO Thin Film Grown using Laser Ablation

AbstractWe report evidence of enhancement in ferroelectricity in thin films of vanadium (V) doped ZnO grown at higher oxygen pressure. This process reduces oxygen deficiency and the material becomes very insulating, which in turn lowers the leakage current through the ferroelectric capacitor. 2 at. % V doped ZnO films, with thickness of approximately 1 μm were grown epitaxially on c-cut sapphire (Al2O3) (0001) at a growth temperature of 600°C. X-ray analysis showed the layers to be epitaxial where the (0002) diffraction peak had a rocking curve FWHM below 1°. The films with higher oxygen pressure were more insulating than the one grown with lower oxygen pressure. The saturation polarization doubled when the growth pressure increased from 300 mT to 500 mT. Time gated ICCD imaging of the ablated plasma during various O2 pressures and how it translated to the film quality are presented.

Analysis of streamer properties in air as function of pulse and reactor parameters by ICCD photography

Streamer properties such as their velocity, diameter, intensity and density, can be obtained by analysis of temporal and spatial resolved ICCD imaging. In this paper, experimental results on streamer generation and propagation as a function of several high-voltage pulse and reactor parameters are described. Experiments were performed on a large scale wire–plate reactor in ambient air. The set-up allows for independent variation of the parameters over wide ranges. The minimum gate time of the ICCD camera is 5 ns, allowing for a high temporal resolution. The camera can be triggered with a precision of 1 ns. Both negative and positive polarity pulses are investigated. The most important conclusions are as follows. (1) The streamer velocity ((0.5–2.5) × 106 m s−1) increases if the applied electric field and/or the voltage rise rate is increased. (2) The same is true regarding the velocity ((0.2–1.2) × 105 m s−1) with which the streamer diameter (0.7–3.0 mm) increases during propagation. (3) Typical properties (velocity, diameter, etc) of negative and positive polarity streamers vary less than 25%, especially when the applied electric field is high. (4) As long as the dc bias voltage is below the dc corona onset value it does not have a separate effect on the visual streamer properties. Only the total voltage (peak voltage + dc) is of importance. (5) A simple model was used to determine the electric field in the secondary streamer channel. It was found that in the light emitting part of the secondary streamer the electric field is approximately 21.5 kV cm−1. In the remainder (dark part) of the channel the electric field is around 6.5 kV cm−1. This paper shows mainly experimental findings. Not all observed relations and phenomena could be explained. This is partly caused by the fact that current theoretical and numerical models are not yet able to describe the experimental situation as used during this study.

Space- and time-resolved optical diagnosis for the study of laser ablation plasma dynamics

The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been investigated by means of optical methods (time- and space-resolved emission spectroscopy and fast ICCD imaging). Systematic measurements have been carried out on plasma produced in vacuum (10−8Torr residual pressure) by Nd:YAG laser (10ns, 532nm) irradiation of Aluminum targets. Al neutral atoms and different charge state ions have been monitored through the evolution of corresponding spectral lines. The study evidenced the presence of two different groups of particles, tentatively related to two distinct ejection mechanisms. This behavior has been confirmed by the fast ICCD (20ns gate) recording of the total optical emission of the plume. The application of the relative line intensity method to the study of the excitation temperature axial profile is equally discussed.

Dynamics of a pulsed-electron beam induced plasma: application to the growth of zinc oxide thin films

Spatial and temporal distributions of species emitted from ablation of zinc oxide target by a pulsed-electron beam are studied by the complementary use of optical emission spectroscopy and camera fast imaging. We show that the slowest electrons produced by the accelerating tube in the pulsed-electron beam deposition (PED) system interact with the plasma plume and involve a further excitation of the neutrals species. The velocities of atoms and ions are found to be similar to those obtained in the well-known pulsed-laser deposition (PLD) process while the plasma temperature and the electron density are lower. The low absorption of the electron beam by the expanding plasma compared with that experienced in PLD leads to a higher removal of ablated material and consequently to a higher deposition rate ten times greater than in PLD. The PED ZnO films grown at room temperature on silicon substrate are constituted by the stacking of small aggregates without large macroscopic droplets. These results are in agreement with the ICCD images recorded at long time delays from the electron impact which do not evidence bright trails correlated with the propagation of slow and large particles.

ICCD Imaging of Coexisting Arc Roots and Arc Column in a Large-Area Dispersed Arc-Plasma Source

Arc attachments to cathode, as well as to anode, had been investigated with the bulk arc plasma between the coaxial electrodes with short-exposure-time ICCD imaging. The images captured suggests that multiple cathodic spots and diffuse attachment to the anode and cathode might contribute to the stability of rotating annular plasma dispersed by strong external coaxial magnetic field.

Nanosecond-Discharge Development in Long Tubes

High-voltage nanosecond discharge at moderate pressures develops in the form of a fast ionization wave. High electric field in the discharge front produces high-energy electrons and supports uniform preionization. The discharge creates spatially uniform and highly nonequilibrium plasma with dominant excitation of the high-energy electronic levels during tens and hundreds of nanoseconds. The development of the discharge is traced using the emission of the second positive system of molecular nitrogen. ICCD images of the discharge development and propagation in air are presented.

Formation and Expansion Phases of an Atmospheric Pressure Glow Discharge in a PECVD Reactor via Fast ICCD Imaging

This paper reports on the experimental study of the dynamic evolution of a dielectric barrier discharge in an atmospheric-pressure plasma enhanced chemical vapor deposition reactor using a gated intensified charge coupled detector. It is observed that a diffuse atmospheric pressure glow is formed via transition from Townsend-like discharge or, alternatively, can be initiated by a filamentary discharge. The formation of the glow current spot is followed by the lateral expansion of the discharge.

Investigation of a Novel Large Area Dispersed Arc Plasma Source With Time-Resolved ICCD Imaging

Unsaturated time-resolved end-on images of argon arc plasma at 1 atm were captured by an intensified charge-coupled device equipped with a narrowband interference filter to evidence the homogeneity of the arc plasma dispersed by increasing the axial magnetic field. A relatively uniform diffuse current sheet was identified established between the concentric electrodes of our specified experimental geometry.

Evolution of Cathodic Arc Roots in a Large-Scale Magnetically Rotating Arc Plasma

The behavior of the cathode arc root is one of the most fundamental phenomena associated with arc discharges. The formation of isolated multiple cathodic roots and the transition from discrete spots to a diffuse cathodic attachment in an argon arc plasma at 1 atm have been observed with short exposure time ICCD imaging in our attempt to generate a uniform large-area plasma, using magnetically rotating arc plasma.

Mechanisms of deflagration-to-detonation transition under initiation by high-voltage nanosecond discharges

An experimental study of detonation initiation in a stoichiometric propane–oxygen mixture by a high-voltage nanosecond gas discharge was performed in a detonation tube with a single-cell discharge chamber. The discharge study performed in this geometry showed that three modes of discharge development were realized under the experimental conditions: a spark mode with high-temperature channel formation, a streamer mode with nonuniform gas excitation, and a transient mode. Under spark and transient initiation, simultaneous ignition inside the discharge channel occurred, forming a shock wave and leading to a conventional deflagration-to-detonation transition (DDT) via an adiabatic explosion. The DDT length and time at 1 bar of initial pressure in the square smooth tube with a 20-mm transverse size amounted to 50 mm and 50 μs, respectively. The streamer mode of discharge development at an initial pressure of 1 bar resulted in nonuniform mixture excitation and a successful DDT via a gradient mechanism, which was confirmed by high-speed time resolved ICCD imaging. The gradient mechanism implied a longer DDT time of 150 μs, a DDT run-up distance of 50 mm, and an initiation energy of 1 J, which is two orders of magnitude less than the direct initiation energy for a planar detonation under these conditions.

Laser irradiation effects on gold

Investigations on the laser irradiation effects on gold are explored in terms of plasma-plume dynamics and morphological and crystallographic changes. Annealed 4N gold samples were irradiated with a Q-switched Nd:YAG laser (53 mJ, 21 MW, 532 nm, and pulse width 6–8 ns) for plume dynamics using 10-ns gated fast photography. A Q-switched pulsed Nd:YAG laser (10 mJ, 1.1 MW, 1064 nm, and pulse width 9 ns) was used to irradiate the surface of the samples for morphological and crystallographic studies of laser-irradiated gold in a vacuum ∼10−3 Torr. The annealed samples were exposed to 50 shots of a Nd:YAG laser (10 mJ, 1.1 MW, 1064 nm, and pulse width 9 ns). The investigation on the plume was done by using an intensified charged-couple device ICCD-5760/IR-UV camera. The morphological investigation of the irradiated surface was carried out by analyzing micrographs obtained using an Hitachi S 3000 H scanning-electron microscope (SEM). The crystallographic studies of the irradiated samples were performed by analyzing the XRD patterns obtained using an X’ Pert Pro Pan Analytical X-ray diffractometer. The investigation on gated ICCD images of the plume reveal that, at very earlier times, the plasma-plume expansion has a linear trend, whereas, at later times, the plasma-plume expansion is nonuniform. SEM micrographs exhibit the primary mechanisms of pulsed-laser ablation (PLA), such as hydrodynamic sputtering, thermal sputtering, exfoliation sputtering, and splashing. The surface morphology was explained in terms of crater formation, swelling, burning, nucleation, grain growth, and nonsymmetric heat conduction. The nonuniform thermal expansion of gold due to thermal-energy transfer is also studied by SEM micrographs, which was supported by XRD analysis. The structural analysis on the basis of XRD shows that the composition of the irradiated samples is not disturbed even after laser irradiation. The grain sizes also changed due to laser irradiation.