Terahertz(THz)wave generation from laser-induced air plasma generally requires a short temporal laser pulse.In contrast,it was observed that THz radiation from ionized liquid water prefers a longer pulse,wherein the m...Terahertz(THz)wave generation from laser-induced air plasma generally requires a short temporal laser pulse.In contrast,it was observed that THz radiation from ionized liquid water prefers a longer pulse,wherein the mechanism remains unclear.We attribute the preference for longer pulse duration to the process of ionization and plasma formation in water,which is supported by a numerical simulation result showing that the highest electron density is achieved with a subpicosecond pulse.The explanation is further verified by the coincidence of our experimental result and simulation when the thickness of the water is varied.Other liquids are also tested to assure the preference for such a pulse is not exclusive to water.展开更多
Electromagnetic(EM) field is a consequence of the plasma generation induced by shock waves generated in impacts and explosions and is an important topic of study in aerospace and geophysics. Experimental research is f...Electromagnetic(EM) field is a consequence of the plasma generation induced by shock waves generated in impacts and explosions and is an important topic of study in aerospace and geophysics. Experimental research is frequently used to investigate the plasma generation in hypervelocity impacts and the EM wave emitted in chemical explosions. However, the basic plasma generation mechanism leading to the EM emission generated by the shock waves in chemical explosions is rarely studied.Therefore, a detailed investigation is performed to determine the state of the plasmas generated by the shock waves in air blast. In addition, a multi-component ionization model was improved to evaluate the ionization state of the generated plasmas. The proposed ionization model was combined with an AUSM+-up based finite volume method(FVM) to simulate the plasmas generated in the air blast. Two typical cases of simulation were carried out to investigate the relation between the shock waves and ionization, as well as the influence of ground reflection on the ionization state. It was found that the ionization zone was close behind the shock front in the air and propagates along with the shock waves. The interaction between the original shock waves and reflected shock waves was found to have a great impact of the order of 2–3 magnitudes, on the degree of ionization of the plasmas generated by the shock waves. This phenomenon explains the observation of additional EM pulses generated by ground reflection, as explored in the reference cited in this paper.展开更多
Generation characteristics of vacuum discharge plasma are very important for the applied research of metal plasma. The vacuum discharge electrode configuration and the cathode material affect the generation characteri...Generation characteristics of vacuum discharge plasma are very important for the applied research of metal plasma. The vacuum discharge electrode configuration and the cathode material affect the generation characteristics of the metal plasma which consists of metal ions coming from cathode and generated by vacuum discharge. In this research, the generation characteristics of the metal plasma generated by vacuum discharge are discussed for four patterns of electrode configurations, i.e. cone-mesh electrode setup, cone-cross line electrode setup, cone-line electrode setup and cone-ring electrode setup. Characteristics of the metal plasma, such as elec- tron density, electron temperature, space potential, ion energy, are measured by the probe method for discussing the impacts of different electrode configurations on the density of generated metal plasma. Moreover, the diffusion velocities of the metal plasma are measured for cathode materials of Pb, Al, and Cu, respectively. The experimental results indicate that the plasma generated by the discharge of cone-ring electrode configuration possesses the maximum density and the metal plasma generated by the Al cathode possesses the fastest diffusion velocity and the highest kinetic energy.展开更多
Developing efficient and robust terahertz(THz)sources is of incessant interest in the THz community for their wide applications.With successive effort in past decades,numerous groups have achieved THz wave generation ...Developing efficient and robust terahertz(THz)sources is of incessant interest in the THz community for their wide applications.With successive effort in past decades,numerous groups have achieved THz wave generation from solids,gases,and plasmas.However,liquid,especially liquid water has never been demonstrated as a THz source.One main reason leading the impediment is that water has strong absorption characteristics in the THz frequency regime.A thin water film under intense laser excitation was introduced as the THz source to mitigate the considerable loss of THz waves from the absorption.Laser-induced plasma formation associated with a ponderomotive forceinduced dipole model was proposed to explain the generation process.For the one-color excitation scheme,the water film generates a higher THz electric field than the air does under the identical experimental condition.Unlike the case of air,THz wave generation from liquid water prefers a sub-picosecond(200-800 fs)laser pulse rather than a femtosecond pulse(~50 fs).This observation results from the plasma generation process in water.For the two-color excitation scheme,the THz electric field is enhanced by one-order of magnitude in comparison with the one-color case.Meanwhile,coherent control of the THz field is achieved by adjusting the relative phase between the fundamental pulse and the second-harmonic pulse.To eliminate the total internal reflection of THz waves at the water-air interface of a water film,a water line produced by a syringe needle was used to emit THz waves.As expected,more THz radiation can be coupled out and detected.THz wave generation from other liquids were also tested.展开更多
The results of an experimental investigation of the plasma dynamics in a magnetically insu- lated ion diode in bipolar-pulse mode are presented. The experiments were done at the pulsed TEMP-4M accelerator by formation...The results of an experimental investigation of the plasma dynamics in a magnetically insu- lated ion diode in bipolar-pulse mode are presented. The experiments were done at the pulsed TEMP-4M accelerator by formation of a first negative pulse (100 ns, 150-200 kV) and a second positive pulse (80 ns, 250-300 kV). The voltage-current diode characteristics were used to analyze the plasma behavior in the anode- cathode gap. It is shown that, during the first pulse, a discrete emissive surface is formed on the graphite potential electrode and a plasma forms by explosive-emission, which before the second pulse comes, fills the whole working surface of the electrode and spreads to the anode-cathode gap. An analytical expression is obtained for the total current in the cellular structure approximation. It is shown that the current build-up for a cathode surface with dis- crete emitting centers is described satisfac- torily by a modified Child-Langmuir formula wi- th a form factor decreasing from F = 6 to 1. It is found that, once plasma formation at the gra- phite potential electrode is complete and until the second positive pulse, the plasma speed is constant and equals 1.3 ±0.2 cm/μs.展开更多
The design and the electric and emission characteristics of two handheld air plasma spray generators are presented. The plasma is generated by 60 Hz periodic discharges between two concentrically cylindrical electrode...The design and the electric and emission characteristics of two handheld air plasma spray generators are presented. The plasma is generated by 60 Hz periodic discharges between two concentrically cylindrical electrodes. A ring magnet is used to rotate arc discharges, which sprays outward by an air flow. The rotation of arc discharges keeps the generated plasma in non-equilibrium state and at relatively low temperature (<55°C). The plasma effluent yet contains high energy electrons which dissociate molecular oxygen into atomic oxygen. The emission spectroscopy of the plasma plume reveals that the plasma effluent, which carries abundant atomic oxygen, extends from the cap of the plasma spray by about 25 to 30 mm. Tests on blood droplets and smeared blood samples revealed the effectiveness and mechanism of low temperature air plasma on clotting blood. Tests on oral pathogens show that air plasma creates a zone of microbial growth inhibition in each of six treated samples, including those of grampositive bacteria and fungi, and on a cultivating biofilm sample of Streptococcus mutans UA159. The medical applications of the air plasma sprays for 1) bleeding control, 2) wound healing, and 3) dental disinfection, are then illustrated and discussed. As animal models, pigs were used in the tests of stopping wound bleeding and post-operative observation of wound healing by this air plasma spray. The results show that the bleeding from a cut to an ear artery is stopped swiftly;this air plasma spray also shortens wound healing time to about half (from 14 days to 8 days) after stopping the bleeding of a cross cut wound in the ham area. In-vitro tests demonstrate that the plasma effluent of the spray can prevent the formation of dental biofilms and further eliminate the mature biofilms.展开更多
Interest of the research in terahertz(THz)wave has been strongly motivated by its wide applications in the fields of physics,chemistry,biology,and engineering.Developing efficient and reliable THz source is of uttermo...Interest of the research in terahertz(THz)wave has been strongly motivated by its wide applications in the fields of physics,chemistry,biology,and engineering.Developing efficient and reliable THz source is of uttermost priority in these researches.Numerous attempts have been made in fulfilling the THz generation.Greatly benefited from the progress of the ultrafast pulses,the laser-induced-plasma is one of the auspicious tools to provide desirable THz waves,owing to its superiorities in high power threshold,intense THz signal,and ultrawide THz spectrum.This paper reviews the physics and progress of the THz generation from the laser-induced plasmas,which are produced by gas,liquid,and solid.The characteristics of the emitted THz waves are also included.There are many complicated physical processes involved in the interactions of laser-plasma,making various laser-plasma scenarios in the THz generations.In view of this,we will only focus on the THz generation classified by physical mechanisms.Finally,we discuss a perspective on the future of THz generation from the laser-induced plasma,as well as its involved challenges.展开更多
The resonant third-harmonic generation of a tion was investigated. Because of self-focusing self-focusing laser in plasma with a density transi- of the fundamental laser pulse, a transverse intensity gradient was crea...The resonant third-harmonic generation of a tion was investigated. Because of self-focusing self-focusing laser in plasma with a density transi- of the fundamental laser pulse, a transverse intensity gradient was created, which generated a plasma wave at the fundamental wave frequency. Phase matching was satisfied by using a Wiggler magnetic field, which provided additional angular too- mentum to the third-harmonic photon to make the process resonant. An enhancement was observed in the resonant third-harmonic generation of an intense short-pulse laser in plasma embedded with a magnetic Wiggler with a density transition. A plasma density ramp played an important role in the self-focusing, enhancing the third-harmonic generation in plasma. We also examined the ef- fect of the Wiggler magnetic field on the pulse slippage of the third-harmonic pulse in plasma. The pulse slippage was due to the group-velocity mismatch between the fundamental and third-harmonic pulses.展开更多
Single attosecond pulses can be generated when an intense laser pulse focused in a volume of a few cubic wave- lengths （λ^3） is reflected from a solid plasma surface. With relativistic two-dimensional particle-in-c...Single attosecond pulses can be generated when an intense laser pulse focused in a volume of a few cubic wave- lengths （λ^3） is reflected from a solid plasma surface. With relativistic two-dimensional particle-in-cell simulations, we investigate the effects of the incident laser intensity and the target surface profiles on attosecond pulse generation. Usually the width of the reflected attosecond pulse decreases and its electromagnetic energy density increases with increasing laser intensity, while the energy conversion efficiency to the attoseond pulse decreases, By changing the target surface profile, such as using a convex surface or adding proper preplasma, one can further shorten the attosecond pulse duration and meanwhile increase its energy density.展开更多
The application and characteristics of relatively big volume plasma produced with cathodic glow discharges taking place across a gaseous envelope over the cathode which was dipped into electrolyte in hydrogen generati...The application and characteristics of relatively big volume plasma produced with cathodic glow discharges taking place across a gaseous envelope over the cathode which was dipped into electrolyte in hydrogen generation were studied. A critical investigation of the influence of methanol concentration and voltage across the circuit on the composition and power consumption per cubic meter of cathode liberating gas was carried out. The course of plasma under-liquid electrolysis has the typical characteristics of glow discharge electrolysis. The cathode liberating gas was in substantial excess of the Faraday law value. When the voltage across the circuit was equal to 550 V,the volume of cathodic gas with sodium carbonate solution was equal to 16.97 times the Faraday law value. The study showed that methanol molecules are more active than water molecules. The methanol molecules were decomposed at the plasma-catholyte interface by the radicals coming out the plasma mantle. Energy consumption per cubic meter of cathodic gases (WV) decreased while methanol concentration of the electrolytes increased. When methanol concentration equaled 5% (-),WV was 10.381×103 kJ/m3,less than the corresponding theoretic value of conventional water electrolysis method. The cathodic liberating gas was a mixture of hydrogen,carbon dioxide and carbon monoxide with over 95% hydrogen,if methanol concentration was more than 15% (-). The present research work revealed an innovative application of glow discharge and a new highly efficient hydrogen generation method,which depleted less resource and energy than normal electrolysis and is environmentally friendly.展开更多
Spectral modulation and supercontinuum generation of a probe pulse is investigated by using the plasma grating induced by the interference of two infrared femtosecond laser pulses. The dependences of the supercontinuu...Spectral modulation and supercontinuum generation of a probe pulse is investigated by using the plasma grating induced by the interference of two infrared femtosecond laser pulses. The dependences of the supercontinuum generation from the probe pulse on the time delay, the relative polarization angle between the probe pulse and the two-pump pulses, and the input probe pulse energy are investigated. The far-field spatial profiles of the three pulses are measured with different time delays and relative polarization angle, and the core energy of the probe pulse as functions of the time delay and relative polarization angle are also shown.展开更多
Spatiotemporal optical vortex(STOV)pulses carrying purely transverse intrinsic orbital angular momentum(TOAM)are attracting increasing attention because the TOAM provides a new degree of freedom to characterize light...Spatiotemporal optical vortex(STOV)pulses carrying purely transverse intrinsic orbital angular momentum(TOAM)are attracting increasing attention because the TOAM provides a new degree of freedom to characterize light–matter interactions.In this paper,using particle-in-cell simulations,we present spatiotemporal high-harmonic generation in the relativistic region,driven by an intense STOV beam impinging on a plasma target.It is shown that the plasma surface acts as a spatial–temporal-coupled relativistic oscillating mirror with various frequencies.The spatiotemporal features are satisfactorily transferred to the harmonics such that the TOAM scales with the harmonic order.Benefitting from the ultrahigh damage threshold of the plasma over the optical media,the intensity of the harmonics can reach the relativistic region.This study provides a new approach for generating intense spatiotemporal extreme ultraviolet vortices and investigating STOV light–matter interactions at relativistic intensities.展开更多
The purpose of this study is to explore the second harmonic generation(SHG)of a high power Cosh-Gaussian beam in cold collisionless plasma.The ponderomotive force causes carrier redistribution from high field to low f...The purpose of this study is to explore the second harmonic generation(SHG)of a high power Cosh-Gaussian beam in cold collisionless plasma.The ponderomotive force causes carrier redistribution from high field to low field region in presence of a Cosh-Gaussian beam thereby producing density gradients in the transverse direction.The density gradients so produced the results in electron plasma wave(EPW)generation at the frequency of the input beam.The EPW interacts with the input beam resulting in the production of 2nd harmonics.WKB and paraxial approximations are employed for obtaining the 2nd order differential equation describing the behavior of the beam’s spot size against normalized distance.The impact of well-established laser-plasma parameters on the behavior of the beam’s spot size and SHG yield are also analyzed.The focusing behavior of the beam and SHG yield is enhanced with an increase in the density of plasma,the radius of the beam and the decentred parameter,and with a decrease in the intensity of the beam.The results of the current problem are really helpful for complete information of laser-plasma interaction physics.展开更多
The simple surface current model is extended to study the generation of high-order harmonics for a relativistic circularly polarized laser pulse interacting with a plasma grating surface. Both exact relativistic elect...The simple surface current model is extended to study the generation of high-order harmonics for a relativistic circularly polarized laser pulse interacting with a plasma grating surface. Both exact relativistic electron dynamics and optical interference of surface periodic structure are considered. It is found that high order harmonics in the specular direction are obviously suppressed whereas the harmonics of the grating periodicity are strongly enhanced and folded into small solid angles with respect to the surface direction. The conversion efficiency of certain harmonics is five orders of magnitude higher than that of the planar target cases. It provides an effective approach to generate a coherent radiation within the so-called ＇water window＇ while maintaining high conversion efficiency and narrow angle spread.展开更多
Arc reactor is the design for a compact fusion reactor.In this paper,the mechanism of an arc reactor is discussed which is a multi-isotope radio-decay cell that can be created using low energy nuclear reactor technolo...Arc reactor is the design for a compact fusion reactor.In this paper,the mechanism of an arc reactor is discussed which is a multi-isotope radio-decay cell that can be created using low energy nuclear reactor technology which is a low-radiation fusion reactor.Here,palladium isotope is used as a core,and it generates a significant amount of power.It also introduces a new portable method to generate power without generating too much heat and heavy radiation.展开更多
基金This work was supported by the U.S.National Science Foundation(No.ECCS-1916068)the Army Research Office(No.W911NF-17-1-0428)the Air Force Office of Scientific Research(No.FA9550-18-1-0357).
文摘Terahertz(THz)wave generation from laser-induced air plasma generally requires a short temporal laser pulse.In contrast,it was observed that THz radiation from ionized liquid water prefers a longer pulse,wherein the mechanism remains unclear.We attribute the preference for longer pulse duration to the process of ionization and plasma formation in water,which is supported by a numerical simulation result showing that the highest electron density is achieved with a subpicosecond pulse.The explanation is further verified by the coincidence of our experimental result and simulation when the thickness of the water is varied.Other liquids are also tested to assure the preference for such a pulse is not exclusive to water.
基金supported by the National Natural Science Foundation of China(Grant Nos.11472036,11702026)
文摘Electromagnetic(EM) field is a consequence of the plasma generation induced by shock waves generated in impacts and explosions and is an important topic of study in aerospace and geophysics. Experimental research is frequently used to investigate the plasma generation in hypervelocity impacts and the EM wave emitted in chemical explosions. However, the basic plasma generation mechanism leading to the EM emission generated by the shock waves in chemical explosions is rarely studied.Therefore, a detailed investigation is performed to determine the state of the plasmas generated by the shock waves in air blast. In addition, a multi-component ionization model was improved to evaluate the ionization state of the generated plasmas. The proposed ionization model was combined with an AUSM+-up based finite volume method(FVM) to simulate the plasmas generated in the air blast. Two typical cases of simulation were carried out to investigate the relation between the shock waves and ionization, as well as the influence of ground reflection on the ionization state. It was found that the ionization zone was close behind the shock front in the air and propagates along with the shock waves. The interaction between the original shock waves and reflected shock waves was found to have a great impact of the order of 2–3 magnitudes, on the degree of ionization of the plasmas generated by the shock waves. This phenomenon explains the observation of additional EM pulses generated by ground reflection, as explored in the reference cited in this paper.
文摘Generation characteristics of vacuum discharge plasma are very important for the applied research of metal plasma. The vacuum discharge electrode configuration and the cathode material affect the generation characteristics of the metal plasma which consists of metal ions coming from cathode and generated by vacuum discharge. In this research, the generation characteristics of the metal plasma generated by vacuum discharge are discussed for four patterns of electrode configurations, i.e. cone-mesh electrode setup, cone-cross line electrode setup, cone-line electrode setup and cone-ring electrode setup. Characteristics of the metal plasma, such as elec- tron density, electron temperature, space potential, ion energy, are measured by the probe method for discussing the impacts of different electrode configurations on the density of generated metal plasma. Moreover, the diffusion velocities of the metal plasma are measured for cathode materials of Pb, Al, and Cu, respectively. The experimental results indicate that the plasma generated by the discharge of cone-ring electrode configuration possesses the maximum density and the metal plasma generated by the Al cathode possesses the fastest diffusion velocity and the highest kinetic energy.
基金This research was sponsored by the Army Research Office under Grant No.W911NF-17-1-0428Air Force Office of Scientific Research under Grant No.FA9550-18-1-0357National Science Foundation under Grant No.ECCS-1916068.
文摘Developing efficient and robust terahertz(THz)sources is of incessant interest in the THz community for their wide applications.With successive effort in past decades,numerous groups have achieved THz wave generation from solids,gases,and plasmas.However,liquid,especially liquid water has never been demonstrated as a THz source.One main reason leading the impediment is that water has strong absorption characteristics in the THz frequency regime.A thin water film under intense laser excitation was introduced as the THz source to mitigate the considerable loss of THz waves from the absorption.Laser-induced plasma formation associated with a ponderomotive forceinduced dipole model was proposed to explain the generation process.For the one-color excitation scheme,the water film generates a higher THz electric field than the air does under the identical experimental condition.Unlike the case of air,THz wave generation from liquid water prefers a sub-picosecond(200-800 fs)laser pulse rather than a femtosecond pulse(~50 fs).This observation results from the plasma generation process in water.For the two-color excitation scheme,the THz electric field is enhanced by one-order of magnitude in comparison with the one-color case.Meanwhile,coherent control of the THz field is achieved by adjusting the relative phase between the fundamental pulse and the second-harmonic pulse.To eliminate the total internal reflection of THz waves at the water-air interface of a water film,a water line produced by a syringe needle was used to emit THz waves.As expected,more THz radiation can be coupled out and detected.THz wave generation from other liquids were also tested.
文摘The results of an experimental investigation of the plasma dynamics in a magnetically insu- lated ion diode in bipolar-pulse mode are presented. The experiments were done at the pulsed TEMP-4M accelerator by formation of a first negative pulse (100 ns, 150-200 kV) and a second positive pulse (80 ns, 250-300 kV). The voltage-current diode characteristics were used to analyze the plasma behavior in the anode- cathode gap. It is shown that, during the first pulse, a discrete emissive surface is formed on the graphite potential electrode and a plasma forms by explosive-emission, which before the second pulse comes, fills the whole working surface of the electrode and spreads to the anode-cathode gap. An analytical expression is obtained for the total current in the cellular structure approximation. It is shown that the current build-up for a cathode surface with dis- crete emitting centers is described satisfac- torily by a modified Child-Langmuir formula wi- th a form factor decreasing from F = 6 to 1. It is found that, once plasma formation at the gra- phite potential electrode is complete and until the second positive pulse, the plasma speed is constant and equals 1.3 ±0.2 cm/μs.
文摘The design and the electric and emission characteristics of two handheld air plasma spray generators are presented. The plasma is generated by 60 Hz periodic discharges between two concentrically cylindrical electrodes. A ring magnet is used to rotate arc discharges, which sprays outward by an air flow. The rotation of arc discharges keeps the generated plasma in non-equilibrium state and at relatively low temperature (<55°C). The plasma effluent yet contains high energy electrons which dissociate molecular oxygen into atomic oxygen. The emission spectroscopy of the plasma plume reveals that the plasma effluent, which carries abundant atomic oxygen, extends from the cap of the plasma spray by about 25 to 30 mm. Tests on blood droplets and smeared blood samples revealed the effectiveness and mechanism of low temperature air plasma on clotting blood. Tests on oral pathogens show that air plasma creates a zone of microbial growth inhibition in each of six treated samples, including those of grampositive bacteria and fungi, and on a cultivating biofilm sample of Streptococcus mutans UA159. The medical applications of the air plasma sprays for 1) bleeding control, 2) wound healing, and 3) dental disinfection, are then illustrated and discussed. As animal models, pigs were used in the tests of stopping wound bleeding and post-operative observation of wound healing by this air plasma spray. The results show that the bleeding from a cut to an ear artery is stopped swiftly;this air plasma spray also shortens wound healing time to about half (from 14 days to 8 days) after stopping the bleeding of a cross cut wound in the ham area. In-vitro tests demonstrate that the plasma effluent of the spray can prevent the formation of dental biofilms and further eliminate the mature biofilms.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11774246 and 121774271)the National Key R&D Program of China(Grant No.2019YFC1711905)+2 种基金the Beijing Talents Project(Grant No.2018A19)the Sino-German Mobility Program of the Sino-German Center for Science Funding(Grant No.M-0225)the Capacity Building for Science&Technology Innovation-Fundamental Scientific Research Funds(Grant No.00820531120017).
文摘Interest of the research in terahertz(THz)wave has been strongly motivated by its wide applications in the fields of physics,chemistry,biology,and engineering.Developing efficient and reliable THz source is of uttermost priority in these researches.Numerous attempts have been made in fulfilling the THz generation.Greatly benefited from the progress of the ultrafast pulses,the laser-induced-plasma is one of the auspicious tools to provide desirable THz waves,owing to its superiorities in high power threshold,intense THz signal,and ultrawide THz spectrum.This paper reviews the physics and progress of the THz generation from the laser-induced plasmas,which are produced by gas,liquid,and solid.The characteristics of the emitted THz waves are also included.There are many complicated physical processes involved in the interactions of laser-plasma,making various laser-plasma scenarios in the THz generations.In view of this,we will only focus on the THz generation classified by physical mechanisms.Finally,we discuss a perspective on the future of THz generation from the laser-induced plasma,as well as its involved challenges.
文摘The resonant third-harmonic generation of a tion was investigated. Because of self-focusing self-focusing laser in plasma with a density transi- of the fundamental laser pulse, a transverse intensity gradient was created, which generated a plasma wave at the fundamental wave frequency. Phase matching was satisfied by using a Wiggler magnetic field, which provided additional angular too- mentum to the third-harmonic photon to make the process resonant. An enhancement was observed in the resonant third-harmonic generation of an intense short-pulse laser in plasma embedded with a magnetic Wiggler with a density transition. A plasma density ramp played an important role in the self-focusing, enhancing the third-harmonic generation in plasma. We also examined the ef- fect of the Wiggler magnetic field on the pulse slippage of the third-harmonic pulse in plasma. The pulse slippage was due to the group-velocity mismatch between the fundamental and third-harmonic pulses.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10335020 and 10425416, the National High-Tech ICF Committee in China, and the Knowledge Innovation Project of Chinese Academy of Sciences.
文摘Single attosecond pulses can be generated when an intense laser pulse focused in a volume of a few cubic wave- lengths （λ^3） is reflected from a solid plasma surface. With relativistic two-dimensional particle-in-cell simulations, we investigate the effects of the incident laser intensity and the target surface profiles on attosecond pulse generation. Usually the width of the reflected attosecond pulse decreases and its electromagnetic energy density increases with increasing laser intensity, while the energy conversion efficiency to the attoseond pulse decreases, By changing the target surface profile, such as using a convex surface or adding proper preplasma, one can further shorten the attosecond pulse duration and meanwhile increase its energy density.
基金Supported by the Key Development Program Foundation of Guangdong Province (No.2002C20809, 2004B50101001, 2005B50101001) Key Development Program Foundation of Guangxi Autonomy (No.0322012-8)
文摘The application and characteristics of relatively big volume plasma produced with cathodic glow discharges taking place across a gaseous envelope over the cathode which was dipped into electrolyte in hydrogen generation were studied. A critical investigation of the influence of methanol concentration and voltage across the circuit on the composition and power consumption per cubic meter of cathode liberating gas was carried out. The course of plasma under-liquid electrolysis has the typical characteristics of glow discharge electrolysis. The cathode liberating gas was in substantial excess of the Faraday law value. When the voltage across the circuit was equal to 550 V,the volume of cathodic gas with sodium carbonate solution was equal to 16.97 times the Faraday law value. The study showed that methanol molecules are more active than water molecules. The methanol molecules were decomposed at the plasma-catholyte interface by the radicals coming out the plasma mantle. Energy consumption per cubic meter of cathodic gases (WV) decreased while methanol concentration of the electrolytes increased. When methanol concentration equaled 5% (-),WV was 10.381×103 kJ/m3,less than the corresponding theoretic value of conventional water electrolysis method. The cathodic liberating gas was a mixture of hydrogen,carbon dioxide and carbon monoxide with over 95% hydrogen,if methanol concentration was more than 15% (-). The present research work revealed an innovative application of glow discharge and a new highly efficient hydrogen generation method,which depleted less resource and energy than normal electrolysis and is environmentally friendly.
基金the National Natural Science Foundation of China(Grant Nos.11135002,11075069,91026021,and 11075068)the Scholarship Award for Excellent Doctoral Student of Ministry of Education,China
文摘Spectral modulation and supercontinuum generation of a probe pulse is investigated by using the plasma grating induced by the interference of two infrared femtosecond laser pulses. The dependences of the supercontinuum generation from the probe pulse on the time delay, the relative polarization angle between the probe pulse and the two-pump pulses, and the input probe pulse energy are investigated. The far-field spatial profiles of the three pulses are measured with different time delays and relative polarization angle, and the core energy of the probe pulse as functions of the time delay and relative polarization angle are also shown.
基金supported by the Ministry of Science and Technology of the People’s Republic of China(Grant No.2018YFA0404803)Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB16010000)the National Natural Science Foundation of China(Grant Nos.11875307,11935008 and 11804348)。
文摘Spatiotemporal optical vortex(STOV)pulses carrying purely transverse intrinsic orbital angular momentum(TOAM)are attracting increasing attention because the TOAM provides a new degree of freedom to characterize light–matter interactions.In this paper,using particle-in-cell simulations,we present spatiotemporal high-harmonic generation in the relativistic region,driven by an intense STOV beam impinging on a plasma target.It is shown that the plasma surface acts as a spatial–temporal-coupled relativistic oscillating mirror with various frequencies.The spatiotemporal features are satisfactorily transferred to the harmonics such that the TOAM scales with the harmonic order.Benefitting from the ultrahigh damage threshold of the plasma over the optical media,the intensity of the harmonics can reach the relativistic region.This study provides a new approach for generating intense spatiotemporal extreme ultraviolet vortices and investigating STOV light–matter interactions at relativistic intensities.
文摘The purpose of this study is to explore the second harmonic generation(SHG)of a high power Cosh-Gaussian beam in cold collisionless plasma.The ponderomotive force causes carrier redistribution from high field to low field region in presence of a Cosh-Gaussian beam thereby producing density gradients in the transverse direction.The density gradients so produced the results in electron plasma wave(EPW)generation at the frequency of the input beam.The EPW interacts with the input beam resulting in the production of 2nd harmonics.WKB and paraxial approximations are employed for obtaining the 2nd order differential equation describing the behavior of the beam’s spot size against normalized distance.The impact of well-established laser-plasma parameters on the behavior of the beam’s spot size and SHG yield are also analyzed.The focusing behavior of the beam and SHG yield is enhanced with an increase in the density of plasma,the radius of the beam and the decentred parameter,and with a decrease in the intensity of the beam.The results of the current problem are really helpful for complete information of laser-plasma interaction physics.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11375265,11475259 and 11675264the National Basic Research Program of China under Grant No 2013CBA01504the Science Challenge Project under Grant No JCKY2016212A505
文摘The simple surface current model is extended to study the generation of high-order harmonics for a relativistic circularly polarized laser pulse interacting with a plasma grating surface. Both exact relativistic electron dynamics and optical interference of surface periodic structure are considered. It is found that high order harmonics in the specular direction are obviously suppressed whereas the harmonics of the grating periodicity are strongly enhanced and folded into small solid angles with respect to the surface direction. The conversion efficiency of certain harmonics is five orders of magnitude higher than that of the planar target cases. It provides an effective approach to generate a coherent radiation within the so-called ＇water window＇ while maintaining high conversion efficiency and narrow angle spread.
文摘Arc reactor is the design for a compact fusion reactor.In this paper,the mechanism of an arc reactor is discussed which is a multi-isotope radio-decay cell that can be created using low energy nuclear reactor technology which is a low-radiation fusion reactor.Here,palladium isotope is used as a core,and it generates a significant amount of power.It also introduces a new portable method to generate power without generating too much heat and heavy radiation.
