Rapid Plasma Expansion Research Articles

Controllable preparation of black phosphorus nanomaterials via liquid-phase pulsed discharge

The N, N-dimethylformamide (DMF) organic solvent was deliberately chosen as the optimal medium for this investigation. To achieve uniform dispersion of black phosphorus powder, which was obtained via shock-induced phase transformation, it was effectively dispersed in the DMF solution, resulting in a homogeneous black phosphorus-DMF suspension. Subsequently, a liquid-phase pulsed discharge experiment was conducted. This experimental setup harnessed the shockwave and tensile stripping effects generated by the rapid expansion of plasma during the liquid-phase pulsed discharge. These phenomena facilitated the interlayer exfoliation and dispersion of black phosphorus molecules, ultimately leading to the formation of a suspension containing black phosphorus quantum dots. In-depth investigation into the formation mechanism of black phosphorus quantum dots was also undertaken. Our findings reveal a pivotal influence of the charging voltage on the microstructure of the recovered samples. Specifically, as the charging voltage increases, the lateral dimensions of the retrieved two-dimensional black phosphorus powder undergo a remarkable reduction, transitioning from the micron-scale to less than 10 nm. The above results, which stem from meticulous experimentation and analysis, emphasize the significance of controlled synthesis in producing black phosphorus quantum dots with varying microstructures. Such insights hold substantial promise for advancing the field of materials science and enhancing the applicability of black phosphorus quantum dots in diverse applications.

Emission of electromagnetic waves as a stopping mechanism for nonlinear collisionless ionization waves in a high-β regime.

A high energy density plasma embedded in a neutral gas is able to launch an outward-propagating nonlinear electrostatic ionization wave that traps energetic electrons. The trapping maintains a strong sheath electric field, enabling rapid and long-lasting wave propagation aided by field ionization. Using 1D3V kinetic simulations, we examine the propagation of the ionization wave in the presence of a transverse MG-level magnetic field with the objective to identify qualitative changes in a regime where the initial thermal pressure of the plasma exceeds the pressure of the magnetic field (β>1). Our key finding is that the magnetic field stops the propagation by causing the energetic electrons sustaining the wave to lose their energy by emitting an electromagnetic wave. The emission is accompanied by the magnetic field expulsion from the plasma and an increased electron loss from the trapping wave structure. The described effect provides a mechanism mitigating rapid plasma expansion for those applications that involve an embedded plasma, such as high-flux neutron production from laser-irradiated deuterium gas jets.

A statistical approach to controlling the size of aluminum nanoparticles synthesized by pulsed laser ablation in liquid

In this study, pulsed laser ablation in liquid (PLAL) was performed to synthesize nanoparticles by irradiating a laser to a target material in a specific solvent. The effect of laser parameters on the size and deviation of nanoparticles was quantitatively analyzed using the design of experiments. The increased laser energy induced rapid plasma expansion, reducing the size of the synthesized nanoparticles. However, when the laser energy exceeds a critical value, the ablation rate was reduced because the primary synthesized nanoparticles absorb the subsequent laser energy. When the laser beam diameter increased, the probability that the vapor atoms or ions collide with each other increased, but the change in the final particle size was minimal because most of the generated particles were fragmented by exposure to subsequent laser beams. The size deviation of the nanoparticles produced by PLAL decreased with increasing laser energy and increasing beam diameter as the effect of the subsequent laser beam became prominent under this process condition. A methodology for determining the process conditions for producing aluminum (Al) nanoparticles with the desired size and minimum deviation was proposed and validated through analysis of variance (ANOVA) and simple mathematical modeling.

Double-pulse laser synchronization aimed at simultaneous detection of enhanced atomic and molecular signals at low pressure conditions

A double pulse laser system that combines Raman spectroscopy and laser induced plasma spectroscopy (LIPS) in a single unit is demonstrated. The study attempts to improve the atomic signals of LIPS while simultaneously extracting the desired molecular signals from Raman. In low pressure conditions such as the lunar atmosphere, the detection of plasma emission is difficult due to the low electron density and short persistence time causing a rapid plasma expansion. Moreover, in the integration of the spectroscopic system aimed at space exploration, the system size and weight should be minimized. Simultaneous molecular and atomic detection that gave highly resolved spectra of both LIPS and Raman at pressure below 0.07 Torr is achieved. First, a low-energy laser pulse was used to produce a small plasma and to detect the molecular signals through the inelastic scattering effect. Then, the laser pulse at a higher energy is used to produce a larger plasma plume for detecting the atomic signals. Amongst eight rock samples tested, plasma stacking by generating two sequential plasmas produced from the double-pulse laser on Calcite for example enhanced the signal intensities of calcium and oxygen lines by twofold, compared to a conventional LIPS.

Cavitation bubble nucleation induced by shock-bubble interaction in a gelatin gel

An optical visualization technique is developed to study cavitation bubble nucleation that results from interaction between a laser-induced shock and a preexisting gas bubble in a 10 wt. % gelatin gel; images of the nucleated cavitation bubbles are captured and the cavitation inception pressure is determined based on Euler flow simulation. A spherical gas cavity is generated by focusing an infrared laser pulse into a gas-supersaturated gel and the size of the laser-generated bubble in mechanical equilibrium is tuned via mass transfer of the dissolved gas into the bubble. A spherical shock is then generated, through rapid expansion of plasma induced by the laser focusing, in the vicinity of the gas bubble. The shock-bubble interaction is recorded by a CCD camera with flash illumination of a nanosecond green laser pulse. The observation captures cavitation inception in the gel under tension that results from acoustic impedance mismatching at the bubble interface interacting with the shock. We measure the probability of cavitation inception from a series of the repeated experiments, by varying the bubble radius and the standoff distance. The threshold pressure is defined at the cavitation inception probability equal to one half and is calculated, through comparisons to Euler flow simulation, at −24.4 MPa. This threshold value is similar to that from shock-bubble interaction experiments using water, meaning that viscoelasticity of the 10 wt. % gelatin gel has a limited impact on bubble nucleation dynamics.

衝撃波と気泡の干渉によるゼラチンゲルのキャビテーション初生

We experimentally and numerically study a shock-bubble interaction problem in gelatin gels. The nucleation of spherical gas bubbles is triggered by focusing an infrared laser pulse into gassupersaturated gels and the radius of the nucleated bubble is controlled by mass transfer of the dissolved gases. A spherical shock is then generated, through rapid expansion of plasma induced by the laser focusing, in the vicinity of the gas bubble. The shock-bubble interaction is recorded by a CCD camera with flash illumination of a nanosecond green laser pulse. The observation captures cavitation inception in the gelatin under tension that results from acoustic impedance mismatching at the bubble wall. We measure the probability of cavitation with varying the bubble radius and the standoff distance. The threshold pressure for the cavitation inception is defined by the probability equal to one half and is predicted, through comparisons to Euler flow simulations, at −25 MPa.

Cloud cavitation induced by shock-bubble interaction in a viscoelastic solid

We experimentally study a shock-bubble interaction problem in a viscoelastic solid, which is relevant to shock wave lithotripsy. A gas bubble is produced by focusing an infrared laser pulse into gelatin. A spherical shock is then created, through rapid expansion of plasma that results from the laser focusing, in the vicinity of the gas bubble. The shock-bubble interaction is recorded by a CCD camera with flash illumination of a nanosecond green laser pulse. The observation captures cavitation inception in the gelatin under tension that results from acoustic impedance mismatching at the bubble wall. Namely, the shock reflects at the bubble interface as a rarefaction wave, which induces the nucleation of cavitation bubbles as a result of rupturing the gelatin.

Guiding of intense laser beams in highly ionized plasma columns generated by a fast capillary discharge.

We have demonstrated the guiding of laser pulses with peak intensities up to 2.2 x 10(17) W/cm(2) in a 5.5 cm long plasma column containing highly charged Ar ions generated by a fast capillary discharge. A rapid discharge-driven hydrodynamic compression guides progressively lower order modes through a plasma with increasing density and degree of ionization, until the guide collapses on axis. The lowest order mode (FWHM approximately 50 microm) is guided with 75% transmission efficiency shortly before the plasma reaches the conditions for lasing in Ne-like Ar. The subsequent rapid plasma expansion forms a significantly leakier and more absorbent guide.

Cathode and anode plasmas in short-pulse explosive field emission cathodes

Explosive field emission cathodes have been a subject of research for a number of years. These cathodes offer high current densities and total current without requiring a heater for the production of electrons. Generally these cathodes consist of some structure with a series of tips or metal–dielectric regions in which a large electric field enhancement can occur. A cathode plasma is then formed from these discharge points that then supplies the electrons necessary for space charge limited emission. This article reports on a series of optical measurements in which the cathode and anode plasmas of explosive field emission cathodes are observed. Three types of cathodes are investigated. These types are a polymer velvet cathode, a metal–dielectric cathode, and a tufted carbon fiber cathode in which the fibers have been coated with a cesium iodide salt. Cesium iodide coated carbon fiber cathodes have shown a great deal of promise for various field emitter applications. From these high speed photos, the evolution of the plasmas on both cathode and anode can be qualitatively ascertained. Experimentally we find that not only does cathode plasma behavior depend on the type of cathode, but the anode plasma behavior does also. Further, we find that the best performing cathode shows the most rapid plasma formation on both anode and cathode, yet without a rapid plasma expansion across the anode–cathode gap.

The role of albumin in nutritional support.

Hypoalbuminemia is considered one of the hallmarks of protein-calorie malnutrition and chronic liver disease. Recently, serum albumin has also been proposed as a critical predictor of the response to nutritional support and tolerance to enteral feeding in critically ill patients. Albumin is essential for maintenance of plasma colloidal osmotic pressure, prevention of edema, and transport of certain drugs and nutrients. Experimental studies have shown that rapid plasma expansion and reduced plasma protein concentration and osmotic pressure induce a net secretion of sodium and water into the small intestinal lumen. However, the effects of chronic hypoalbuminemia per se on intestinal absorption, independent of malnutrition, have not been fully studied. It is documented that both chronic illness and malnutrition may profoundly affect intestinal anatomical structure and function, inducing some degree of malabsorption. In the last few years, some have advocated albumin infusion to improve clinical response to patients with hypoalbuminemia receiving parenteral nutritional support or to reduce intestinal intolerance and diarrhea in patients receiving enteral tube feeding. A review of the literature shows that both clinical and experimental data to support these suggestions are scarce and further investigations are needed. Hypoalbuminemia is one of many parameters of malnutrition, and it is unlikely that correction of a single parameter for a short time would lead to major clinical benefits.

Photogenerated high-density electron-hole plasma energy relaxation and experimental evidence for rapid expansion of the electron-hole plasma in CdSe.

The kinetics of the nonequilibrium photogenerated electron-hole plasma in CdSe is investigated using picosecond time-resolved spectroscopy at room temperature. Based on the fact that the polar optical-phonon emission rate is reduced due to screening by the high density of the e-h plasma, the remaining dominant mechanism for hot-carrier cooling is the nonpolar optical-phonon emission even though CdSe is a highly polar semiconductor. It has been observed that the photogenerated carrier density is much lower than the estimated carrier density using known values of the absorption coefficient, reflectivity, and photon fluence. Rapid plasma expansion has been proposed as a possible explanation on the grounds of the observed larger spatial width of the photoluminescence relative to the laser spatial width, moderate change of Auger recombination rate with the excitation fluence, the absence of an observed change in the Fermi level with increased excitation intensity, and earlier formation of excitons after the picosecond pulse (5 psec) excitation at a low temperature (12 K). The observed carrier density \ensuremath{\approxeq}35 psec after excitation is limited to 1\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ within the excitation photon fluence of 2\ifmmode\times\else\texttimes\fi{}${10}^{15}$\char21{}7\ifmmode\times\else\texttimes\fi{}${10}^{16}$ photons/${\mathrm{cm}}^{2}$ at room temperature. Large values of the diffusion constant are explained in terms of a screened electron-phonon interaction. The possibility of saturation of the available states in explaining small carrier densities is eliminated by the observed faster cooling rate at low-excitation intensity and the sublinear change in the luminescence spatial width with excitation fluence.

Re-thermalisation and flow of laser-produced plasmas in a uniform magnetic field

Detailed time- and spatially-resolved measurements of the electron temperature and plasma density have been made, by means of laser Thomson scattering and other plasma diagnostics, for plasmas produced by laser from a thin wire target in an almost uniform magnetic field ( approximately 1 T). The physical processes involved in plasma/magnetic-field interactions are discussed. It has been found that a part of the translational kinetic energy of the ions in an earlier rapid plasma expansion phase is reconverted into the thermal energy of electrons as the results of the interactions, through the ohmic heating, by a circulating diamagnetic current flowing near the plasma outer boundary, as well as through subsequently shock heating (and additional compression). Also, the plasma expansion along magnetic field lines may be regarded as almost one-dimensional, and the time variation of electron temperature is adiabatic.

Site of Accumulation of Red Blood Cells and Plasma During Rapid Plasma Expansion

Site of Accumulation of Red Blood Cells and Plasma During Rapid Plasma Expansion