In indirect-driven laser fusion experiments,the movement of the laser absorption layer will distort the radiation uniformity on the capsule.The gold foam has advantages in symmetry control and lowering wall plasma blo...In indirect-driven laser fusion experiments,the movement of the laser absorption layer will distort the radiation uniformity on the capsule.The gold foam has advantages in symmetry control and lowering wall plasma blowoff when used in an inertial confinement fusion(ICF)hohlraum.This work investigates the motion of the laser absorption cutoff position using lowdensity foam gold walls.It is found that the motion of the laser absorption cutoff position can be significantly mitigated through optimal initial low density,tailored to a specific laser shape.For a short square laser pulse,the laser absorption cutoff position remains almost stationary at an initial density of approximately 0.6 g cm^(-3).For a long-shaped laser pulse,the minimal motion of the laser absorption cutoff position is observed at an initial density of about 0.1 g cm^(-3).This approach allows for the adjustment of the symmetry of the hohlraum radiation source.The insights gained from this study serve as a crucial reference for optimizing the hohlraum wall density.展开更多
The measurement of the combustion characteristics of a single biomass particle is essential for studying massive biofuel energy conversion process;however,it is challenging due to the small physical scale of the bioma...The measurement of the combustion characteristics of a single biomass particle is essential for studying massive biofuel energy conversion process;however,it is challenging due to the small physical scale of the biomass particle flame.In this work,we report an investigation of the combustion behavior of single lignin and single cellulose particle through CO_(2)absorption spectroscopy and high-speed photography.The biomass samples are prepared with an initial diameter of about 1.0 mm and are ignited on a heating plate placed inside a multi-pass absorption cell.The shape and size transformation of single biomass particle are recorded through high-speed photography,and the combustion temperature and CO_(2)column densities are measured through laser absorption spectroscopy at 4.172µm.We find that the maximum combustion temperatures are 1662±38 K and 1569±26 K for lignin and cellulose particle,respectively.Besides,we find that CO_(2)generation precedes the generation of visible volatile flame for cellulose particle.While for lignin particle,the CO_(2)generation is found to be almost at the same time as its volatile combustion stage begins.The measurement technique and results presented in this work are of practical interest for biomass combustion studies and arc meaningful for the development of biomass thermal conversion mode.展开更多
Exhaust gas temperature is an important factor in NOx, THC and PM emissions of engines. Especially 2D temperature and concentration distribution plays an important role for the engine efficiency. A thermocouple is int...Exhaust gas temperature is an important factor in NOx, THC and PM emissions of engines. Especially 2D temperature and concentration distribution plays an important role for the engine efficiency. A thermocouple is intrinsically a point temperature measurement method and noncontact 2D temperature distribution cannot be attained by thermocouples. Recently, as a measurement technique with high sensitivity and high response, laser diagnostics has been developed and applied to the actual engine combustions. With these engineering developments, transient phenomena such as start-ups and load changes in engines have been gradually elucidated in various conditions. In this study, the theoretical and experimental research has been conducted in order to develop the noncontact and fast response 2D temperature and concentration distribution measurement method. The method is based on a Computed Tomography （CT） method using absorption spectra of water vapor at 1388 nm. It has been demonstrated that the method has been successfully applied to engine exhausts to measure 2D temperature distributions.展开更多
In this paper, the compositions in a laser absorption region can be determined from the experiment of laser impulse coupling. When the ambient pressure varies from 9325 to 33325Pa, the compositions are vapour and plas...In this paper, the compositions in a laser absorption region can be determined from the experiment of laser impulse coupling. When the ambient pressure varies from 9325 to 33325Pa, the compositions are vapour and plasma; while from 35325 to 101325Pa, they are ambient air and plasma. By analysing the relation between the degree of compression and the ambient pressure, the compositions can be determined and the variation of plasma can be explained.展开更多
Densities of Ar metastable states 1s5 and 1s3 are measured by using the tunable diode laser absorption spectroscopy（TDLAS） in Ar and Ar/O2 mixture dual-frequency capacitively coupled plasma（DF-CCP）. We investigate...Densities of Ar metastable states 1s5 and 1s3 are measured by using the tunable diode laser absorption spectroscopy（TDLAS） in Ar and Ar/O2 mixture dual-frequency capacitively coupled plasma（DF-CCP）. We investigate the effects of high-frequency（HF, 60 MHz） power, low-frequency（LF, 2 MHz） power, and working pressure on the density of Ar metastable states for three different gas components（0%, 5%, and 10% oxygen mixed in argon）. The dependence of Ar metastable state density on the oxygen content is also studied at different working pressures. It is found that densities of Ar metastable states in discharges with different gas components exhibit different behaviors as HF power increases. With the increase of HF power, the metastable density increases rapidly at the initial stage, and then tends to be saturated at a higher HF power. With a small fraction（5% or 10%） of oxygen added in argon plasma, a similar change of the Ar metastable density with HF power can be observed, but the metastable density is saturated at a higher HF power than in the pure argon discharge. In the DF-CCP, the metastable density is found to be higher than in a single frequency discharge, and has weak dependence on LF power. As working pressure increases, the metastable state density first increases and then decreases,and the pressure value, at which the density maximum occurs, decreases with oxygen content increasing. Besides, adding a small fraction of oxygen into argon plasma will significantly dwindle the metastable state density as a result of quenching loss by oxygen molecules.展开更多
Direct absorption spectra of the 2v3 band of methane （CH4） from 6038 to 6050 cm 1 were studied at different low temperatures using a newly developed cryogenic cell in combination with a distributed feedback （DFB） ...Direct absorption spectra of the 2v3 band of methane （CH4） from 6038 to 6050 cm 1 were studied at different low temperatures using a newly developed cryogenic cell in combination with a distributed feedback （DFB） diode laser. The cryogenic cell can operate at any stabilized temperature ranging from room temperature down to 100 K with temperature fluctuation less than =t=1 K within 1 hour. In the present work, the CH4 spectra in the range of 6038-6050 cm-1 were recorded at 296, 266, 248, 223, 198, and 176 K. The lower state energy Ett and the rotational assignment of the angular momentum J were determined by a ＂2-low-temperature spectra method＂ using the spectra recorded at 198 and 176 K. The results were compared with the data from the GOSAT and the recently reported results from Campargue and co-workers using two spectra measured at room temperature and 81 K. We demonstrated that the use of a 2-low-temperature spectra method permits one to complete the Ett and J values missed in the previous studies.展开更多
Concentration time-histories of H20 were measured behind reflected shock waves during hydrogen combustion. Experiments were conducted at temperatures of 1117-1282 K, the equivalence ratios of 0.5 and 0.25, and a press...Concentration time-histories of H20 were measured behind reflected shock waves during hydrogen combustion. Experiments were conducted at temperatures of 1117-1282 K, the equivalence ratios of 0.5 and 0.25, and a pressure at 2 atm using a mixture of H2/O2 highly diluted with argon. H2O was monitored using tunable mid-infrared diode laser absorption at 2.55 μm （3920.09 cm-1）. These time-histories provide kinetic targets to test and refine reaction mechanisms for hydrogen. Comparisons were made with the predictions of four detailed kinetic mechanisms published in the last four years. Such comparisons of H2O concentration profiles indicate that the AramcoMech 2.0 mechanism yields the best agreement with the experimental data, while CRECK, San Diego, and HP-Mech mechanisms show significantly poor predictions. Reaction pathway analysis for hydrogen oxidation indicates that the reaction H ＋ OH ＋ M = H20 ＋ M is the key reaction for controlling the H2O formation by hydrogen oxidation. It is inferred that the discrepancy of the conversion percentage from H to H20 among these four mechanisms induces the difference of performance on H2O time-history predictions. This work demonstrates the potential of time-history measurement for validation of large reaction mechanisms.展开更多
In recent years, tighter regulation has been already enforced on harmful substances such as NOx, CO, and particles. Considering the above situation, it is important to monitor controlling factors of engine systems in ...In recent years, tighter regulation has been already enforced on harmful substances such as NOx, CO, and particles. Considering the above situation, it is important to monitor controlling factors of engine systems in order to improve efficiencies of their operations. As to car engines, an increasing concern in environmental issues such as air pollution, global warming and petroleum depletion has helped drive researches into various ways. Laser diagnostics has been applied to measure species concentration in the actual industrial fields. However there are several challenges to proceed in applying laser diagnostics to practical application. Especially stability of the measurement system is one of the most difficult issues. The purpose of this research is the development of a prompt measurement technique which can be applicable to various engine conditions. The Tunable Diode Laser Absorption Spectroscopy （TDLAS） using the hollow fiber has been developed to satisfy above requirements. By using a hollow fiber, misalignment of an optical axis and vulnerability of measurement environment such as vibration can be greatly reduced with sensitive and fast response features. It was demonstrated that this method can be applicable to measure gas compositions in engine exhaust with a range of millisecond response time. A sensitive method using tunable UV diode laser absorption spectroscopy was also discussed to detect NOx in exhausts.展开更多
A hydrogen peroxide[H_(2)O_(2)]detection system is demonstrated with multi-pass tunable diode laser absorption spectroscopy using a 75 m Herriott absorption cell.The system utilizes an~8μm continuous wave distributed...A hydrogen peroxide[H_(2)O_(2)]detection system is demonstrated with multi-pass tunable diode laser absorption spectroscopy using a 75 m Herriott absorption cell.The system utilizes an~8μm continuous wave distributed feedback quantum cascade laser[CW DFB-QCL]targeting a prominent H_(2)O_(2)line at 1253.1 cm^(-1)within the fundamental absorption band.A wavelength modulation spectroscopy with the first harmonic normalized second harmonic[WMS-2f/1f]detection method is employed to eliminate laser light intensity fluctuations.Calibration of the system is conducted by means of chemical titration to establish the correlation between the peak value of the 2f/1f signal and H_(2)O_(2)concentration.An Allan-Werle deviation analysis shows that a minimum detection limit[MDL]of 2.9 ppb[1 ppb=10^(-9)]for H_(2)O_(2)is achieved with an average time of 147 s.To the best of our knowledge,this is the lowest detection limit for H_(2)O_(2)at the wavenumber of 1253.1 cm^(-1).The system exhibits robust resistance to interference from other gases,especially water vapor[H_(2)O],making it suitable for measuring the residual concentration of H_(2)O_(2)post-sterilization and the concentration of H_(2)O_(2)in the atmosphere.展开更多
An optical spectrometer system based on 60 channels of fibers has been designed and employed to diagnose light emissions from laser–plasma interactions. The 60 fiber collectors cover an integrated solid angle of π, ...An optical spectrometer system based on 60 channels of fibers has been designed and employed to diagnose light emissions from laser–plasma interactions. The 60 fiber collectors cover an integrated solid angle of π, enabling the measurement of global energy losses in a symmetrical configuration. A detecting spectral range from ultraviolet to nearinfrared, with angular distribution, allows for the understanding of the physical mechanisms involving various plasma modes. Experimental measurements of scattered lights from a conical implosion driven by high-energy nanosecond laser beams at the Shenguang-II Upgrade facility have been demonstrated, serving as reliable diagnostics to characterize laser absorption and energy losses from laser–plasma instabilities. This compact diagnostic system can provide comprehensive insights into laser energy coupling in direct-drive inertial confinement fusion research, which are essential for studying the driving asymmetry and improving the implosion efficiencies.展开更多
A compact multipass cell with low fringes and high thermal stability is described. This cell is formed by two twisted cylindrical mirrors. The optical parameters are determined based on the selection criteria, which i...A compact multipass cell with low fringes and high thermal stability is described. This cell is formed by two twisted cylindrical mirrors. The optical parameters are determined based on the selection criteria, which include mirror filling efficiency, ~nterference fringes, and pattern stability. With a pattern of 174 passes, this cell gives a 22-m path length in a volume of 0.55 L. The results of an absorption measurement of oxygen at 13 091.7 cm-1 show that the fringe noise is lower than 6.54~10-4. The maximum allowed temperature change to keep the beam from exiting is 33 K, which indicates high stability against thermal drift.展开更多
With the advent of ultrashort high intensity laser pulses, laser absorption during the laser–solid interactions has received significant attention over the last two decades since it is related to a variety of applica...With the advent of ultrashort high intensity laser pulses, laser absorption during the laser–solid interactions has received significant attention over the last two decades since it is related to a variety of applications of high intensity lasers,including the hot electron production for fast ignition of fusion targets, table-top bright X-ray and gamma-ray sources,ion acceleration, compact neutron sources, and generally the creation of high energy density matters. Normally, some absorption mechanisms found for nanosecond long laser pulses also appear for ultrashort laser pulses. The peculiar aspects with ultrashort laser pulses are that their absorption depends significantly on the preplasma condition and the initial target structures. Meanwhile, relativistic nonlinearity and ponderomotive force associated with the laser pulses lead to new mechanisms or phenomena, which are usually not found with nanosecond long pulses. In this paper, we present an overview of the recent progress on the major absorption mechanisms in intense laser–solid interactions, where emphasis is paid to our related theory and simulation studies.展开更多
Aluminum alloy is used as the support of final optical assembly because of its excellent mechanical properties,which constitutes th e“skeleton”of high-power laser system.Stray light reflected by weak optical element...Aluminum alloy is used as the support of final optical assembly because of its excellent mechanical properties,which constitutes th e“skeleton”of high-power laser system.Stray light reflected by weak optical elements in high power laser system will fall on the inner wall frame of aluminum alloy,which will cause damage and produce impurity particles,polluting the entire optical system.However,the research on the damage mechanism and protection technology of aluminum alloy under the action of high-power laser system is still in the initial stage.This paper introduces the interaction mechanism between laser and materials,analyzes the laser damage mechanism of aluminum alloy from the perspective of plasma nano metal particle ablation,reviews the progress of laser-induced damage protection of aluminum alloy,and prospects the future research direction of laser absorption and damage protection technology of aluminum alloy under the action of high-energy laser.展开更多
We extend the third perturbation theory to study the polarization control behavior of the intermediate state absorption in Nd^（3＋）ions. The results show that coherent interference can occur between the single-photo...We extend the third perturbation theory to study the polarization control behavior of the intermediate state absorption in Nd^（3＋）ions. The results show that coherent interference can occur between the single-photon and three-photon excitation pathways, and depends on the central frequency of the femtosecond laser field. Moreover,single-photon and three-photon absorptions have different polarization control efficiencies, and the relative weight of three-photon absorption in the whole excitation processes can increase with increasing the laser intensity.Therefore, the enhancement or suppression of the intermediate state absorption can be realized and manipulated by properly designing the intensity and central frequency of the polarization modulated femtosecond laser field.This research can not only enrich theoretical research methods for the up-conversion luminescence manipulation of rare-earth ions, but also can provide a clear physical picture for understanding and controlling multi-photon absorption in a multiple energy level system.展开更多
The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control...The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.展开更多
In this study,the test subjects included the aluminum alloys 2A14 and 5A06,as well as the welding wires ER2319 and ER5356,single laser welding,laser welding with filler wire,laser metal inert gas(laser-MIG)hybrid weld...In this study,the test subjects included the aluminum alloys 2A14 and 5A06,as well as the welding wires ER2319 and ER5356,single laser welding,laser welding with filler wire,laser metal inert gas(laser-MIG)hybrid welding and laser-MIG hybrid welding with filler wire were carried out respectively to research the influence of aluminum alloy base material and welding wire on weld forming charac-teristics.The results show that:under the same test conditions,the penetration of the base material 5A06 is greater than that of 2A14,the maximum is about 51.3%,and the penetration filling ER5356 is greater than that of ER2319,the maximum is about 32.2%;for 2A14 alu-minum alloy,the penetration is basically unchanged after filling with ER5356,and there is a relatively large decrease after filling ER2319,the maximum is about 21.2%;for 5A06 aluminum alloy,the penetration decreases after filling both kinds of welding wire,the penetration achieved with filler wire ER2319 is lower than that of ER5356.At the same time,through the process of laser absorption in different metal materials,it was found that the differences in material composition led to different laser absorption rates,resulting in different energy utiliza-tion,which is an important reason for the correlation between aluminum alloy materials and laser-MIG hybrid welding with filler wire.展开更多
We present a differential laser absorption spectroscopy(DLAS)system operating at 1550 nm for rapid and sensitive gas concentration measurements.A dual-wavelength toggling mechanism is presented,which significantly red...We present a differential laser absorption spectroscopy(DLAS)system operating at 1550 nm for rapid and sensitive gas concentration measurements.A dual-wavelength toggling mechanism is presented,which significantly reduces data processing,hence supporting a high update rate and data robustness against fast-changing environmental conditions.We showcase the ability to toggle between two wavelengths separated by 90 pm in 14μs and with minimal chirp(~1 pm),facilitating sensitive DLAS measurements at 8 kHz update rate.This performance is achieved by driving a 1550 nm diode laser with a modified square-wave current pulse,overcoming the thermal time constant limited wavelength-modulation response of the diode laser.A sensitive feedback mechanism ensures excellent long-term wavelength stability better than 1.4 pm peak-to-peak at 8 kHz toggling over 20 h,As a performance test,we measured the volumetric ratio(VMR)of hydrogen cyanide(HCN)gas in a fiber-coupled gas cell with lessthan 0.2%peak-to-peak variation over 20 h at 40 Hz.A best sensitivity in VMR of 8×10^(-6) was achieved at 25 ms integration time.The simplicity and high update rate of our system make it well-suited for gas monitoring in dynamic atmospheric and industrial environments.Further,it offers potential utility in applications requiring precise wavelength control,such as injection seeding of pulsed lasers.A simple analytical model is derived,which,in detail,supports the experimental results,hence offering a tool for future design optimization.展开更多
Because methane is flammable and explosive,the detection process is time-consuming and dangerous,and it is difficult to obtain labeled data.In order to reduce the dependence on marker data when detecting methane conce...Because methane is flammable and explosive,the detection process is time-consuming and dangerous,and it is difficult to obtain labeled data.In order to reduce the dependence on marker data when detecting methane concentration using tunable diode laser absorption spectroscopy(TDLAS)technology,this paper designs a methane gas acquisition platform based on TDLAS and proposes a methane gas concentration detection model based on semi-supervised learning.Firstly,the methane gas is feature extracted,and then semi-supervised learning is introduced to select the optimal feature combination;subsequently,the traditional whale optimization algorithm is improved to optimize the parameters of the random forest to detect the methane gas concentration.The results show that the model is not only able to select the optimal feature combination under limited labeled data,but also has an accuracy of 94.25%,which is better than the traditional model,and is robust in terms of parameter optimization.展开更多
To provide advanced diagnostic techniques for diagnosing the outlet temperature distribution and species concentrations of future advanced combustors,this study focuses on a dual-swirl single-dome rectangular combusto...To provide advanced diagnostic techniques for diagnosing the outlet temperature distribution and species concentrations of future advanced combustors,this study focuses on a dual-swirl single-dome rectangular combustor.Through the integration of multiple diagnostics,simultaneous measurement of outlet temperature distribution and species concentrations was achieved.The study validates the engineering applicability of these simultaneous measurements using tungsten-rhenium(W-Re)thermocouples and Coherent Anti-Stokes Raman Scattering(CARS),CARS and Tunable Diode Laser Absorption Spectroscopy(TDLAS),as well as Gas Analysis(GA)and Mass Spectrometry(MS).The results demonstrate that measurements by thermocouples and CARS exhibit good consistency and repeatability,with a relative deviation of less than 4%,fully meeting the requirements of engineering experiments.The spatial distribution reconstruction results of TDLAS can reflect the temperature distribution characteristics at the combustor outlet.Temperature comparison between TDLAS and CARS at single-point positions shows consistent results,with a relative deviation of less than 11%and 7%under both conditions,respectively.Simultaneous measurements by integrating GA and MS show high engineering applicability for the first time,meeting the requirements for measuring both inorganic species and free radicals at the combustor outlet.Under C_(1)condition,the relative deviations of four key species(Unburned Hydrocarbon(UHC),NO,O_(2),and CO_(2))remain within 2%,while that of NO_(2)is slightly higher at approximately 8%.Under C_(2)condition,the overall deviations increase for most species,with only O_(2)and CO_(2)maintaining relatively low deviations.The primary species of UHCs at the combustor outlet under both conditions are small molecular hydrocarbons(C_(3)-C_(8))and RO_(2)radicals,accounting for over 90%of total UHC.Specifically,RO_(2)species(R is C_(1)-C_(2)alkyl groups)are the predominant species,accounting for 74.3%and 82.1%of total RO_(2)under both conditions,respectively.These integrated diagnostic methods for temperature and species concentrations at the combustor outlet serve as a crucial reference for its engineering applications.展开更多
SmAlO3 powders were successfully synthesized through the citrate sol-gel combustion method. The phase evolution of the prepared powders were characterized using thermal gravimetric （TG） analysis, differential scanni...SmAlO3 powders were successfully synthesized through the citrate sol-gel combustion method. The phase evolution of the prepared powders were characterized using thermal gravimetric （TG） analysis, differential scanning calorimetry （DSC） analysis and Fourier transform infrared spectroscopy （FTIR）. X-ray diffraction （XRD） was applied to examine the purity of the powders. The re-flective properties of SmAlO3 with changing temperatures were investigated by ultraviolet-visible near-infrared spectrophotometer （UVPC） specular reflection spectrum. The results displayed that pure SmAlO3 phase with preferable reflectivity at 1.06μm could be obtained at 900 oC for 2 h. Furthermore, the reflectivity of SmAlO3 at various temperatures from-40 to 500 oC transformed within ±0.1%, and all maintained below 1%at 1.06μm. The absorbance of SmAlO3 in the resin solution was 2.134 and the moral absorption coefficient was about 384.8 in the work. The study indicated that SmAlO3 powders may be a promising kind of heat resistant absorb-ing material for 1.06μm laser defense, which could be further applied to laser absorbing coatings with a wide range of temperatures.展开更多
基金supported by the Presidential Foundation of China Academy of Engineering Physics (No. YZJJLX 2018011)National Natural Science Foundation of China (Nos. 11775204, 11734013, 12105269 and 12004351)
文摘In indirect-driven laser fusion experiments,the movement of the laser absorption layer will distort the radiation uniformity on the capsule.The gold foam has advantages in symmetry control and lowering wall plasma blowoff when used in an inertial confinement fusion(ICF)hohlraum.This work investigates the motion of the laser absorption cutoff position using lowdensity foam gold walls.It is found that the motion of the laser absorption cutoff position can be significantly mitigated through optimal initial low density,tailored to a specific laser shape.For a short square laser pulse,the laser absorption cutoff position remains almost stationary at an initial density of approximately 0.6 g cm^(-3).For a long-shaped laser pulse,the minimal motion of the laser absorption cutoff position is observed at an initial density of about 0.1 g cm^(-3).This approach allows for the adjustment of the symmetry of the hohlraum radiation source.The insights gained from this study serve as a crucial reference for optimizing the hohlraum wall density.
基金surpported by the National Natural Science Foundation of China(No.52206222,No.22227901)Aero Engine and Gas Turbine Basic Science Centre Project(P2023-B-V-002-001).
文摘The measurement of the combustion characteristics of a single biomass particle is essential for studying massive biofuel energy conversion process;however,it is challenging due to the small physical scale of the biomass particle flame.In this work,we report an investigation of the combustion behavior of single lignin and single cellulose particle through CO_(2)absorption spectroscopy and high-speed photography.The biomass samples are prepared with an initial diameter of about 1.0 mm and are ignited on a heating plate placed inside a multi-pass absorption cell.The shape and size transformation of single biomass particle are recorded through high-speed photography,and the combustion temperature and CO_(2)column densities are measured through laser absorption spectroscopy at 4.172µm.We find that the maximum combustion temperatures are 1662±38 K and 1569±26 K for lignin and cellulose particle,respectively.Besides,we find that CO_(2)generation precedes the generation of visible volatile flame for cellulose particle.While for lignin particle,the CO_(2)generation is found to be almost at the same time as its volatile combustion stage begins.The measurement technique and results presented in this work are of practical interest for biomass combustion studies and arc meaningful for the development of biomass thermal conversion mode.
文摘Exhaust gas temperature is an important factor in NOx, THC and PM emissions of engines. Especially 2D temperature and concentration distribution plays an important role for the engine efficiency. A thermocouple is intrinsically a point temperature measurement method and noncontact 2D temperature distribution cannot be attained by thermocouples. Recently, as a measurement technique with high sensitivity and high response, laser diagnostics has been developed and applied to the actual engine combustions. With these engineering developments, transient phenomena such as start-ups and load changes in engines have been gradually elucidated in various conditions. In this study, the theoretical and experimental research has been conducted in order to develop the noncontact and fast response 2D temperature and concentration distribution measurement method. The method is based on a Computed Tomography （CT） method using absorption spectra of water vapor at 1388 nm. It has been demonstrated that the method has been successfully applied to engine exhausts to measure 2D temperature distributions.
基金Project supported by the National Science Foundation of China (Grant Nos 60578015 and 60208004)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No 20050288025)
文摘In this paper, the compositions in a laser absorption region can be determined from the experiment of laser impulse coupling. When the ambient pressure varies from 9325 to 33325Pa, the compositions are vapour and plasma; while from 35325 to 101325Pa, they are ambient air and plasma. By analysing the relation between the degree of compression and the ambient pressure, the compositions can be determined and the variation of plasma can be explained.
基金supported by the National Natural Science Foundation of China(Grant Nos.11335004,11722541,11675039,and 11747153)the Important National Science and Technology Specific Project,China(Grant No.2011ZX02403-001)
文摘Densities of Ar metastable states 1s5 and 1s3 are measured by using the tunable diode laser absorption spectroscopy（TDLAS） in Ar and Ar/O2 mixture dual-frequency capacitively coupled plasma（DF-CCP）. We investigate the effects of high-frequency（HF, 60 MHz） power, low-frequency（LF, 2 MHz） power, and working pressure on the density of Ar metastable states for three different gas components（0%, 5%, and 10% oxygen mixed in argon）. The dependence of Ar metastable state density on the oxygen content is also studied at different working pressures. It is found that densities of Ar metastable states in discharges with different gas components exhibit different behaviors as HF power increases. With the increase of HF power, the metastable density increases rapidly at the initial stage, and then tends to be saturated at a higher HF power. With a small fraction（5% or 10%） of oxygen added in argon plasma, a similar change of the Ar metastable density with HF power can be observed, but the metastable density is saturated at a higher HF power than in the pure argon discharge. In the DF-CCP, the metastable density is found to be higher than in a single frequency discharge, and has weak dependence on LF power. As working pressure increases, the metastable state density first increases and then decreases,and the pressure value, at which the density maximum occurs, decreases with oxygen content increasing. Besides, adding a small fraction of oxygen into argon plasma will significantly dwindle the metastable state density as a result of quenching loss by oxygen molecules.
基金Project supported by the National Natural Science Foundation of China(Grant No.41175036)
文摘Direct absorption spectra of the 2v3 band of methane （CH4） from 6038 to 6050 cm 1 were studied at different low temperatures using a newly developed cryogenic cell in combination with a distributed feedback （DFB） diode laser. The cryogenic cell can operate at any stabilized temperature ranging from room temperature down to 100 K with temperature fluctuation less than =t=1 K within 1 hour. In the present work, the CH4 spectra in the range of 6038-6050 cm-1 were recorded at 296, 266, 248, 223, 198, and 176 K. The lower state energy Ett and the rotational assignment of the angular momentum J were determined by a ＂2-low-temperature spectra method＂ using the spectra recorded at 198 and 176 K. The results were compared with the data from the GOSAT and the recently reported results from Campargue and co-workers using two spectra measured at room temperature and 81 K. We demonstrated that the use of a 2-low-temperature spectra method permits one to complete the Ett and J values missed in the previous studies.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFB0202400 and 2017YFB0202401)
文摘Concentration time-histories of H20 were measured behind reflected shock waves during hydrogen combustion. Experiments were conducted at temperatures of 1117-1282 K, the equivalence ratios of 0.5 and 0.25, and a pressure at 2 atm using a mixture of H2/O2 highly diluted with argon. H2O was monitored using tunable mid-infrared diode laser absorption at 2.55 μm （3920.09 cm-1）. These time-histories provide kinetic targets to test and refine reaction mechanisms for hydrogen. Comparisons were made with the predictions of four detailed kinetic mechanisms published in the last four years. Such comparisons of H2O concentration profiles indicate that the AramcoMech 2.0 mechanism yields the best agreement with the experimental data, while CRECK, San Diego, and HP-Mech mechanisms show significantly poor predictions. Reaction pathway analysis for hydrogen oxidation indicates that the reaction H ＋ OH ＋ M = H20 ＋ M is the key reaction for controlling the H2O formation by hydrogen oxidation. It is inferred that the discrepancy of the conversion percentage from H to H20 among these four mechanisms induces the difference of performance on H2O time-history predictions. This work demonstrates the potential of time-history measurement for validation of large reaction mechanisms.
文摘In recent years, tighter regulation has been already enforced on harmful substances such as NOx, CO, and particles. Considering the above situation, it is important to monitor controlling factors of engine systems in order to improve efficiencies of their operations. As to car engines, an increasing concern in environmental issues such as air pollution, global warming and petroleum depletion has helped drive researches into various ways. Laser diagnostics has been applied to measure species concentration in the actual industrial fields. However there are several challenges to proceed in applying laser diagnostics to practical application. Especially stability of the measurement system is one of the most difficult issues. The purpose of this research is the development of a prompt measurement technique which can be applicable to various engine conditions. The Tunable Diode Laser Absorption Spectroscopy （TDLAS） using the hollow fiber has been developed to satisfy above requirements. By using a hollow fiber, misalignment of an optical axis and vulnerability of measurement environment such as vibration can be greatly reduced with sensitive and fast response features. It was demonstrated that this method can be applicable to measure gas compositions in engine exhaust with a range of millisecond response time. A sensitive method using tunable UV diode laser absorption spectroscopy was also discussed to detect NOx in exhausts.
基金supported by the“Pioneer”and“Leading Goose”R&D Program of Zhejiang(Nos.2022C03065,2022C030842022C03162)+3 种基金the Primary Research and Development Plan of Zhejiang Province(No.2023C03014)the Key Research and Development Program of Zhejiang Province(No.2022C03037)the Science and Technology Program of the State Administration of Market Supervision(No.2023MK049)the Science and Technology Program of Market Supervision Administration of Zhejiang Province(Nos.QN2023419 and QN2023420)。
文摘A hydrogen peroxide[H_(2)O_(2)]detection system is demonstrated with multi-pass tunable diode laser absorption spectroscopy using a 75 m Herriott absorption cell.The system utilizes an~8μm continuous wave distributed feedback quantum cascade laser[CW DFB-QCL]targeting a prominent H_(2)O_(2)line at 1253.1 cm^(-1)within the fundamental absorption band.A wavelength modulation spectroscopy with the first harmonic normalized second harmonic[WMS-2f/1f]detection method is employed to eliminate laser light intensity fluctuations.Calibration of the system is conducted by means of chemical titration to establish the correlation between the peak value of the 2f/1f signal and H_(2)O_(2)concentration.An Allan-Werle deviation analysis shows that a minimum detection limit[MDL]of 2.9 ppb[1 ppb=10^(-9)]for H_(2)O_(2)is achieved with an average time of 147 s.To the best of our knowledge,this is the lowest detection limit for H_(2)O_(2)at the wavenumber of 1253.1 cm^(-1).The system exhibits robust resistance to interference from other gases,especially water vapor[H_(2)O],making it suitable for measuring the residual concentration of H_(2)O_(2)post-sterilization and the concentration of H_(2)O_(2)in the atmosphere.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Nos.XDA25010100,XDA25010300 and XDA25030100)in part by the National Natural Science Foundation of China(No.12105359)the Chinese Academy of Sciences Youth Interdisciplinary Team(No.JCTD-2022-05)
文摘An optical spectrometer system based on 60 channels of fibers has been designed and employed to diagnose light emissions from laser–plasma interactions. The 60 fiber collectors cover an integrated solid angle of π, enabling the measurement of global energy losses in a symmetrical configuration. A detecting spectral range from ultraviolet to nearinfrared, with angular distribution, allows for the understanding of the physical mechanisms involving various plasma modes. Experimental measurements of scattered lights from a conical implosion driven by high-energy nanosecond laser beams at the Shenguang-II Upgrade facility have been demonstrated, serving as reliable diagnostics to characterize laser absorption and energy losses from laser–plasma instabilities. This compact diagnostic system can provide comprehensive insights into laser energy coupling in direct-drive inertial confinement fusion research, which are essential for studying the driving asymmetry and improving the implosion efficiencies.
基金supported by the National Key Scientifc Instrument and Equipment Development Project under Grant No.2012YQ22011902
文摘A compact multipass cell with low fringes and high thermal stability is described. This cell is formed by two twisted cylindrical mirrors. The optical parameters are determined based on the selection criteria, which include mirror filling efficiency, ~nterference fringes, and pattern stability. With a pattern of 174 passes, this cell gives a 22-m path length in a volume of 0.55 L. The results of an absorption measurement of oxygen at 13 091.7 cm-1 show that the fringe noise is lower than 6.54~10-4. The maximum allowed temperature change to keep the beam from exiting is 33 K, which indicates high stability against thermal drift.
基金Project supported by the National Basic Research Program of China(Grant No.2013CBA01504)the National Natural Science Foundation of China(Grant Nos.11421064,11129503,11374209,and 11374210)
文摘With the advent of ultrashort high intensity laser pulses, laser absorption during the laser–solid interactions has received significant attention over the last two decades since it is related to a variety of applications of high intensity lasers,including the hot electron production for fast ignition of fusion targets, table-top bright X-ray and gamma-ray sources,ion acceleration, compact neutron sources, and generally the creation of high energy density matters. Normally, some absorption mechanisms found for nanosecond long laser pulses also appear for ultrashort laser pulses. The peculiar aspects with ultrashort laser pulses are that their absorption depends significantly on the preplasma condition and the initial target structures. Meanwhile, relativistic nonlinearity and ponderomotive force associated with the laser pulses lead to new mechanisms or phenomena, which are usually not found with nanosecond long pulses. In this paper, we present an overview of the recent progress on the major absorption mechanisms in intense laser–solid interactions, where emphasis is paid to our related theory and simulation studies.
基金Project(AUGA5630112723)supported by the Assistant Professor Research Initiation Project of Harbin Institute of Technology,China。
文摘Aluminum alloy is used as the support of final optical assembly because of its excellent mechanical properties,which constitutes th e“skeleton”of high-power laser system.Stray light reflected by weak optical elements in high power laser system will fall on the inner wall frame of aluminum alloy,which will cause damage and produce impurity particles,polluting the entire optical system.However,the research on the damage mechanism and protection technology of aluminum alloy under the action of high-power laser system is still in the initial stage.This paper introduces the interaction mechanism between laser and materials,analyzes the laser damage mechanism of aluminum alloy from the perspective of plasma nano metal particle ablation,reviews the progress of laser-induced damage protection of aluminum alloy,and prospects the future research direction of laser absorption and damage protection technology of aluminum alloy under the action of high-energy laser.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51132004,11474096,11604199,U1704145 and 11747101the Science and Technology Commission of Shanghai Municipality under Grant No 14JC1401500+1 种基金the Henan Provincial Natural Science Foundation of China under Grant No 182102210117the Higher Education Key Program of He’nan Province of China under Grant Nos 17A140025 and 16A140030
文摘We extend the third perturbation theory to study the polarization control behavior of the intermediate state absorption in Nd^（3＋）ions. The results show that coherent interference can occur between the single-photon and three-photon excitation pathways, and depends on the central frequency of the femtosecond laser field. Moreover,single-photon and three-photon absorptions have different polarization control efficiencies, and the relative weight of three-photon absorption in the whole excitation processes can increase with increasing the laser intensity.Therefore, the enhancement or suppression of the intermediate state absorption can be realized and manipulated by properly designing the intensity and central frequency of the polarization modulated femtosecond laser field.This research can not only enrich theoretical research methods for the up-conversion luminescence manipulation of rare-earth ions, but also can provide a clear physical picture for understanding and controlling multi-photon absorption in a multiple energy level system.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51132004,11474096 and 11604199the Science and Technology Commission of Shanghai Municipality under Grant No 14JC1401500the Higher Education Key Program of He'nan Province under Grant Nos 17A140025 and 16A140030
文摘The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.
基金supported by the Henan Science and Technology Plan Joint Fund Project(Key Project)(203ZP20230007).
文摘In this study,the test subjects included the aluminum alloys 2A14 and 5A06,as well as the welding wires ER2319 and ER5356,single laser welding,laser welding with filler wire,laser metal inert gas(laser-MIG)hybrid welding and laser-MIG hybrid welding with filler wire were carried out respectively to research the influence of aluminum alloy base material and welding wire on weld forming charac-teristics.The results show that:under the same test conditions,the penetration of the base material 5A06 is greater than that of 2A14,the maximum is about 51.3%,and the penetration filling ER5356 is greater than that of ER2319,the maximum is about 32.2%;for 2A14 alu-minum alloy,the penetration is basically unchanged after filling with ER5356,and there is a relatively large decrease after filling ER2319,the maximum is about 21.2%;for 5A06 aluminum alloy,the penetration decreases after filling both kinds of welding wire,the penetration achieved with filler wire ER2319 is lower than that of ER5356.At the same time,through the process of laser absorption in different metal materials,it was found that the differences in material composition led to different laser absorption rates,resulting in different energy utiliza-tion,which is an important reason for the correlation between aluminum alloy materials and laser-MIG hybrid welding with filler wire.
文摘We present a differential laser absorption spectroscopy(DLAS)system operating at 1550 nm for rapid and sensitive gas concentration measurements.A dual-wavelength toggling mechanism is presented,which significantly reduces data processing,hence supporting a high update rate and data robustness against fast-changing environmental conditions.We showcase the ability to toggle between two wavelengths separated by 90 pm in 14μs and with minimal chirp(~1 pm),facilitating sensitive DLAS measurements at 8 kHz update rate.This performance is achieved by driving a 1550 nm diode laser with a modified square-wave current pulse,overcoming the thermal time constant limited wavelength-modulation response of the diode laser.A sensitive feedback mechanism ensures excellent long-term wavelength stability better than 1.4 pm peak-to-peak at 8 kHz toggling over 20 h,As a performance test,we measured the volumetric ratio(VMR)of hydrogen cyanide(HCN)gas in a fiber-coupled gas cell with lessthan 0.2%peak-to-peak variation over 20 h at 40 Hz.A best sensitivity in VMR of 8×10^(-6) was achieved at 25 ms integration time.The simplicity and high update rate of our system make it well-suited for gas monitoring in dynamic atmospheric and industrial environments.Further,it offers potential utility in applications requiring precise wavelength control,such as injection seeding of pulsed lasers.A simple analytical model is derived,which,in detail,supports the experimental results,hence offering a tool for future design optimization.
基金supported by the Ministry of Education Chunhui Program of China(No.HZKY20220304).
文摘Because methane is flammable and explosive,the detection process is time-consuming and dangerous,and it is difficult to obtain labeled data.In order to reduce the dependence on marker data when detecting methane concentration using tunable diode laser absorption spectroscopy(TDLAS)technology,this paper designs a methane gas acquisition platform based on TDLAS and proposes a methane gas concentration detection model based on semi-supervised learning.Firstly,the methane gas is feature extracted,and then semi-supervised learning is introduced to select the optimal feature combination;subsequently,the traditional whale optimization algorithm is improved to optimize the parameters of the random forest to detect the methane gas concentration.The results show that the model is not only able to select the optimal feature combination under limited labeled data,but also has an accuracy of 94.25%,which is better than the traditional model,and is robust in terms of parameter optimization.
基金support of the National Major Science and Technology Projects of China(No.J2019-V-0005-0096)the National Key Research and Development Program of China(No.2020YFA0405700).
文摘To provide advanced diagnostic techniques for diagnosing the outlet temperature distribution and species concentrations of future advanced combustors,this study focuses on a dual-swirl single-dome rectangular combustor.Through the integration of multiple diagnostics,simultaneous measurement of outlet temperature distribution and species concentrations was achieved.The study validates the engineering applicability of these simultaneous measurements using tungsten-rhenium(W-Re)thermocouples and Coherent Anti-Stokes Raman Scattering(CARS),CARS and Tunable Diode Laser Absorption Spectroscopy(TDLAS),as well as Gas Analysis(GA)and Mass Spectrometry(MS).The results demonstrate that measurements by thermocouples and CARS exhibit good consistency and repeatability,with a relative deviation of less than 4%,fully meeting the requirements of engineering experiments.The spatial distribution reconstruction results of TDLAS can reflect the temperature distribution characteristics at the combustor outlet.Temperature comparison between TDLAS and CARS at single-point positions shows consistent results,with a relative deviation of less than 11%and 7%under both conditions,respectively.Simultaneous measurements by integrating GA and MS show high engineering applicability for the first time,meeting the requirements for measuring both inorganic species and free radicals at the combustor outlet.Under C_(1)condition,the relative deviations of four key species(Unburned Hydrocarbon(UHC),NO,O_(2),and CO_(2))remain within 2%,while that of NO_(2)is slightly higher at approximately 8%.Under C_(2)condition,the overall deviations increase for most species,with only O_(2)and CO_(2)maintaining relatively low deviations.The primary species of UHCs at the combustor outlet under both conditions are small molecular hydrocarbons(C_(3)-C_(8))and RO_(2)radicals,accounting for over 90%of total UHC.Specifically,RO_(2)species(R is C_(1)-C_(2)alkyl groups)are the predominant species,accounting for 74.3%and 82.1%of total RO_(2)under both conditions,respectively.These integrated diagnostic methods for temperature and species concentrations at the combustor outlet serve as a crucial reference for its engineering applications.
基金supported by Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘SmAlO3 powders were successfully synthesized through the citrate sol-gel combustion method. The phase evolution of the prepared powders were characterized using thermal gravimetric （TG） analysis, differential scanning calorimetry （DSC） analysis and Fourier transform infrared spectroscopy （FTIR）. X-ray diffraction （XRD） was applied to examine the purity of the powders. The re-flective properties of SmAlO3 with changing temperatures were investigated by ultraviolet-visible near-infrared spectrophotometer （UVPC） specular reflection spectrum. The results displayed that pure SmAlO3 phase with preferable reflectivity at 1.06μm could be obtained at 900 oC for 2 h. Furthermore, the reflectivity of SmAlO3 at various temperatures from-40 to 500 oC transformed within ±0.1%, and all maintained below 1%at 1.06μm. The absorbance of SmAlO3 in the resin solution was 2.134 and the moral absorption coefficient was about 384.8 in the work. The study indicated that SmAlO3 powders may be a promising kind of heat resistant absorb-ing material for 1.06μm laser defense, which could be further applied to laser absorbing coatings with a wide range of temperatures.
