Laser-induced Discharge Research Articles

Effective methane decomposition using spark discharge assisted laser-induced plasma: An approach based on Fourier transform infrared (FTIR) spectroscopy

The widespread utilization of fossil fuels cause to significantly elevate greenhouse gas emissions. Consequently, the developments of the innovative methods are essential to convert methane into the green energy. Recently, significant effort is made to enhance the performance of the plasma-based conversion technologies. Here, the dissociation rate of methane into heavier hydrocarbon compounds are carefully determined by making use of a hybrid laser-induced plasma (LIP) and spark discharge (SD). Fourier-transform infrared (FTIR) spectroscopy reveals a couple of characteristic peaks after laser triggering, whose intensities notably increase at higher applied voltages. The corresponding peaks indicate the formation of heavier compounds including sp and sp2 C–H stretching bonds. The findings elucidate that the methane decomposition rate notably elevates in favor of hybrid SD-LIP against that of traditional LIP. It is worth noting that the simultaneous ablative effect of the catalyst surface to remove the carbon soot by the successive laser shots could prevent the catalytic deactivation leading to the sustained performance.

Simulation of extreme ultraviolet radiation of laser induced discharge plasma

Extreme ultraviolet (EUV) light source is an important part of EUV lithography system in semiconductor manufacturing. The EUV light source requires that the 4p<sup>6</sup>4d<sup><i>n</i></sup>-4p<sup>5</sup>4d<sup><i>n</i>+1</sup> + 4d<sup><i>n</i>-1</sup>4f transitions of Sn<sup>8+~13+</sup> ions emit thousands of lines which form unresolved transition arrays near 13.5 nm. Laser-induced discharge plasma is one of the important technical means to excite target into an appropriate plasma condition. Laser-induced discharge plasma has a simple structure and a low cost. It also has important applications in mask inspection, microscopic imaging, and spectral metrology. In the design and production process, there are many factors that can influence the conversion efficiency, such as current, electrode shape, and laser power density. The simulation method is a convenient way to provide guidance for optimizing the parameters. In this paper, a completed radiation magneto-hydrodynamic model is used to explore the dynamic characteristics of laser-induced discharge plasma and its EUV radiation characteristics. To improve the accuracy, a more detailed global equation of state model, an atomic structure calculation model including relativistic effect and a collision radiation model are proposed simultaneously. The simulation reconstructs the discharge process effectively, which is divided into five stages in the first half cycle of current, including expansion of laser plasma, column formation of discharge plasma, diffusion of discharge plasma, contraction of discharge plasma, and re-diffusion of discharge plasma. It is revealed that the pinch effect during the current rising time exerts a significant influence on the generation of EUV radiation. The conversion efficiency of EUV radiation is still low under our existing conditions, and hopefully a higher rising rate of current can improve the conversion efficiency in the future work.

Simulation of extreme ultraviolet radiation of laser induced discharge plasma

Extreme ultraviolet (EUV) light source is an important part of EUV lithography system in semiconductor manufacturing. The EUV light source requires that the 4p<sup>6</sup>4d<sup><i>n</i></sup>-4p<sup>5</sup>4d<sup><i>n</i>+1</sup> + 4d<sup><i>n</i>–1</sup>4f transitions of Sn<sup>8+~13+</sup> ions emit thousands of lines which form unresolved transition arrays near 13.5 nm. Laser-induced discharge plasma is one of the important technical means to excite target into an appropriate plasma condition. Laser-induced discharge plasma has a simple structure and a low cost. It also has important applications in mask inspection, microscopic imaging, and spectral metrology. In the design and production process, there are many factors that can influence the conversion efficiency, such as current, electrode shape, and laser power density. The simulation method is a convenient way to provide guidance for optimizing the parameters. In this paper, a completed radiation magneto-hydrodynamic model is used to explore the dynamic characteristics of laser-induced discharge plasma and its EUV radiation characteristics. To improve the accuracy, a more detailed global equation of state model, an atomic structure calculation model including relativistic effect and a collision radiation model are proposed simultaneously. The simulation reconstructs the discharge process effectively, which is divided into five stages in the first half cycle of current, including expansion of laser plasma, column formation of discharge plasma, diffusion of discharge plasma, contraction of discharge plasma, and re-diffusion of discharge plasma. It is revealed that the pinch effect during the current rising time exerts a significant influence on the generation of EUV radiation. The conversion efficiency of EUV radiation is still low under our existing conditions, and hopefully a higher rising rate of current can improve the conversion efficiency in the future work.

Nonlinear Propagation and Filamentation on 100 Meter Air Path of Femtosecond Beam Partitioned by Wire Mesh.

High-intensity (∼1 TW/cm and higher) region formed in the propagation of ∼60 GW, 90 fs Ti:Sapphire laser pulse on a ∼100 m path in air spans for several tens of meters and includes a plasma filament and a postfilament light channel. The intensity in this extended region is high enough to generate an infrared supercontinuum wing and to initiate laser-induced discharge in the gap between the electrodes. In the experiment and simulations, we delay the high-intensity region along the propagation direction by inserting metal-wire meshes with square cells at the laser system output. We identify the presence of a high-intensity region from the clean-spatial-mode distributions, appearance of the infrared supercontinuum wing, and occurrence of the laser-induced discharge. In the case of free propagation (without any meshes), the onset of the high-intensity zone is at 40–52 m from the laser system output with ∼30 m extension. Insertion of the mesh with 3 mm cells delays the beginning of the high-intensity region to 49–68 m with the same ∼30 m extension. A decrease in the cell size to 1 mm leads to both delay and shrinking of the high-intensity zone to 71–73 m and 6 m, respectively. Three-dimensional simulations in space confirm the mesh-induced delay of the high-intensity zone as the cell size decreases.

Remote triggering of air-gap discharge by a femtosecond laser filament and postfilament at distances up to 80 m

We experimentally observed laser-induced remote high-voltage discharge triggering between two needle electrodes with half-a-cm spacing. The discharge was initiated by a 744-nm, 90-fs, 6-mJ laser pulse undergoing filamentation in air. For the direct voltage below the self-breakdown threshold, triggering of air-gap discharge was synchronized with a 10-Hz laser repetition rate and occurred between 40 and 80 m of the propagation path. No discharge guiding was observed. The experimentally registered and simulated remote triggering probability was above 80% in the range of 45–60 m from laser output and about 50% in the range of 60–80 m. The probability decreases as the postfilament hot spot diverges with a simultaneous increase in stochastic laser beam wandering.

Micro-pinch formation and extreme ultraviolet emission of laser-induced discharge plasma* *Project supported by the Basic and Applied Basic Research Major Program of Guangdong Province, China (Grant No. 2019B030302003).

Extreme ultraviolet (EUV) source produced by laser-induced discharge plasma (LDP) is a potential technical means in inspection and metrology. A pulsed Nd:YAG laser is focused on a tin plate to produce an initial plasma thereby triggering a discharge between high-voltage electrodes in a vacuum system. The process of micro-pinch formation during the current rising is recorded by a time-resolved intensified charge couple device camera. The evolution of electron temperature and density of LDP are obtained by optical emission spectrometry. An extreme ultraviolet spectrometer is built up to investigate the EUV spectrum of Sn LDP at 13.5 nm. The laser and discharge parameters such as laser energy, voltage, gap distance, and anode shape can influence the EUV emission.

Elongated long-lived jet of dense plasma produced by a hollow laser beam

Numerical simulation of the dynamics of plasma jets planned for use for the initiation of vacuum pinch discharges has been carried out. Jets of the “laser-metal-plasma-liner” type are created by laser beams with different spatial intensity distributions, which irradiate targets of various configurations. The three variants of plasma-jets formation are considered: irradiation of a target by (i) a Gaussian beam from a neodymium laser, (ii) the same Gaussian beam incident on a hole in the target, and (iii) a beam with the intensity distribution of the Laguerre–Gaussian mode. The dynamics of spatial distributions of the electron density, jet plasma temperatures, and the target mass ablated by laser radiation is calculated. It is shown that for quite moderate laser beam energies and intensities ∼400 mJ and ∼109 W/cm2, respectively, in the second and third cases, jets are produced with the lifetime of a few tens of nanoseconds and the maximum density ∼1019 and 1021 cm−3, respectively. The use of such jets can increase the pinching efficiency and improve plasma parameters in laser-induced discharges.

Laser-induced liquid tin discharge plasma and its EUV spectra

Laser-induced discharge plasmas (LDPs) have the potential to be inspection and metrology sources in extreme ultraviolet (EUV) lithography. An LDP EUV source was developed to avoid tin electrode erosion in which a tin pool was used as a cathode. A CO2 pulse laser was focused on the liquid tin target surface, and then a breakdown occurred in a very short time. The voltage-current characteristics of the discharge oscillated, lasting for several microseconds, and an RLC fitting model was used to obtain the inductance and resistance. An intensified charge-coupled device (ICCD) camera was used to investigate the dynamics of LDP, which can explain the formation of a discharge channel. The EUV spectra of laser-induced liquid tin discharge plasma were detected by a grazing incident ultraviolet spectrometer, compared with a laser-produced tin droplet plasma EUV spectrum. To explain the EUV spectrum difference of laser-induced liquid tin discharge plasma and laser-produced tin droplet plasma, the collision radiation (CR) model combined with COWAN code was used to fit the experimental EUV spectrum, which can estimate the electron temperature and density of the plasma.

Discharge initiation by a laser pulse in a vacuum gap

Laser-induced discharge within a vacuum gap of few millimeters between electrodes is experimentally studied. The discharge is triggered by 1064 nm Nd:YAG laser pulses with intensities varied from 107 W/cm2 to 109 W/cm2 on the surface of target electrode The current formation time dependences from both the gap length and the residual gas pressure at a fixed electrode voltage were determined. Residual gas pressure varied from 10−6 to 10−2 torr, and voltage varied from 100 V to 5 kV. The dependences of current formation time on the laser pulse intensity and the voltage difference on the electrodes of different polarity are presented. The laser intensity thresholds for discharge are determined in our experimental conditions. We also performed atomistic and hydrodynamics modeling of laser heating and evaporation of metal from electrode surface. The experimental and modeling results are used for development of qualitative mechanism of ionization and charge multiplication processes in metal vapor.

Emission of a low-power laser-induced vacuum discharge plasma in the EUV and SXR spectral ranges

X-ray spectral characteristics of a vacuum discharge plasma with the storage energy lower than 30 J initiated on an Al or a Fe cathode by a 1012 W/cm2 neodymium laser were studied in the 30 – 300 Å wavelength range. It is shown that both the spectral composition and intensity of radiation of a micropinch plasma produced in the cathode jet of the discharge are determined by parameters of the discharge and laser pulse. These parameters were optimized to achieve a regime in which a considerable part of radiation energy was concentrated in the long-wavelength band of the quasi-continuum (230 - 270 Å and 160 - 200 Å for Al and Fe, respectively), which makes this discharge a source of narrowband X-ray radiation.

Long-lived laser-induced arc discharges for energy channeling applications

Laser filamentation offers a promising way for the remote handling of large electrical power in the form of guided arc discharges. We here report that it is possible to increase by several orders of magnitude the lifetime of straight plasma channels from filamentation-guided sparks in atmospheric air. A 30 ms lifetime can be reached using a low-intensity, 100 mA current pulse. Stability of the plasma shape is maintained over such a timescale through a continuous Joule heating from the current. This paves the way for applications based on the generation of straight, long duration plasma channels, like virtual plasma antennas or contactless transfer of electric energy.

Effect of Ambient Electrons on Primary Discharge Energy in Laser-Induced Discharge

We examined the laser-induced discharge (LID) in medium-vacuum air. The time-averaged discharge energy W d of a primary discharge prior to an arc discharge was affected by the number of initial electrons. The initial electrons were produced by the laser irradiation of electrodes. The number of electrons was proportional to the energy of the laser, L p . Thus, it was adjusted by changing L p . Although the experimental conditions were rather limited, i.e., air at 200-Pa pressure, we demonstrated a simple relationship, $\text{W}_{d}\propto \,\,\text{V}_{s}^{2} \times \,\,\text{L}_{p}^{s}$ , where V s is the applied voltage and s is an exponent determined empirically. Note that the number of initial electrons is a function of L p . Such a simple relationship for the behavior of LID that incorporates W d is proposed for the first time in this paper.

Features of the Growth Dynamics of Plasma Jets in Laser-Induced Vacuum Discharges with High Rates of Current Rise

An experimental study of the dynamics of formation of plasma jets and ion beams in laser-induced low-voltage discharges with high rates of current rise has been performed. It has been found that for given discharge characteristics (energy store voltage, discharge current, current rise rate, and discharge gap spacing) there exist optimum initial conditions, determined by the characteristics of the laser radiation, that provide stable single pinching of the cathode plasma jet at its maximum compression. Increasing the ion density and decreasing the temperature of the foreplasma by reducing the laser radiation power density at the cathode due to an increase in laser pulse duration improves the stability of the plasma pinching at a lower energy input.

Laser-Induced Discharge Propagation Velocity in Helium and Argon Gases

Laser-Induced Discharge Propagation Velocity in Helium and Argon Gases

On the Features of X-Ray Emission of a Laser-Plasma Diode

The formation of micropinches and X-ray sources in low-voltage, laser-induced discharges with high rates of current rise is investigated.

Dual-pulse laser-induced spark ignition and flame propagation of a methane diffusion jet flame

An experimental investigation was performed to study the ignition and flame propagation behaviors of a methane diffusion jet flame (Re= 5500) when dual pulse laser-induced spark discharges were introduced in a mixing layer. Time intervals (dt) of 50ns, 100µs, and 600µs between two laser pulses were tested, and the results were compared to a single pulse discharge case with the same total laser energy (60mJ). The laser-induced breakdown was introduced to the mixing layer at 9.5 jet diameters downstream from the jet exit. The chemical delay time scale under the flow condition was approximately 350µs (tcd). The disturbances in density fields generated by laser-induced breakdowns and chemical reactions were visualized using a high-speed schlieren imaging technique. The visualization at stationary air showed that interactions between two laser-induced breakdowns increased the surface area of hot plumes, but the effects of the interactions diminished when the breakdowns were introduced in a non-reacting air jet. The effects of the flow on the hot plumes prevailed the interaction effects between two breakdowns in non‐reacting air jet condition. However, when the dual pulse laser-induced spark discharges (dt= 600µs, dt/tcd= 1.71) were generated in a mixing layer of a methane jet, a rapid propagation of the flame was observed since the second breakdown enlarged the ignition kernel surfaces generated by the first breakdown. The results showed that using the dual pulse with intervals shorter than the electron lifetime scale (under 200ns) or longer than the chemical delay time scale could be beneficial in enhancing ignition and flame propagation processes due to the increased energy deposition or hot surface area, respectively.

Observation of micropinch formation in cathode jet of a low-power laser-induced vacuum discharge

The report presents the results from experimental investigation of micropinch formation in the plasma of a vacuum discharge induced by a 6 ns laser pulse of energy J = 0.5–200 mJ (at a storage voltage from 4 to 15 kV and the discharge current range of 6–26 kA, respectively). The discharge gap images were obtained using a pinhole camera in the EUV and soft X-ray ranges of 15–73 eV and 80–284 eV energy. It is shown that micropinch formation in the plasma cathode jet occurs, mainly, in the matter evaporated by the laser pulse at the discharge ignition near the moment when the current derivative reaches the maximum. It is found that the cathode jet may consist of several pinched areas, and each of them has its own structure, and the improvement of the discharge and laser radiation parameters allows us to reach a stable single pinching of plasma. The parameters of the micropinch (the plasma compression ratio, size, and position of the emitting area in the interelectrode gap) as well as the current flow through the interelectrode gap, at the given storage voltage, are completely governed by the laser radiation characteristics.

Formation of a cathode plasma jet in a laser-induced vacuum discharge

The process of formation of micropinch structures in the plasma of a vacuum discharge initiated by a laser pulse on the cathode is studied. It is demonstrated that the micropinch formation takes place mainly in the substance evaporated by the laser pulse upon the discharge initiation. The size of the hot region of the plasma jet and the distance from the cathode to the micropinch increase with increasing laser pulse energy.

Long plasma channels and high-voltage discharges induced by strong picosecond laser pulses

The formation of long plasma channels and laser-induced high-voltage discharges are demonstrated by focusing infrared picosecond laser pulses in air. Based on measurements of the channel conductivity, the maximum electron density in excess of 1014 cm−3 is estimated. The plasma channels are good conductors, through which long-air-gap high-voltage discharges are triggered. The breakdown voltages show large drops but the discharging paths are not well guided: in this, the plasma spots distributed along the channel might play an important role.

Simulation of small space debris impact inducing discharge using laser-induced plasma method

Small space debris impact that induces discharge can trigger disturbance of a spacecraft, which is a big threat to the safety of it. Research on this effect has already been carried out, but due to the limit of the facilities the research is also restricted. Since the primary cause of small space debris impact that induces discharge is to induce the plasma, similar to the laser inducing the plasma, this paper tries to simulate the space debris impact inducing discharge using a laser-induced discharge method. The analysis and experimental results are given, and they prove that this method is reliable.