The use of broadband laser technology is a novel approach for inhibiting processes related to laser plasma interactions(LPIs).In this study,several preliminary experiments into broadband-laser-driven LPIs are carried ...The use of broadband laser technology is a novel approach for inhibiting processes related to laser plasma interactions(LPIs).In this study,several preliminary experiments into broadband-laser-driven LPIs are carried out using a newly established hundreds-of-joules broadband second-harmonic-generation laser facility.Through direct comparison with LPI results for a traditional narrowband laser,the actual LPI-suppression effect of the broadband laser is shown.The broadband laser had a clear suppressive effect on both back-stimulated Raman scattering and back-stimulated Brillouin scattering at laser intensities below 1×10^(15) W cm^(−2).An abnormal hot-electron phenomenon is also investigated,using targets of different thicknesses.展开更多
Monochromatic x-ray imaging is an essential method for plasma diagnostics related to density information.Large-field high-resolution monochromatic imaging of a He-like iron(Fe XXV)Kαcharacteristic line(6.701 keV)for ...Monochromatic x-ray imaging is an essential method for plasma diagnostics related to density information.Large-field high-resolution monochromatic imaging of a He-like iron(Fe XXV)Kαcharacteristic line(6.701 keV)for laser plasma diagnostics was achieved using a developed toroidal crystal x-ray imager.A high-index crystal orientation Ge(531)wafer with a Bragg angle of 75.37°and the toroidal substrate were selected to obtain sufficient diffraction efficiency and compensate for astigmatism under oblique incidence.A precise offline assembly method of the toroidal crystal imager based on energy substitution was proposed,and a spatial resolution of 3-7μm was obtained by toroidal crystal imaging of a 600 line-pairs/inch Au grid within an object field of view larger than 1.0 mm.The toroidal crystal x-ray imager has been successfully tested via side-on backlight imaging experiments of the sinusoidal modulation target and a 1000 line-pairs/inch Au grid with a linewidth of 5μm using an online alignment method based on dual positioning balls to indicate the target and backlighter.This paper describes the optical design,adjustment method,and experimental results of a toroidal crystal system in a laboratory and laser facility.展开更多
AmpliHcation of spontaneous emissions at 19.6,23.2 and 23.6 nm have been observed by a “ultiple-Target Series Coupling”design in Ge plasma,.The combined length for four targets is up to 56mm.The gain length product(...AmpliHcation of spontaneous emissions at 19.6,23.2 and 23.6 nm have been observed by a “ultiple-Target Series Coupling”design in Ge plasma,.The combined length for four targets is up to 56mm.The gain length product(GL)of small signal is up to 18 for both lines at 23.2 and 23.6 nmt and the effective GL is 16.4 and 15.7 for these two lines respectively.This two lines are obviously tending to saturation.The divergence of x-ray laser beam is about 4 mrad.展开更多
We present particle-in-cell(PIC)simulations of laser plasma instabilities(LPIs)with a laser pulse duration of a few picoseconds.The simulation parameters are appropriate to the planar-target LPI experimental condition...We present particle-in-cell(PIC)simulations of laser plasma instabilities(LPIs)with a laser pulse duration of a few picoseconds.The simulation parameters are appropriate to the planar-target LPI experimental conditions on SG-II.In this regime,the plasmas are characterized by a long electron density scale length and a large electron density range.It is found that when the incident laser intensity is well above its backward stimulated Raman scattering(backward SRS,BSRS)threshold,the backscattered light via the primary BSRS is intense enough to excite secondary SRS(Re-SRS)in the region below one-ninth of the critical density of the incident laser.The daughter light wave via the secondary BSRS(Re-BSRS)is amplified as it propagates toward the higher-density region in the bath of broadband light generated through the primary BSRS process.A higher intensity of the incident laser not only increases the amplitude of the BSRS light but also increases the convective amplification lengths of the Re-BSRS modes by broadening the spectrum of the BSRS light.Convective amplification of Re-BSRS causes pump depletion of the primary BSRS light and may lead to an underestimate of the primary BSRS level in SP-LPI experiments.Asignificant fraction of the generation of energetic electrons is strongly correlated with the Re-BSRS modes and should be considered as a significant energy loss.展开更多
The X-ray spectrometer used in high-energy-density plasma experiments generally requires both broad X-ray energy coverage and high temporal, spatial, and spectral resolutions for overcoming the difficulties imposed by...The X-ray spectrometer used in high-energy-density plasma experiments generally requires both broad X-ray energy coverage and high temporal, spatial, and spectral resolutions for overcoming the difficulties imposed by the X-ray background, debris, and mechanical shocks. By using an elliptical crystal together with a streak camera, we resolve this issue at the SG-II laser facility. The carefully designed elliptical crystal has a broad spectral coverage with high resolution, strong rejection of the diffuse and/or fluorescent background radiation, and negligible source broadening for extended sources.The spectra that are Bragg reflected(23?< θ < 38?) from the crystal are focused onto a streak camera slit 18 mm long and about 80 μm wide, to obtain a time-resolved spectrum. With experimental measurements, we demonstrate that the quartz(1011) elliptical analyzer at the SG-II laser facility has a single-shot spectral range of(4.64–6.45) keV, a typical spectral resolution of E/?E = 560, and an enhanced focusing power in the spectral dimension. For titanium(Ti) data, the lines of interest show a distribution as a function of time and the temporal variations of the He-α and Li-like Ti satellite lines and their spatial profiles show intensity peak red shifts. The spectrometer sensitivity is illustrated with a temporal resolution of better than 25 ps, which satisfies the near-term requirements of high-energy-density physics experiments.展开更多
Several experiments are performed on the ShenGuang-II laser facility to investigate an x-ray source and test radiography concepts.X-ray lines emitted from laser-produced plasmas are the most practical means of generat...Several experiments are performed on the ShenGuang-II laser facility to investigate an x-ray source and test radiography concepts.X-ray lines emitted from laser-produced plasmas are the most practical means of generating these high intensity sources.By using a time-integrated space-resolved keV spectroscope and pinhole camera,potential helium-like titanium Kα x-ray backlighting (radiography) line source is studied as a function of laser wavelength,ratio of pre-pulse intensity to main pulse intensity,and laser intensity (from 7.25 to～11.3×10 15 W/cm 2).One-dimensional radiography using a grid consisting of 5 μm Au wires on 16 μm period and the pinhole-assisted point projection is tested.The measurements show that the size of the helium-like titanium Kα source from a simple foil target is larger than 100 μm,and relative x-ray line emission conversion efficiency ξ x from the incident laser light energy to heliumlike titanium K-shell spectrum increases significantly with pre-pulse intensity increasing,increases rapidly with laser wavelength decreasing,and increases moderately with main laser intensity increasing.It is also found that a gold gird foils can reach an imaging resolution better than 5-μm featured with high contrast.It is further demonstrated that the pinhole-assisted point projection at such a level will be a novel two-dimensional imaging diagnostic technique for inertial confinement fusion experiments.展开更多
The use of low-coherence light is expected to be one of the effective ways to suppress or even eliminate the laser–plasma instabilities that arise in attempts to achieve inertial confinement fusion.In this paper,a re...The use of low-coherence light is expected to be one of the effective ways to suppress or even eliminate the laser–plasma instabilities that arise in attempts to achieve inertial confinement fusion.In this paper,a review of low-coherence high-power laser drivers and related key techniques is first presented.Work at typical low-coherence laser facilities,including Gekko XII,PHEBUS,Pharos III,and Kanal-2 is described.The many key techniques that are used in the research and development of low-coherence laser drivers are described and analyzed,including low-coherence source generation,amplification,harmonic conversion,and beam smoothing of low-coherence light.Then,recent progress achieved by our group in research on a broadband low-coherence laser driver is presented.During the development of our low-coherence high-power laser facility,we have proposed and implemented many key techniques for working with low-coherence light,including source generation,efficient amplification and propagation,harmonic conversion,beam smoothing,and precise beam control.Based on a series of technological breakthroughs,a kilojoule low-coherence laser driver named Kunwu with a coherence time of only 300 fs has been built,and the first round of physical experiments has been completed.This high-power laser facility provides not only a demonstration and verification platform for key techniques and system integration of a low-coherence laser driver,but also a new type of experimental platform for research into,for example,high-energy-density physics and,in particular,laser–plasma interactions.展开更多
An experiment with thin titanium foils irradiated by two pulses delayed in time is conducted on the Shenguang-II laser facility.A prepulse induces an underdense plasma,2-ns later a main pulse(λ L = 0.35 μm,E L ≈ 12...An experiment with thin titanium foils irradiated by two pulses delayed in time is conducted on the Shenguang-II laser facility.A prepulse induces an underdense plasma,2-ns later a main pulse(λ L = 0.35 μm,E L ≈ 120 J,τ L ≈ 100 ps) is injected into the underdense plasma and produces strong line emission from the titanium K shell(i.e.,He α at 4.7 keV).Data show that the intensity of 4.7-keV X-ray emission with the prepulse is approximately twice more than without the prepulse,and can be used as a backlighting source satisfying the diagnostic requirements for dense plasma probing.Highquality plasma images are obtained with the backlighting 4.7-keV X-rays in a Rayleigh-Taylor hydrodynamic instability experiment.展开更多
A simultaneous high-resolution x-ray backlighting and self-emission imaging method for laser-produced plasma diagnostics is developed in which two Kirkpatrick–Baez imaging channels for high-energy and low-energy diag...A simultaneous high-resolution x-ray backlighting and self-emission imaging method for laser-produced plasma diagnostics is developed in which two Kirkpatrick–Baez imaging channels for high-energy and low-energy diagnostics are constructed using a combination of multilayer mirrors in near-coaxial form.By using a streak or framing camera placed on the image plane,both backlit and self-emission images of a laserproduced plasma with high spatial and temporal resolution can be obtained simultaneously in a single shot.This paper describes the details of the method with regard to its optical and multilayer design,assembly,and alignment method.In addition,x-ray imaging results with a spatial resolution better than 5μm in the laboratory and experimental results with imploding capsules in the SG-III prototype laser facility are presented.展开更多
A bow shock is formed in the interaction of a high-speed laser-driven plasma cloud with a cylinder obstacle. Its temporal and spatial structures are observed by shadowgraphy and interferometry. The width of the shock ...A bow shock is formed in the interaction of a high-speed laser-driven plasma cloud with a cylinder obstacle. Its temporal and spatial structures are observed by shadowgraphy and interferometry. The width of the shock transition region is ～ 50 μm, comparable to the ion–ion collision mean free path, which indicates that collision is dominated in the shock probably. The Mach-number of the ablating plasma cloud is ～ 15 at first, and decreases with time resulting in a changing shock structure. A two-dimension hydrodynamics code, USim, is used to simulate the interaction process. The simulated shocks can well reproduce the observed.展开更多
The Zeeman splitting effect is observed in a strong magnetic field generated by a laser-driven coil.The expanding plasma from the coil wire surface is concentrated at the coil center and interacts with the simultaneou...The Zeeman splitting effect is observed in a strong magnetic field generated by a laser-driven coil.The expanding plasma from the coil wire surface is concentrated at the coil center and interacts with the simultaneously generated magnetic field.The Cu I spectral lines at wavelengths of 510.5541,515.3235,and 521.8202 nm are detected and analyzed.The splittings of spectral lines are used to estimate the magnetic field strength at the coil center as∼31.4±15.7 T at a laser intensity of∼5.6310^(15) W/cm^(2),which agrees well with measurements using a B-dot probe.Some other plasma parameters of the central plasma disk are also studied.The temperature is evaluated from the Cu I spectral line intensity ratio,while the electron density is estimated from the Stark broadening effect.展开更多
We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions....We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions.Ultraviolet-visible absorption spectroscopy and density functional theory calculations were performed to investigate the electronic structure.The experimentally determined direct band gap is 1.39 eV,consistent with the value of the density function theory calculations.Our results reveal that Mg_(3)Si_(2)Te_(6)is a direct gap semiconductor,which is a potential candidate for near-infrared optoelectronic devices.展开更多
Directly driven ablative Rayleigh-Taylor (R-T) instability of modulated CH targets was studied using the face- on X-ray radiography on the Shen-Guang II device. We obtained temporal evolution images of the R-T instabi...Directly driven ablative Rayleigh-Taylor (R-T) instability of modulated CH targets was studied using the face- on X-ray radiography on the Shen-Guang II device. We obtained temporal evolution images of the R-T instability perturbation. The R-T instability growth factor has been obtained by using the methods of fast Fourier transform and seeking the difference of light intensity between the peak and the valley of the targets. Through comparison with the the theoretical simulation, we found that the experimental data had a good agreement with the theoretical simulation results before 1.8 ns, and was lower than the theoretical simulation results after that.展开更多
A 4:1(volume ratio)methanol–ethanol(ME)mixture and silicone oil are two of the most widely used liquid pressure-transmitting media(PTM)in high-pressure studies.Their hydrostatic limits have been extensively studied u...A 4:1(volume ratio)methanol–ethanol(ME)mixture and silicone oil are two of the most widely used liquid pressure-transmitting media(PTM)in high-pressure studies.Their hydrostatic limits have been extensively studied using various methods;however,the evolution of the atomic structures associated with their emerging nonhydrostaticity remains unclear.Here,we monitor their structures as functions of pressure up to∼30 GPa at room temperature using in situ high-pressure synchrotron x-ray diffraction(XRD),optical micro-Raman spectroscopy,and ruby fluorescence spectroscopy in a diamond anvil cell.No crystallization is observed for either PTM.The pressure dependence of the principal diffraction peak position and width indicates the existence of a glass transition in the 4:1MEmixture at∼12 GPa and in the silicone oil at∼3 GPa,beyond which a pressure gradient emerges and grows quickly with pressure.There may be another liquid-to-liquid transition in the 4:1 ME mixture at∼5 GPa and two more glass-to-glass transitions in the silicone oil at∼10 GPa and∼16 GPa.By contrast,Raman signals only show peak weakening and broadening for typical structural disordering,and Raman spectroscopy seems to be less sensitive than XRD in catching these structural transitions related to hydrostaticity variations in both PTM.These results uncover rich pressure-induced transitions in the two PTM and clarify their effects on hydrostaticity with direct structural evidence.The high-pressure XRD and Raman data on the two PTM obtained in this work could also be helpful in distinguishing between signals from samples and those from PTM in future high-pressure experiments.展开更多
Using a combination of static precompression and laser-driven shock compression, shock temperature and reflectivity of H_2O have been measured up to 350 GPa and 2.1×10~4 K. Here, two calibration standards were ap...Using a combination of static precompression and laser-driven shock compression, shock temperature and reflectivity of H_2O have been measured up to 350 GPa and 2.1×10~4 K. Here, two calibration standards were applied to enhance temperature measurement reliability. Additionally, in temperature calculations, the discrepancy in reflectivity between active probe beam wavelength and self-emission wavelength has been taken into account to improve the data's precision.Precompressed water's temperature–pressure data are in very good agreement with our quantum molecular dynamics model,suggesting a superionic conductor of H_2O in the icy planets' deep interior. A sluggish slope gradually approaching Dulong–Petit limit at high temperature was found at a specific heat capacity. Also, high reflectivity and conductivity were observed at the same state. By analyzing the temperature–pressure diagram, reflectivity, conductivity and specific heat comprehensively at conditions simulating the interior of planets in this work, we found that as the pressure rises, a change in ionization appears; it is supposedly attributed to energetics of bond-breaking in the H_2O as it transforms from a bonded molecular fluid to an ionic state. Such molecular dissociation in H_2O is associated with the conducting transition because the dissociated hydrogen atoms contribute to electrical properties.展开更多
We demonstrated a scheme of bandwidth expansion and pulse shape optimized to afford 10 PW laser design via spec-tral shaping,which uses the existing Nd:glass amplifier chain of the SG PW laser.Compared to the amplifie...We demonstrated a scheme of bandwidth expansion and pulse shape optimized to afford 10 PW laser design via spec-tral shaping,which uses the existing Nd:glass amplifier chain of the SG PW laser.Compared to the amplified pulse with a gain-narrowing effect,the required parameters of injected pulse energy,spectral bandwidth,and shape are analyzed,to-gether with their influence on the system B-integral,energy output capability,and temporal intensity contrast.A bandwidth expansion to 7 nm by using LiNbO_(3) birefringent spectral shaping resulted in an output energy of 2 kJ in a proof-of-principle experiment.The results are consistent with the theoretical prediction which suggests that the amplifier chain of SG PW laser is capable of achieving 6 kJ at the bandwidth of 7 nm and the B-integral<π.This will support a 10 PW laser with a compressed pulse energy of 4.8 kJ(efficiency=80%)at 480 fs.展开更多
In this paper, we review the status of the multifunctional experimental platform at the National Laboratory of High Power Laser and Physics(NLHPLP). The platform, including the SG-II laser facility, SG-II 9th beam, SG...In this paper, we review the status of the multifunctional experimental platform at the National Laboratory of High Power Laser and Physics(NLHPLP). The platform, including the SG-II laser facility, SG-II 9th beam, SG-II upgrade(SG-II UP) facility, and SG-II 5 PW facility, is operational and available for interested scientists studying inertial confinement fusion(ICF) and a broad range of high-energy-density physics. These facilities can provide important experimental capabilities by combining different pulse widths of nanosecond, picosecond, and femtosecond scales. In addition, the SG-II UP facility, consisting of a single petawatt system and an eight-beam nanosecond system, is introduced including several laser technologies that have been developed to ensure the performance of the facility. Recent developments of the SG-II 5 PW facility are also presented.展开更多
We present a spatiotemporal model of pulse amplification in the double-pass active mirror(AM)geometry.Three types of overlap condition are studied,and the spatiotemporal scaling under the four-pulse overlapping(4 PO)c...We present a spatiotemporal model of pulse amplification in the double-pass active mirror(AM)geometry.Three types of overlap condition are studied,and the spatiotemporal scaling under the four-pulse overlapping(4 PO)condition is fully characterized for the first time,by mapping the temporal and spatial segments of beam to the instantaneous gain windows.Furthermore,the influence of spatiotemporal overlaps on the amplified energy,pulse distortion and intensity profile is unraveled for both AM and zigzag configurations.The model,verified by excellent agreement between the predicted and measured results,can be a powerful tool for designing and optimizing high energy multi-pass solid-state laser amplifiers with AM,zigzag and other geometries.展开更多
A time-resolved multispectral X-ray imaging approach with new version of multi-channel KirkpatrickBaez(KB) microscope is developed for laser plasma diagnostics at the kilojoule-class Shenguang-II laser facility(SG-II)...A time-resolved multispectral X-ray imaging approach with new version of multi-channel KirkpatrickBaez(KB) microscope is developed for laser plasma diagnostics at the kilojoule-class Shenguang-II laser facility(SG-II). The microscope uses a total external reflection mirror in the sagittal direction and an array of multilayer mirrors in the tangential direction to obtain multiple individual high-resolution, highthroughput, and quasi-monochromatic X-ray images. The time evolution of the imploded target in multiple X-ray energy bands can be acquired when coupled with an X-ray streak camera. The experimental result of the time-resolved 2.5 and 3.0 keV dual-spectral self-emission imaging of the undoped CH shell target on SG-II is given.展开更多
Through the use of time and space integrated kiloelectronvolt (keV) spectroscopy,we investigate the thermal emission of plasma,which produces strong line emission from the titanium K shell (He-α at 4.7 keV and H-α a...Through the use of time and space integrated kiloelectronvolt (keV) spectroscopy,we investigate the thermal emission of plasma,which produces strong line emission from the titanium K shell (He-α at 4.7 keV and H-α at 4.9 keV),created by laser. In order to optimize the conversion efficiency enhancement on titanium foils,the experiment is conducted under a variety of laser-driven intensity conditions. The X-ray emission intensity at 4.7 keV is measured and compared with prediction. The experimental result demonstrates that the solid Ti target laser-produced plasma (LPP) source has X-ray emission at 4.7 keV,which are all generated from electronic transitions in Ti ions at pulse width of 2.1 ns or 30 ps,the crudely evaluated He-α X-ray intensity appears to slightly increase with laser intensity enhancement,and the prepulse effect increases the conversion efficiency of the He-α X-ray. In addition,a 90-μm-thick Ti foil as a filter is used to transmit He-α X-ray at near 4.7 keV,creating a quasi-monochromatic transmission and greatly reducing the lower-and higher-energy background.展开更多
基金supported by the National Science Foundation of China under Award Nos.12074353 and 12075227.
文摘The use of broadband laser technology is a novel approach for inhibiting processes related to laser plasma interactions(LPIs).In this study,several preliminary experiments into broadband-laser-driven LPIs are carried out using a newly established hundreds-of-joules broadband second-harmonic-generation laser facility.Through direct comparison with LPI results for a traditional narrowband laser,the actual LPI-suppression effect of the broadband laser is shown.The broadband laser had a clear suppressive effect on both back-stimulated Raman scattering and back-stimulated Brillouin scattering at laser intensities below 1×10^(15) W cm^(−2).An abnormal hot-electron phenomenon is also investigated,using targets of different thicknesses.
基金National Natural Science Foundation of China(No.11805212)National Key Research and Development Program of China(No.2019YFE03080200)。
文摘Monochromatic x-ray imaging is an essential method for plasma diagnostics related to density information.Large-field high-resolution monochromatic imaging of a He-like iron(Fe XXV)Kαcharacteristic line(6.701 keV)for laser plasma diagnostics was achieved using a developed toroidal crystal x-ray imager.A high-index crystal orientation Ge(531)wafer with a Bragg angle of 75.37°and the toroidal substrate were selected to obtain sufficient diffraction efficiency and compensate for astigmatism under oblique incidence.A precise offline assembly method of the toroidal crystal imager based on energy substitution was proposed,and a spatial resolution of 3-7μm was obtained by toroidal crystal imaging of a 600 line-pairs/inch Au grid within an object field of view larger than 1.0 mm.The toroidal crystal x-ray imager has been successfully tested via side-on backlight imaging experiments of the sinusoidal modulation target and a 1000 line-pairs/inch Au grid with a linewidth of 5μm using an online alignment method based on dual positioning balls to indicate the target and backlighter.This paper describes the optical design,adjustment method,and experimental results of a toroidal crystal system in a laboratory and laser facility.
基金Supported by the Laser Domain of the Chinese National High Technology Plan。
文摘AmpliHcation of spontaneous emissions at 19.6,23.2 and 23.6 nm have been observed by a “ultiple-Target Series Coupling”design in Ge plasma,.The combined length for four targets is up to 56mm.The gain length product(GL)of small signal is up to 18 for both lines at 23.2 and 23.6 nmt and the effective GL is 16.4 and 15.7 for these two lines respectively.This two lines are obviously tending to saturation.The divergence of x-ray laser beam is about 4 mrad.
基金We thank the UCLA-IST OSIRIS Consortium for the use of OSIRIS.This research was supported by Science Challenge Project No.TZ2016005,by the Strategic Priority Research Program of the Chinese Academy of Sciences,Grant Nos.XDA25050400 and XDB16000000the National Natural Science Foundation of China(NSFC)under Grant Nos.11772324 and 11621202the Fundamental Research Funds for the Central Universities.Some of the numerical calculations in this paper were done on the supercomputing system at the Supercomputing Center of the University of Science and Technology of China.
文摘We present particle-in-cell(PIC)simulations of laser plasma instabilities(LPIs)with a laser pulse duration of a few picoseconds.The simulation parameters are appropriate to the planar-target LPI experimental conditions on SG-II.In this regime,the plasmas are characterized by a long electron density scale length and a large electron density range.It is found that when the incident laser intensity is well above its backward stimulated Raman scattering(backward SRS,BSRS)threshold,the backscattered light via the primary BSRS is intense enough to excite secondary SRS(Re-SRS)in the region below one-ninth of the critical density of the incident laser.The daughter light wave via the secondary BSRS(Re-BSRS)is amplified as it propagates toward the higher-density region in the bath of broadband light generated through the primary BSRS process.A higher intensity of the incident laser not only increases the amplitude of the BSRS light but also increases the convective amplification lengths of the Re-BSRS modes by broadening the spectrum of the BSRS light.Convective amplification of Re-BSRS causes pump depletion of the primary BSRS light and may lead to an underestimate of the primary BSRS level in SP-LPI experiments.Asignificant fraction of the generation of energetic electrons is strongly correlated with the Re-BSRS modes and should be considered as a significant energy loss.
基金supported by the National Natural Science Foundation of China(Grant No.11175167)
文摘The X-ray spectrometer used in high-energy-density plasma experiments generally requires both broad X-ray energy coverage and high temporal, spatial, and spectral resolutions for overcoming the difficulties imposed by the X-ray background, debris, and mechanical shocks. By using an elliptical crystal together with a streak camera, we resolve this issue at the SG-II laser facility. The carefully designed elliptical crystal has a broad spectral coverage with high resolution, strong rejection of the diffuse and/or fluorescent background radiation, and negligible source broadening for extended sources.The spectra that are Bragg reflected(23?< θ < 38?) from the crystal are focused onto a streak camera slit 18 mm long and about 80 μm wide, to obtain a time-resolved spectrum. With experimental measurements, we demonstrate that the quartz(1011) elliptical analyzer at the SG-II laser facility has a single-shot spectral range of(4.64–6.45) keV, a typical spectral resolution of E/?E = 560, and an enhanced focusing power in the spectral dimension. For titanium(Ti) data, the lines of interest show a distribution as a function of time and the temporal variations of the He-α and Li-like Ti satellite lines and their spatial profiles show intensity peak red shifts. The spectrometer sensitivity is illustrated with a temporal resolution of better than 25 ps, which satisfies the near-term requirements of high-energy-density physics experiments.
基金supported by the National High Technology Development Program of China (Grant No. 2009AA8046006)
文摘Several experiments are performed on the ShenGuang-II laser facility to investigate an x-ray source and test radiography concepts.X-ray lines emitted from laser-produced plasmas are the most practical means of generating these high intensity sources.By using a time-integrated space-resolved keV spectroscope and pinhole camera,potential helium-like titanium Kα x-ray backlighting (radiography) line source is studied as a function of laser wavelength,ratio of pre-pulse intensity to main pulse intensity,and laser intensity (from 7.25 to～11.3×10 15 W/cm 2).One-dimensional radiography using a grid consisting of 5 μm Au wires on 16 μm period and the pinhole-assisted point projection is tested.The measurements show that the size of the helium-like titanium Kα source from a simple foil target is larger than 100 μm,and relative x-ray line emission conversion efficiency ξ x from the incident laser light energy to heliumlike titanium K-shell spectrum increases significantly with pre-pulse intensity increasing,increases rapidly with laser wavelength decreasing,and increases moderately with main laser intensity increasing.It is also found that a gold gird foils can reach an imaging resolution better than 5-μm featured with high contrast.It is further demonstrated that the pinhole-assisted point projection at such a level will be a novel two-dimensional imaging diagnostic technique for inertial confinement fusion experiments.
文摘The use of low-coherence light is expected to be one of the effective ways to suppress or even eliminate the laser–plasma instabilities that arise in attempts to achieve inertial confinement fusion.In this paper,a review of low-coherence high-power laser drivers and related key techniques is first presented.Work at typical low-coherence laser facilities,including Gekko XII,PHEBUS,Pharos III,and Kanal-2 is described.The many key techniques that are used in the research and development of low-coherence laser drivers are described and analyzed,including low-coherence source generation,amplification,harmonic conversion,and beam smoothing of low-coherence light.Then,recent progress achieved by our group in research on a broadband low-coherence laser driver is presented.During the development of our low-coherence high-power laser facility,we have proposed and implemented many key techniques for working with low-coherence light,including source generation,efficient amplification and propagation,harmonic conversion,beam smoothing,and precise beam control.Based on a series of technological breakthroughs,a kilojoule low-coherence laser driver named Kunwu with a coherence time of only 300 fs has been built,and the first round of physical experiments has been completed.This high-power laser facility provides not only a demonstration and verification platform for key techniques and system integration of a low-coherence laser driver,but also a new type of experimental platform for research into,for example,high-energy-density physics and,in particular,laser–plasma interactions.
文摘An experiment with thin titanium foils irradiated by two pulses delayed in time is conducted on the Shenguang-II laser facility.A prepulse induces an underdense plasma,2-ns later a main pulse(λ L = 0.35 μm,E L ≈ 120 J,τ L ≈ 100 ps) is injected into the underdense plasma and produces strong line emission from the titanium K shell(i.e.,He α at 4.7 keV).Data show that the intensity of 4.7-keV X-ray emission with the prepulse is approximately twice more than without the prepulse,and can be used as a backlighting source satisfying the diagnostic requirements for dense plasma probing.Highquality plasma images are obtained with the backlighting 4.7-keV X-rays in a Rayleigh-Taylor hydrodynamic instability experiment.
基金supported by National MCF Energy R&D Program(Grant No.2019YFE03080200)the National Natural Science Foundation of China(Grant No.11805212)the Fundamental Research Funds for the Central Universities(Grant No.22120200405).
文摘A simultaneous high-resolution x-ray backlighting and self-emission imaging method for laser-produced plasma diagnostics is developed in which two Kirkpatrick–Baez imaging channels for high-energy and low-energy diagnostics are constructed using a combination of multilayer mirrors in near-coaxial form.By using a streak or framing camera placed on the image plane,both backlit and self-emission images of a laserproduced plasma with high spatial and temporal resolution can be obtained simultaneously in a single shot.This paper describes the details of the method with regard to its optical and multilayer design,assembly,and alignment method.In addition,x-ray imaging results with a spatial resolution better than 5μm in the laboratory and experimental results with imploding capsules in the SG-III prototype laser facility are presented.
基金Project supported by the National Basic Research Program of China(Grant No.2013CBA01501)the National Natural Science Foundation of China(Grant Nos.11135012,11375262,11503041,and 11520101003)the Science Challenge Program of China(Grant No.JCKY2016212A505)
文摘A bow shock is formed in the interaction of a high-speed laser-driven plasma cloud with a cylinder obstacle. Its temporal and spatial structures are observed by shadowgraphy and interferometry. The width of the shock transition region is ～ 50 μm, comparable to the ion–ion collision mean free path, which indicates that collision is dominated in the shock probably. The Mach-number of the ablating plasma cloud is ～ 15 at first, and decreases with time resulting in a changing shock structure. A two-dimension hydrodynamics code, USim, is used to simulate the interaction process. The simulated shocks can well reproduce the observed.
基金This work was supported in part by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDA25010100,XDA25010300,and XDA25030100)the National Natural Science Foundation of China(Grant Nos.U1930107 and 11827807)the Japanese Ministry of Education,Science,Sports,and Culture through Grants-in-Aid,KAKENHI(Grant No.21H04454).
文摘The Zeeman splitting effect is observed in a strong magnetic field generated by a laser-driven coil.The expanding plasma from the coil wire surface is concentrated at the coil center and interacts with the simultaneously generated magnetic field.The Cu I spectral lines at wavelengths of 510.5541,515.3235,and 521.8202 nm are detected and analyzed.The splittings of spectral lines are used to estimate the magnetic field strength at the coil center as∼31.4±15.7 T at a laser intensity of∼5.6310^(15) W/cm^(2),which agrees well with measurements using a B-dot probe.Some other plasma parameters of the central plasma disk are also studied.The temperature is evaluated from the Cu I spectral line intensity ratio,while the electron density is estimated from the Stark broadening effect.
基金the National Natural Science Foundation of China(Grant Nos.12174454,11904414,11904416,and 12104427)the Guangdong Basic and Applied Basic Research Foundation,China(Grant No.2021B1515120015)+1 种基金the Guangzhou Basic and Applied Basic Research Foundation(Grant No.202201011123)the National Key Research and Development Program of China(Grant No.2019YFA0705702).
文摘We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions.Ultraviolet-visible absorption spectroscopy and density functional theory calculations were performed to investigate the electronic structure.The experimentally determined direct band gap is 1.39 eV,consistent with the value of the density function theory calculations.Our results reveal that Mg_(3)Si_(2)Te_(6)is a direct gap semiconductor,which is a potential candidate for near-infrared optoelectronic devices.
文摘Directly driven ablative Rayleigh-Taylor (R-T) instability of modulated CH targets was studied using the face- on X-ray radiography on the Shen-Guang II device. We obtained temporal evolution images of the R-T instability perturbation. The R-T instability growth factor has been obtained by using the methods of fast Fourier transform and seeking the difference of light intensity between the peak and the valley of the targets. Through comparison with the the theoretical simulation, we found that the experimental data had a good agreement with the theoretical simulation results before 1.8 ns, and was lower than the theoretical simulation results after that.
基金supported by the National Natural Science Foundation of China(Grant Nos.51871054 and U1930401)The XRD experiments were performed on beamline 15U1 of the Shanghai Synchrotron Radiation Facility(SSRF)and on beamline 13 ID-D of GSECARS at the Advanced Photon Source(APS),Argonne National Laboratory(ANL),USA+2 种基金The use of beamline 13-ID-D at the APS was supported by the National Science Foundation(NSF)–Earth Sciences(Grant No.EAR-1634415)the Department of Energy(DOE)–GeoSciences(GrantNo.DEFG02-94ER14466)supported by the DOE Office of Science(Grant No.DE-AC02-06CH11357).
文摘A 4:1(volume ratio)methanol–ethanol(ME)mixture and silicone oil are two of the most widely used liquid pressure-transmitting media(PTM)in high-pressure studies.Their hydrostatic limits have been extensively studied using various methods;however,the evolution of the atomic structures associated with their emerging nonhydrostaticity remains unclear.Here,we monitor their structures as functions of pressure up to∼30 GPa at room temperature using in situ high-pressure synchrotron x-ray diffraction(XRD),optical micro-Raman spectroscopy,and ruby fluorescence spectroscopy in a diamond anvil cell.No crystallization is observed for either PTM.The pressure dependence of the principal diffraction peak position and width indicates the existence of a glass transition in the 4:1MEmixture at∼12 GPa and in the silicone oil at∼3 GPa,beyond which a pressure gradient emerges and grows quickly with pressure.There may be another liquid-to-liquid transition in the 4:1 ME mixture at∼5 GPa and two more glass-to-glass transitions in the silicone oil at∼10 GPa and∼16 GPa.By contrast,Raman signals only show peak weakening and broadening for typical structural disordering,and Raman spectroscopy seems to be less sensitive than XRD in catching these structural transitions related to hydrostaticity variations in both PTM.These results uncover rich pressure-induced transitions in the two PTM and clarify their effects on hydrostaticity with direct structural evidence.The high-pressure XRD and Raman data on the two PTM obtained in this work could also be helpful in distinguishing between signals from samples and those from PTM in future high-pressure experiments.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0403200)the Science Challenge Project(Grant No.TZ2016001)
文摘Using a combination of static precompression and laser-driven shock compression, shock temperature and reflectivity of H_2O have been measured up to 350 GPa and 2.1×10~4 K. Here, two calibration standards were applied to enhance temperature measurement reliability. Additionally, in temperature calculations, the discrepancy in reflectivity between active probe beam wavelength and self-emission wavelength has been taken into account to improve the data's precision.Precompressed water's temperature–pressure data are in very good agreement with our quantum molecular dynamics model,suggesting a superionic conductor of H_2O in the icy planets' deep interior. A sluggish slope gradually approaching Dulong–Petit limit at high temperature was found at a specific heat capacity. Also, high reflectivity and conductivity were observed at the same state. By analyzing the temperature–pressure diagram, reflectivity, conductivity and specific heat comprehensively at conditions simulating the interior of planets in this work, we found that as the pressure rises, a change in ionization appears; it is supposedly attributed to energetics of bond-breaking in the H_2O as it transforms from a bonded molecular fluid to an ionic state. Such molecular dissociation in H_2O is associated with the conducting transition because the dissociated hydrogen atoms contribute to electrical properties.
基金Projectsupported by the International Partnership Program of Chinese Academy of Sciences(Grant No.181231KYSB20170022)the Natural Science Foundation of Jiangsu Higher Education Institutions of China(Grant No.20KJB140020).
文摘We demonstrated a scheme of bandwidth expansion and pulse shape optimized to afford 10 PW laser design via spec-tral shaping,which uses the existing Nd:glass amplifier chain of the SG PW laser.Compared to the amplified pulse with a gain-narrowing effect,the required parameters of injected pulse energy,spectral bandwidth,and shape are analyzed,to-gether with their influence on the system B-integral,energy output capability,and temporal intensity contrast.A bandwidth expansion to 7 nm by using LiNbO_(3) birefringent spectral shaping resulted in an output energy of 2 kJ in a proof-of-principle experiment.The results are consistent with the theoretical prediction which suggests that the amplifier chain of SG PW laser is capable of achieving 6 kJ at the bandwidth of 7 nm and the B-integral<π.This will support a 10 PW laser with a compressed pulse energy of 4.8 kJ(efficiency=80%)at 480 fs.
基金supported by International Partnership Program of Chinese Academy of Sciences(No.181231KYSB20170022)the Key Projects of International Cooperation in Chinese Academy of Sciences
文摘In this paper, we review the status of the multifunctional experimental platform at the National Laboratory of High Power Laser and Physics(NLHPLP). The platform, including the SG-II laser facility, SG-II 9th beam, SG-II upgrade(SG-II UP) facility, and SG-II 5 PW facility, is operational and available for interested scientists studying inertial confinement fusion(ICF) and a broad range of high-energy-density physics. These facilities can provide important experimental capabilities by combining different pulse widths of nanosecond, picosecond, and femtosecond scales. In addition, the SG-II UP facility, consisting of a single petawatt system and an eight-beam nanosecond system, is introduced including several laser technologies that have been developed to ensure the performance of the facility. Recent developments of the SG-II 5 PW facility are also presented.
基金National Key Research and Development Program of China(No.2017YFB0405100)National Natural Science Foundation of China(No.61975087)Beijing Young Talents Support Project(No.2017000020124G044)。
文摘We present a spatiotemporal model of pulse amplification in the double-pass active mirror(AM)geometry.Three types of overlap condition are studied,and the spatiotemporal scaling under the four-pulse overlapping(4 PO)condition is fully characterized for the first time,by mapping the temporal and spatial segments of beam to the instantaneous gain windows.Furthermore,the influence of spatiotemporal overlaps on the amplified energy,pulse distortion and intensity profile is unraveled for both AM and zigzag configurations.The model,verified by excellent agreement between the predicted and measured results,can be a powerful tool for designing and optimizing high energy multi-pass solid-state laser amplifiers with AM,zigzag and other geometries.
基金the National Natural Science Foundation of China(Nos.11305116 and 11105098)the National Key Technology Support Program(No.2013BAK14B02)the National"973"Program ofChina(No.2011CB922203)
文摘A time-resolved multispectral X-ray imaging approach with new version of multi-channel KirkpatrickBaez(KB) microscope is developed for laser plasma diagnostics at the kilojoule-class Shenguang-II laser facility(SG-II). The microscope uses a total external reflection mirror in the sagittal direction and an array of multilayer mirrors in the tangential direction to obtain multiple individual high-resolution, highthroughput, and quasi-monochromatic X-ray images. The time evolution of the imploded target in multiple X-ray energy bands can be acquired when coupled with an X-ray streak camera. The experimental result of the time-resolved 2.5 and 3.0 keV dual-spectral self-emission imaging of the undoped CH shell target on SG-II is given.
基金supported by the National "863" Program of China under Grant No. 2006AA804312
文摘Through the use of time and space integrated kiloelectronvolt (keV) spectroscopy,we investigate the thermal emission of plasma,which produces strong line emission from the titanium K shell (He-α at 4.7 keV and H-α at 4.9 keV),created by laser. In order to optimize the conversion efficiency enhancement on titanium foils,the experiment is conducted under a variety of laser-driven intensity conditions. The X-ray emission intensity at 4.7 keV is measured and compared with prediction. The experimental result demonstrates that the solid Ti target laser-produced plasma (LPP) source has X-ray emission at 4.7 keV,which are all generated from electronic transitions in Ti ions at pulse width of 2.1 ns or 30 ps,the crudely evaluated He-α X-ray intensity appears to slightly increase with laser intensity enhancement,and the prepulse effect increases the conversion efficiency of the He-α X-ray. In addition,a 90-μm-thick Ti foil as a filter is used to transmit He-α X-ray at near 4.7 keV,creating a quasi-monochromatic transmission and greatly reducing the lower-and higher-energy background.
