The matrix thermal properties have an important impact on laser-induced plasma,as the thermal effect dominates the interaction between ns-pulsed laser and matter,especially in metals.We used a series of pure metals an...The matrix thermal properties have an important impact on laser-induced plasma,as the thermal effect dominates the interaction between ns-pulsed laser and matter,especially in metals.We used a series of pure metals and aluminum alloys to measure plasma temperature and electron density through laser-induced breakdown spectroscopy,in order to investigate the effect of matrix thermal properties on laser-induced plasma.In pure metals,a significant negative linear correlation was observed between the matrix thermal storage coefficient and plasma temperature,while a weak correlation was observed with electron density.The results indicate that metals with low thermal conductivity or specific heat capacity require less laser energy for thermal diffusion or melting and evaporation,resulting in higher ablation rates and higher plasma temperatures.However,considering ionization energy,thermal effects may be a secondary factor affecting electron density.The experiment of aluminum alloy further confirms the influence of thermal conductivity on plasma temperature and its mechanism explanation.展开更多
Double-pulse LIBS is a promising technique for deep-sea applications.LIBS measurements in shallow water with up to 400 mJ each pulse were done to select laser parameters which promote optimized spectral line emission ...Double-pulse LIBS is a promising technique for deep-sea applications.LIBS measurements in shallow water with up to 400 mJ each pulse were done to select laser parameters which promote optimized spectral line emission from plasma even at elevated pressures,where line broadening until loss of most of the spectral information can occur.Optical emission spectroscopy,using a Czerny-Turner spectrometer,has been applied to investigate the dependence of the emitted radiation on laser parameters and hydrostatic pressure.It has been found,that higher laser pulse energies,especially with short pulse delay as required in high water pressure,can also have an adverse effect on the measured spectrum.展开更多
Time-integrated optical emission analysis of laser-induced plasma on Teflon is presented.Plasma was induced under atmospheric pressure air using transversely excited atmospheric CO_(2) laser pulses.Teflon is a C-based...Time-integrated optical emission analysis of laser-induced plasma on Teflon is presented.Plasma was induced under atmospheric pressure air using transversely excited atmospheric CO_(2) laser pulses.Teflon is a C-based polymer that is,among other things,interesting as a substrate for laser-induced breakdown spectroscopy analysis of liquid samples.This study aimed to determine the optimal experimental conditions for obtaining neutral and ionized C spectral lines and C2 and CN molecular band emission suitable for spectrochemical purposes.Evaluation of plasma parameters was done using several spectroscopic techniques.Stark profiles of appropriate C ionic lines were used to determine electron number density.The ratio of the integral intensity of ionic-to-atomic C spectral lines was used to determine the ionization temperature.A spectral emission of C2 Swan and CN violet bands system was used to determine the temperature of the colder,peripheral parts of plasma.We critically analyzed the use of molecular emission bands as a tool for plasma diagnostics and suggested methods for possible improvements.展开更多
Plasma is a significant medium in high-energy density physics since it can hardly be damaged. For some applications such as plasma based backward Raman amplification （BRA）, uniform high-density and large-scale plasm...Plasma is a significant medium in high-energy density physics since it can hardly be damaged. For some applications such as plasma based backward Raman amplification （BRA）, uniform high-density and large-scale plasma channels are required. In the previous experiment, the plasma transverse diameter and density are 50-200 μm and 1-2 x 10^19 cm-3, here we enhance them to 0.8 mm and 8 x 10^19 cm-3, respectively. Moreover, the gradient plasma is investigated in our experiment. A proper plasma gradient can be obtained with suitable pulse energy and delay. The experimental results are useful for plasma physics and nonlinear optics.展开更多
The interaction of laser-induced plasma and bow shock over a blunt body is inves- tigated numerically in an M∞ =6.5 supersonic flow. A ray-tracing method is used for simulating the process of laser focusing. The gas ...The interaction of laser-induced plasma and bow shock over a blunt body is inves- tigated numerically in an M∞ =6.5 supersonic flow. A ray-tracing method is used for simulating the process of laser focusing. The gas located at the focused zone is ionized and broken down and transformed into plasma. In a supersonic flow the plasma moves downstream and begins to interact with the bow shock when it approaches the surface of the blunt body. The parameters of flowfield and blunt body surface are changed due to the interaction. By analyzing phenomena occurring in the complex unsteady flowfield during the interaction in detail, we can better under- stand the change of pressure on the blunt body surface and the mechanism of drag reduction by laser energy deposition. The results show that the bow shock is changed into an oblique shock due to the interaction of the laser-induced low-density zone with the bow shock, so the wave drag of the blunt body is reduced.展开更多
The velocity of critical surface at microwave band in laser-induced plasma was measured and the results are presented. The results indicate that the velocity of critical surface with low electron density is larger tha...The velocity of critical surface at microwave band in laser-induced plasma was measured and the results are presented. The results indicate that the velocity of critical surface with low electron density is larger than that with the high one; and the velocity of critical surface increases with the laser power density.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
Particles can be removed from a silicon surface by means of irradiation and a laser plasma shock wave.The particles and silicon are heated by the irradiation and they will expand differently due to their different exp...Particles can be removed from a silicon surface by means of irradiation and a laser plasma shock wave.The particles and silicon are heated by the irradiation and they will expand differently due to their different expansion coefficients,making the particles easier to be removed.Laser plasma can ionize and even vaporize particles more significantly than an incident laser and,therefore,it can remove the particles more efficiently.The laser plasma shock wave plays a dominant role in removing particles,which is attributed to its strong burst force.The pressure of the laser plasma shock wave is determined by the laser pulse energy and the gap between the focus of laser and substrate surface.In order to obtain the working conditions for particle removal,the removal mechanism,as well as the temporal and spatial characteristics of velocity,propagation distance and pressure of shock wave have been researched.On the basis of our results,the conditions for nano-particle removal are achieved.展开更多
The optimal spectral excitation and acquisition scheme is explored by studying the effect of the lensto-sample distance(LTSD)on the spatial homogeneity and emission spectra of flat-top laser converging spot induced pl...The optimal spectral excitation and acquisition scheme is explored by studying the effect of the lensto-sample distance(LTSD)on the spatial homogeneity and emission spectra of flat-top laser converging spot induced plasma.The energy distribution characteristics before and after the convergence of the laser beam with quasi flat-top intensity profile used in this study are theoretically simulated and experimentally measured.For an aspheric converging mirror with a focal length of100 mm,the LTSD(106 mm≥LTSD≥96 mm)was changed by raising the stainless-steel sample height.The plasma images acquired by ICCD show that there is air breakdown when the sample is below the focal point,and a ring-like plasma is produced when the sample is above the focal point.When the sample is located near the focal point,the plasma shape resembles a hemisphere.Since the spectral acquisition region is confined to the plasma core and the image contains all the optical information of the plasma,it has a lower relative standard deviation(RSD)than the spectral lines.When the sample surface is slightly higher than the focal plane of the lens,the converging spot has a quasi flat-top distribution,the spatial distribution of the plasma is more uniform,and the spectral signal is more stable.Simultaneously,there is little difference between the RSD of the plasma image and the laser energy.In order to further improve the stability of the spectral signal,it is necessary to expand the spectral acquisition area.展开更多
Laser-induced plasma is often produced in the presence of background gas,which causes some new physical processes.In this work,a two-dimensional axisymmetric radiation fluid dynamics model is used to numerically simul...Laser-induced plasma is often produced in the presence of background gas,which causes some new physical processes.In this work,a two-dimensional axisymmetric radiation fluid dynamics model is used to numerically simulate the expansion process of plasma under different pressures and gases,in which the multiple interaction processes of diffusion,viscosity and heat conduction between the laser ablated target vapor and the background gas are further considered,and the spatio-temporal evolutions of plasma parameters(species number density,expansion velocity,size and electron temperature)as well as the emission spectra are obtained.The consistency between the actual and simulated spectra of aluminum plasma in 1 atm argon verifies the correctness of the model and the numerical simulation,thus providing a refinement analysis method for the basic research of plasma expansion in gases and the application of laser-induced breakdown spectroscopy.展开更多
A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal...A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal evolution of 2-dimensional transverse profile of ultrafast electron bunches repelled by the formed transient electric field of laser-induced plasma on a silver needle is investigated, and the pulse-width can be obtained by analyzing these time-dependent images.This approach can characterize radio-frequency compressed ultrafast electron bunches with picosecond or sub-picosecond timescale and up to 105 electron numbers.展开更多
A combination of spark discharge and nanoparticle-enhanced laser-induced plasma spectroscopy is investigated.Depositing Au nanoparticles at the surface of a brass target can enhance the coupling of the target and the ...A combination of spark discharge and nanoparticle-enhanced laser-induced plasma spectroscopy is investigated.Depositing Au nanoparticles at the surface of a brass target can enhance the coupling of the target and the laser.More atoms in the brass sample are excited.As a secondary excitation source,spark discharge reheats the generated plasma,which further amplifies the enhancement results of nanoparticles.The spectral intensity with the spark discharge increases more obviously with nanoparticle concentration increasing than without the spark discharge.Also,plasma temperature and electron density are calculated by the Boltzmann plot and Stark broadening.The changes in the plasma temperature and electron density are consistent with the spectral emission changes.展开更多
An experiment of femtosecond laser-induced breakdown in argon with a pressure below normal atmospheric pressure is performed. The breakdown spectrum is mainly due to the electronic relaxation of excited Ar atoms and A...An experiment of femtosecond laser-induced breakdown in argon with a pressure below normal atmospheric pressure is performed. The breakdown spectrum is mainly due to the electronic relaxation of excited Ar atoms and Ar ions. The lifetimes and characteristics of the Ar plasma are extensively studied by the time-integrated and time-resolved optical emission spectroscopy technique, which is also discussed. Under the assumption of local thermodynamic equilibrium （LTE）, the plasma temperature is calculated. Moreover, the electron density is accessed from the Stark broadening of the ionized argon lines. Finally, the validity of applications of LTE is also discussed.展开更多
We report spectroscopic studies on plasma electron number density of laser-induced plasma produced by ns-Nd：YAG laser light pulses on an aluminum sample in air at atmospheric pressure. The effect of different laser e...We report spectroscopic studies on plasma electron number density of laser-induced plasma produced by ns-Nd：YAG laser light pulses on an aluminum sample in air at atmospheric pressure. The effect of different laser energy and the effect of different laser wavelengths were compared. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadened as well as using the Saha-Boltzmann equation （SBE）. Each approach was also carried out by using the AI emission line and Mg emission lines. It was observed that the,SBE method generated a little higher electron number density value than the Stark broadening, method, but within the experimental uncertainty range. Comparisons of Ne determined by the two methods show the presence of a linear relation which is independent of laser energy or laser wavelength. These results show the applicability of the SBE method for Are determination, especially when the system does not have any pure emission lines whose electron impact factor is known, Also use of Mg lines gives superior results than Al lines.展开更多
Laser-Induced Breakdown Spectroscopy （LIBS） has been demonstrated to be an effective method for slag analysis. In order to better clarify the nature of the plasma generated from a slag sample, an Nd：YAG pulse laser...Laser-Induced Breakdown Spectroscopy （LIBS） has been demonstrated to be an effective method for slag analysis. In order to better clarify the nature of the plasma generated from a slag sample, an Nd：YAG pulse laser at 1064 nm wavelength was used to ablate the slag sample in air. The temporal and spatial evolutions of plasma parameters, including emission intensity, electronic density and plasma temperature, have been studied. It is shown that the electron density and plasma temperature drop off rapidly with the delay time as a result of plasma expansion and cooling. It has been found that the electron density of the whole plasma is close to that of the center regions in the plasma. The results of the spatial distributions on the two-dimensional plane have shown that there is a big region with lower electron density values caused by the recombination process in the center of the plasma. The maximum of the plasma temperature takes place at the regions close to the target, and the border of the plasma front-head has higher plasma temperatures than that of the center part.展开更多
The effect of the matrix temperature on laser-induced plasma generated in bulk water by using a532 nm pulsed laser beam has been studied.Ca Ⅰ and Ⅱ emission line intensities were recorded for an aqueous solution of ...The effect of the matrix temperature on laser-induced plasma generated in bulk water by using a532 nm pulsed laser beam has been studied.Ca Ⅰ and Ⅱ emission line intensities were recorded for an aqueous solution of CaCl2 in the temperature range of 7℃-70℃.The emission line intensities did not follow the matrix temperature in our experiments.Maximum intensities were observed at ~18℃ for both lines.Herein,a possible mechanism responsible for the observed variation in intensity is suggested,in which laser-produced bubbles play important roles.Bubble formation is essential to ignite plasma in the liquid and more feasible at the higher liquid temperature.However,the abundant bubbles at the higher temperature can scatter the incident laser beam more effectively to decrease the energy delivered for the laser-induced plasma.Thus,these two roles have effects on the optical emission intensities in opposite ways.The validity of the suggested mechanism is discussed based on the plasma temperature,temperature dependence of the refractive index of water,plasma electron density,scattered light intensity,and plasma ignition threshold energy.Our result indicates that the temperature of the liquid is also an important parameter to be considered in the laser-induced breakdown spectroscopy analysis of bulk liquid samples and its application in deep-sea exploration.展开更多
The temporal evolution of stark-broadening of H_(β) line in laser-induced plasma in methane is investigated and the electronic density is determined from the Stark-broadened linewidth of the Balmer beta line.The maxi...The temporal evolution of stark-broadening of H_(β) line in laser-induced plasma in methane is investigated and the electronic density is determined from the Stark-broadened linewidth of the Balmer beta line.The maximum half-width of the line is more than 100Å and the deduced electronic density is about 4x10^(17)cm^(-3).展开更多
The plasma shielding effect is one of the major weaknesses of laser-induced breakdown spectroscopy(LIBS)as it causes non-linearity in signal strength.Although LIBS is typically carried out in constant laser energy,thi...The plasma shielding effect is one of the major weaknesses of laser-induced breakdown spectroscopy(LIBS)as it causes non-linearity in signal strength.Although LIBS is typically carried out in constant laser energy,this non-linearity causes a reduction in sensitivity.In this work,we systematically examine laser-induced plasma,formed by two different excitation source modes,i.e.single pulse(SP)-excitation and single-beam-splitting double-pulse(SBS-DP)-excitation over Zr-2.5%Nb alloy.The two most important plasma parameters influencing the emission line intensity,plasma temperature(Te)and electron density(Ne)were studied and compared for both modes of laser excitation.Comparison of the results conclusively demonstrates that due to the splitting of the laser energy in the SBS-DP mode,the plasma shielding effect is significantly reduced.The reduced plasma shielding translates to an increased laser–sample coupling under SBS-DP mode.Temporal imaging of the total intensity of the laser-induced plasma in both excitation modes was also studied.The study shows how the plasma shielding effect can be reduced to improve the analytical quality of the LIBS methodology.展开更多
The spectral characteristic of laser-induced plasma in soil was studied in this work,laser-induced breakdown spectroscopy was used to analyze the spectral characteristic of plasma under the condition of different time...The spectral characteristic of laser-induced plasma in soil was studied in this work,laser-induced breakdown spectroscopy was used to analyze the spectral characteristic of plasma under the condition of different time delays and irradianccs.Moreover,the time evolution characteristics of plasma temperature and electron density were discussed.Within the time delay range of 0-5μs,the spectral intensity of the characteristic lines of Si I:288.158 nm,Ti I:336.126 nm.Al I:394.400 nm and Fe I:438.354 nm of the four main elements in two kinds of national standard soil decayed exponentially with time.The average lifetime of the spectral lines was nearly 1.56μs.Under the condition of different time delays,the spectral intensity of Pb I:405.78 nm in soil increased linearly with laser energy.However,the slope between the spectral intensity and laser energy decreased exponentially with the increase in time delay,from 4.91 to 0.99 during 0-5μs.The plasma temperature was calculated by the Boltzmann plot method and the electron density was obtained by inversion of the full width at half maximum of the spectrum.The plasma temperature decreased from 8900 K to 7800 K and the electron density decreased from 1.5 x 1Ol7cm-3 to 7.8 x lO16cm-3 in the range of 0-5μs.展开更多
In this Letter,we employ fused silica and two types of optical glass as examples to investigate the coherent terahertz(THz)wave emission from laser-ionized isotropic transparent dielectrics.Based on the laser energy a...In this Letter,we employ fused silica and two types of optical glass as examples to investigate the coherent terahertz(THz)wave emission from laser-ionized isotropic transparent dielectrics.Based on the laser energy and incident angle dependences,we ascribe the THz emission to the ponderomotive force-induced dipole oscillation.Additionally,our investigation on the dependence of THz amplitude on the laser pulse duration confirms the dominant role of avalanche ionization in solid dielectrics.The THz emission can be utilized to indirectly monitor the ultrafast dynamics of carrier generation and motion during the laser ionization process of solid dielectrics.展开更多
基金supported by the National Key Research and Development Project(Grant No.2018YFC2001100).
文摘The matrix thermal properties have an important impact on laser-induced plasma,as the thermal effect dominates the interaction between ns-pulsed laser and matter,especially in metals.We used a series of pure metals and aluminum alloys to measure plasma temperature and electron density through laser-induced breakdown spectroscopy,in order to investigate the effect of matrix thermal properties on laser-induced plasma.In pure metals,a significant negative linear correlation was observed between the matrix thermal storage coefficient and plasma temperature,while a weak correlation was observed with electron density.The results indicate that metals with low thermal conductivity or specific heat capacity require less laser energy for thermal diffusion or melting and evaporation,resulting in higher ablation rates and higher plasma temperatures.However,considering ionization energy,thermal effects may be a secondary factor affecting electron density.The experiment of aluminum alloy further confirms the influence of thermal conductivity on plasma temperature and its mechanism explanation.
基金funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)–Project No.454848899。
文摘Double-pulse LIBS is a promising technique for deep-sea applications.LIBS measurements in shallow water with up to 400 mJ each pulse were done to select laser parameters which promote optimized spectral line emission from plasma even at elevated pressures,where line broadening until loss of most of the spectral information can occur.Optical emission spectroscopy,using a Czerny-Turner spectrometer,has been applied to investigate the dependence of the emitted radiation on laser parameters and hydrostatic pressure.It has been found,that higher laser pulse energies,especially with short pulse delay as required in high water pressure,can also have an adverse effect on the measured spectrum.
基金funded by the Ministry of Education,Science and Technological Development of the Republic of Serbia(Nos.451-03-68/2022-14/200017 and 451-03-68/2022-14/200146)the financial support of the State Committee on Science and Technology of the Republic of Belarusthe Belarusian Republican Foundation for Fundamental Research(No.F20SRBG-001)。
文摘Time-integrated optical emission analysis of laser-induced plasma on Teflon is presented.Plasma was induced under atmospheric pressure air using transversely excited atmospheric CO_(2) laser pulses.Teflon is a C-based polymer that is,among other things,interesting as a substrate for laser-induced breakdown spectroscopy analysis of liquid samples.This study aimed to determine the optimal experimental conditions for obtaining neutral and ionized C spectral lines and C2 and CN molecular band emission suitable for spectrochemical purposes.Evaluation of plasma parameters was done using several spectroscopic techniques.Stark profiles of appropriate C ionic lines were used to determine electron number density.The ratio of the integral intensity of ionic-to-atomic C spectral lines was used to determine the ionization temperature.A spectral emission of C2 Swan and CN violet bands system was used to determine the temperature of the colder,peripheral parts of plasma.We critically analyzed the use of molecular emission bands as a tool for plasma diagnostics and suggested methods for possible improvements.
基金Project supported by the Development Foundation of the Chinese Academy of Engineering Physics(Grant Nos.2012A0401019 and 2013A0401019)
文摘Plasma is a significant medium in high-energy density physics since it can hardly be damaged. For some applications such as plasma based backward Raman amplification （BRA）, uniform high-density and large-scale plasma channels are required. In the previous experiment, the plasma transverse diameter and density are 50-200 μm and 1-2 x 10^19 cm-3, here we enhance them to 0.8 mm and 8 x 10^19 cm-3, respectively. Moreover, the gradient plasma is investigated in our experiment. A proper plasma gradient can be obtained with suitable pulse energy and delay. The experimental results are useful for plasma physics and nonlinear optics.
基金supported by National Natural Science Foundation of China(No.90916015)
文摘The interaction of laser-induced plasma and bow shock over a blunt body is inves- tigated numerically in an M∞ =6.5 supersonic flow. A ray-tracing method is used for simulating the process of laser focusing. The gas located at the focused zone is ionized and broken down and transformed into plasma. In a supersonic flow the plasma moves downstream and begins to interact with the bow shock when it approaches the surface of the blunt body. The parameters of flowfield and blunt body surface are changed due to the interaction. By analyzing phenomena occurring in the complex unsteady flowfield during the interaction in detail, we can better under- stand the change of pressure on the blunt body surface and the mechanism of drag reduction by laser energy deposition. The results show that the bow shock is changed into an oblique shock due to the interaction of the laser-induced low-density zone with the bow shock, so the wave drag of the blunt body is reduced.
文摘The velocity of critical surface at microwave band in laser-induced plasma was measured and the results are presented. The results indicate that the velocity of critical surface with low electron density is larger than that with the high one; and the velocity of critical surface increases with the laser power density.
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.
基金Project supported by the National Natural Science Foundation of China(Grant No.11574221)
文摘Particles can be removed from a silicon surface by means of irradiation and a laser plasma shock wave.The particles and silicon are heated by the irradiation and they will expand differently due to their different expansion coefficients,making the particles easier to be removed.Laser plasma can ionize and even vaporize particles more significantly than an incident laser and,therefore,it can remove the particles more efficiently.The laser plasma shock wave plays a dominant role in removing particles,which is attributed to its strong burst force.The pressure of the laser plasma shock wave is determined by the laser pulse energy and the gap between the focus of laser and substrate surface.In order to obtain the working conditions for particle removal,the removal mechanism,as well as the temporal and spatial characteristics of velocity,propagation distance and pressure of shock wave have been researched.On the basis of our results,the conditions for nano-particle removal are achieved.
基金supported by the Young Scientists Fund of National Natural Science Foundation of China(No.12004388)the National High Technology Research and Development Program of China(No.2021YFB3202402)+1 种基金the Key Research and Development Plan of Anhui Province(No.202104i07020009)the Collaborative Innovation Program of Hefei Science Center,CAS(No.2021HSCCIP005)。
文摘The optimal spectral excitation and acquisition scheme is explored by studying the effect of the lensto-sample distance(LTSD)on the spatial homogeneity and emission spectra of flat-top laser converging spot induced plasma.The energy distribution characteristics before and after the convergence of the laser beam with quasi flat-top intensity profile used in this study are theoretically simulated and experimentally measured.For an aspheric converging mirror with a focal length of100 mm,the LTSD(106 mm≥LTSD≥96 mm)was changed by raising the stainless-steel sample height.The plasma images acquired by ICCD show that there is air breakdown when the sample is below the focal point,and a ring-like plasma is produced when the sample is above the focal point.When the sample is located near the focal point,the plasma shape resembles a hemisphere.Since the spectral acquisition region is confined to the plasma core and the image contains all the optical information of the plasma,it has a lower relative standard deviation(RSD)than the spectral lines.When the sample surface is slightly higher than the focal plane of the lens,the converging spot has a quasi flat-top distribution,the spatial distribution of the plasma is more uniform,and the spectral signal is more stable.Simultaneously,there is little difference between the RSD of the plasma image and the laser energy.In order to further improve the stability of the spectral signal,it is necessary to expand the spectral acquisition area.
基金supported by National Key R&D Program of China(No.2017YFA0304203)National Energy R&D Center of Petroleum Refining Technology(RIPP,SINOPEC)+4 种基金Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China(No.IRT_17R70)National Natural Science Foundation of China(NSFC)(Nos.61975103,61875108,61775125,11434007)Major Special Science and Technology Projects in Shanxi(No.201804D131036)111 project(No.D18001)Fund for Shanxi‘1331KSC’。
文摘Laser-induced plasma is often produced in the presence of background gas,which causes some new physical processes.In this work,a two-dimensional axisymmetric radiation fluid dynamics model is used to numerically simulate the expansion process of plasma under different pressures and gases,in which the multiple interaction processes of diffusion,viscosity and heat conduction between the laser ablated target vapor and the background gas are further considered,and the spatio-temporal evolutions of plasma parameters(species number density,expansion velocity,size and electron temperature)as well as the emission spectra are obtained.The consistency between the actual and simulated spectra of aluminum plasma in 1 atm argon verifies the correctness of the model and the numerical simulation,thus providing a refinement analysis method for the basic research of plasma expansion in gases and the application of laser-induced breakdown spectroscopy.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11004060,11027403,and 11304224)the Shanghai Municipal Science and Technology Commission,China(Grant Nos.10XD1401800,09142200501,09ZR1409300,09JC1404700,and 10JC1404500)
文摘A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal evolution of 2-dimensional transverse profile of ultrafast electron bunches repelled by the formed transient electric field of laser-induced plasma on a silver needle is investigated, and the pulse-width can be obtained by analyzing these time-dependent images.This approach can characterize radio-frequency compressed ultrafast electron bunches with picosecond or sub-picosecond timescale and up to 105 electron numbers.
基金Project supported by the National Key Research and Development Program of China(Grant No.2019YFA0307701)the National Natural Science Foundation of China(Grant Nos.11674128,11674124,and 11974138)the Jilin Provincial Scientific and Technological Development Program,China(Grant No.20170101063JC)。
文摘A combination of spark discharge and nanoparticle-enhanced laser-induced plasma spectroscopy is investigated.Depositing Au nanoparticles at the surface of a brass target can enhance the coupling of the target and the laser.More atoms in the brass sample are excited.As a secondary excitation source,spark discharge reheats the generated plasma,which further amplifies the enhancement results of nanoparticles.The spectral intensity with the spark discharge increases more obviously with nanoparticle concentration increasing than without the spark discharge.Also,plasma temperature and electron density are calculated by the Boltzmann plot and Stark broadening.The changes in the plasma temperature and electron density are consistent with the spectral emission changes.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11135002,11075069,91026021,11075068and 10975065the Scholarship Award for Excellent Doctoral Student by the Ministry of Education of China
文摘An experiment of femtosecond laser-induced breakdown in argon with a pressure below normal atmospheric pressure is performed. The breakdown spectrum is mainly due to the electronic relaxation of excited Ar atoms and Ar ions. The lifetimes and characteristics of the Ar plasma are extensively studied by the time-integrated and time-resolved optical emission spectroscopy technique, which is also discussed. Under the assumption of local thermodynamic equilibrium （LTE）, the plasma temperature is calculated. Moreover, the electron density is accessed from the Stark broadening of the ionized argon lines. Finally, the validity of applications of LTE is also discussed.
文摘We report spectroscopic studies on plasma electron number density of laser-induced plasma produced by ns-Nd：YAG laser light pulses on an aluminum sample in air at atmospheric pressure. The effect of different laser energy and the effect of different laser wavelengths were compared. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadened as well as using the Saha-Boltzmann equation （SBE）. Each approach was also carried out by using the AI emission line and Mg emission lines. It was observed that the,SBE method generated a little higher electron number density value than the Stark broadening, method, but within the experimental uncertainty range. Comparisons of Ne determined by the two methods show the presence of a linear relation which is independent of laser energy or laser wavelength. These results show the applicability of the SBE method for Are determination, especially when the system does not have any pure emission lines whose electron impact factor is known, Also use of Mg lines gives superior results than Al lines.
基金supported by National Natural Science Foundation of China(No.11075184)the Knowledge Innovation Program of the Chinese Academy of Sciences(No.Y03RC21124)
文摘Laser-Induced Breakdown Spectroscopy （LIBS） has been demonstrated to be an effective method for slag analysis. In order to better clarify the nature of the plasma generated from a slag sample, an Nd：YAG pulse laser at 1064 nm wavelength was used to ablate the slag sample in air. The temporal and spatial evolutions of plasma parameters, including emission intensity, electronic density and plasma temperature, have been studied. It is shown that the electron density and plasma temperature drop off rapidly with the delay time as a result of plasma expansion and cooling. It has been found that the electron density of the whole plasma is close to that of the center regions in the plasma. The results of the spatial distributions on the two-dimensional plane have shown that there is a big region with lower electron density values caused by the recombination process in the center of the plasma. The maximum of the plasma temperature takes place at the regions close to the target, and the border of the plasma front-head has higher plasma temperatures than that of the center part.
基金supported by the Korea Basic Science Institute(KBSI)National Research Facilities&Equipment Center(NFEC)grant funded by the Korean government(Ministry of Education)(No.2019R1A6C1010005)。
文摘The effect of the matrix temperature on laser-induced plasma generated in bulk water by using a532 nm pulsed laser beam has been studied.Ca Ⅰ and Ⅱ emission line intensities were recorded for an aqueous solution of CaCl2 in the temperature range of 7℃-70℃.The emission line intensities did not follow the matrix temperature in our experiments.Maximum intensities were observed at ~18℃ for both lines.Herein,a possible mechanism responsible for the observed variation in intensity is suggested,in which laser-produced bubbles play important roles.Bubble formation is essential to ignite plasma in the liquid and more feasible at the higher liquid temperature.However,the abundant bubbles at the higher temperature can scatter the incident laser beam more effectively to decrease the energy delivered for the laser-induced plasma.Thus,these two roles have effects on the optical emission intensities in opposite ways.The validity of the suggested mechanism is discussed based on the plasma temperature,temperature dependence of the refractive index of water,plasma electron density,scattered light intensity,and plasma ignition threshold energy.Our result indicates that the temperature of the liquid is also an important parameter to be considered in the laser-induced breakdown spectroscopy analysis of bulk liquid samples and its application in deep-sea exploration.
文摘The temporal evolution of stark-broadening of H_(β) line in laser-induced plasma in methane is investigated and the electronic density is determined from the Stark-broadened linewidth of the Balmer beta line.The maximum half-width of the line is more than 100Å and the deduced electronic density is about 4x10^(17)cm^(-3).
文摘The plasma shielding effect is one of the major weaknesses of laser-induced breakdown spectroscopy(LIBS)as it causes non-linearity in signal strength.Although LIBS is typically carried out in constant laser energy,this non-linearity causes a reduction in sensitivity.In this work,we systematically examine laser-induced plasma,formed by two different excitation source modes,i.e.single pulse(SP)-excitation and single-beam-splitting double-pulse(SBS-DP)-excitation over Zr-2.5%Nb alloy.The two most important plasma parameters influencing the emission line intensity,plasma temperature(Te)and electron density(Ne)were studied and compared for both modes of laser excitation.Comparison of the results conclusively demonstrates that due to the splitting of the laser energy in the SBS-DP mode,the plasma shielding effect is significantly reduced.The reduced plasma shielding translates to an increased laser–sample coupling under SBS-DP mode.Temporal imaging of the total intensity of the laser-induced plasma in both excitation modes was also studied.The study shows how the plasma shielding effect can be reduced to improve the analytical quality of the LIBS methodology.
文摘The spectral characteristic of laser-induced plasma in soil was studied in this work,laser-induced breakdown spectroscopy was used to analyze the spectral characteristic of plasma under the condition of different time delays and irradianccs.Moreover,the time evolution characteristics of plasma temperature and electron density were discussed.Within the time delay range of 0-5μs,the spectral intensity of the characteristic lines of Si I:288.158 nm,Ti I:336.126 nm.Al I:394.400 nm and Fe I:438.354 nm of the four main elements in two kinds of national standard soil decayed exponentially with time.The average lifetime of the spectral lines was nearly 1.56μs.Under the condition of different time delays,the spectral intensity of Pb I:405.78 nm in soil increased linearly with laser energy.However,the slope between the spectral intensity and laser energy decreased exponentially with the increase in time delay,from 4.91 to 0.99 during 0-5μs.The plasma temperature was calculated by the Boltzmann plot method and the electron density was obtained by inversion of the full width at half maximum of the spectrum.The plasma temperature decreased from 8900 K to 7800 K and the electron density decreased from 1.5 x 1Ol7cm-3 to 7.8 x lO16cm-3 in the range of 0-5μs.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.62075157,62375199,and 62235013)the Tianjin Municipal Fund for Distinguished Young Scholars(No.20JCJQJC00190)the Key Fund of Shenzhen Natural Science Foundation(No.JCYJ20200109150212515)。
文摘In this Letter,we employ fused silica and two types of optical glass as examples to investigate the coherent terahertz(THz)wave emission from laser-ionized isotropic transparent dielectrics.Based on the laser energy and incident angle dependences,we ascribe the THz emission to the ponderomotive force-induced dipole oscillation.Additionally,our investigation on the dependence of THz amplitude on the laser pulse duration confirms the dominant role of avalanche ionization in solid dielectrics.The THz emission can be utilized to indirectly monitor the ultrafast dynamics of carrier generation and motion during the laser ionization process of solid dielectrics.
