arXiv subjects

Mikhail N. Shneider

Publications and source records attributed to Mikhail N. Shneider.

At least 19 recordsLinked to original sources

arXiv2026

Non-resonant laser-driven narrowing of particle velocity distributions

Stark acceleration and deceleration based techniques for generating particle ensembles with low velocity spread are useful in many experimental applications. For a given velocity distribution of a particle ensemble, these techniques accelerate or decelerate a small subset of the total population, with a low velocity uncertainty. However, narrowing the original velocity distribution by accelerating or decelerating the ensemble particles near the mean velocity is fundamentally limited and not yet explored. We present a numerical study of particle dynamics using neutral cesium atoms as an example. We investigate different interaction regimes, identify key limitations, and propose an interaction regime in which optical Stark deceleration can be used to narrow the velocity distribution of a propagating ensemble about its mean velocity. These findings have potential implications for optical manipulation and control, controlled collisions, and matter interferometry.

physics.optics↗

arXiv2026

Spark-Induced Shockwave Dynamics Revealed via Nonresonant Four-Wave Mixing

We report on the experimental detection of shockwave dynamics produced in a spark discharge, using a nonresonant four-wave mixing optical technique. In particular, we observe the spark-induced local density perturbation across a millimeter-range probe volume, centered on the discharge, via single-shot coherent Rayleigh-Brillouin scattering. We detect the emergence of shock-induced flow velocities, which appear as distinct features in the spectrum, and monitor their dynamic evolution from a few hundred nanoseconds to microseconds after the spark. Finally, we benchmark our measurements against simulations based on a one-dimensional compressible flow model. Our results pave the way for quantitative measurements of highly non-uniform transient flows in challenging environments featuring non-equilibrium gas kinetics.

physics.optics↗

arXiv2025

Decomposition of Methane Diluted with Inert Gas in an RF Discharge Cell

Decomposition of methane using non-thermal plasmas is an attractive route for producing hydrogen-rich gases and valuable carbon nanomaterials. Understanding how plasma discharge modes influence methane decomposition in optimizing plasma-assisted chemical conversion remains unexplored. This study explores the coupling between the discharge structure and product selectivity in RF capacitively coupled discharges operating in methane/inert gas mixtures in the pressure range of 2 to 3 torr. The discharge exhibits mode transitions from uniform to striated in Ar and Kr and from diffuse to contracted in Ar and Kr with 5 percent or less CH4. The discharges in He and Ne remained uniform under our operating conditions, and their mixtures with CH4 remained diffuse. A 0-D model for Ar/CH4 discharge established a threshold for contraction while also asserting the importance of Ar metastable in the dissociation and ionization processes. The highest degree of methane decomposition, 99.7% with the main products of acetylene and graphitized solid carbon was achieved in the contracted discharge mode for both Kr or Ar with 5% or less CH4. We demonstrate that contraction can play a crucial role in the effective decomposition of methane with value-added products and that both the electronic and thermal properties of plasma gas are responsible for this effect.

physics.plasm-ph↗

arXiv2025

Sub-barrier cavitation in liquid helium

In this paper, the tunneling mechanism of cavitation in liquid helium for 3He and 4He is considered on the basis of the Schrödinger-like equation. It is assumed that the pairwise interactions of helium atoms are determined by the Lennard-Jones potential. The kinetics of nucleation and the mechanism that limits the growth of cavitation bubbles in liquid helium are considered, taking into account their growth in a negative pressure field.

cond-mat.soft↗

arXiv2025

Frequency modulation of THz emission from a laser filament array

A simple traveling wave antenna model is used to theoretically study emission from an array of filaments. Both transverse and longitudinal arrays of filaments are considered. The angular distribution and power in the THz signal are significantly modified, which is consistent with other trends reported in the literature. The frequency content of the THz emission signal is also strongly modified under certain conditions. Whereas the emission from a single filament is broadband, the emission from a periodic transverse array consists of several discrete frequencies. For this latter case, the THz spectrum can be approximated as the product of two factors - the spectrum from a single filament and a complex frequency-dependent phase factor associated with the spatial distribution of the filaments. The complex phase factor accounts for interference effects, amplifying certain frequencies from the single filament spectrum while suppressing others. The location and width of the discrete frequencies present in the final spectrum depends on the number of filaments and their spacing. These results point to an interesting possibility of tailoring the frequency content in the THz signal.

physics.plasm-ph↗

arXiv2025

Axisymmetric model for 1-color laser filament THz emission

A 3D axisymmetric model for laser beam propagation in air is proposed for use with THz emission calculations. The model accounts for nonlinear propagation of the femtosecond pulse that generates the filament (Kerr self-focusing and plasma defocusing). The formalism proposed can be applied across a broad range of experimental parameters - focal lengths, beam profiles, and intensities. We adapt existing models of 1-color THz emission for use with the beam propagation model to calculate THz emission signatures. Two of these THz emission models are used - a 1D model and a more detailed 3D axisymmetric model. For the test case considered, nonlinear propagation dynamics have a large impact on the amplitude of the THz signal, but only a minimal impact on the frequency content and angular distribution of the signal.

physics.plasm-ph↗

arXiv2024

One-dimensional mapping of femtosecond laser filaments using coherent microwave scattering

This paper reports on the use of coherent microwave scattering (CMS) for spatially resolved electron number density measurements of elongated plasma structures induced at mid-IR femtosecond filamentation in air. The presented studies comprise one-dimensional mapping of laser filaments induced via 3.9 um, 127.3 fs laser pulses at output energies up to 15 mJ. The axial electron number density was measured to be invariant (about 2x10$^{15}$ cm$^{-3}$) along the entire filament length and for all tested laser pulse energies 5-15 mJ, and the corresponding laser intensity in the middle portion of the filament was estimated to be nearly constant for 5-15 mJ pulse energies (about 30-40 TW/cm$^2$). These fundings support that intensity clamping conditions were achieved in the experiments. The proposed approach enables capabilities that are currently unavailable to perform absolute and longitudinally resolved measurements of electron number density in laser filaments and to precisely characterize conditions associated with self-focusing and intensity clamping.

physics.plasm-ph↗

arXiv2024

Experimental study of cavitation development in liquid in pulsed non-uniform electric field under the action of ponderomotive forces

In this paper, the Rayleigh scattering method is used to study the formation of cavitation in water in a pulsed inhomogeneous electric field when a nanosecond high voltage pulse is applied to a needle-like electrode. The observational results confirm the theoretical picture of cavitation development under the action of electrostrictive ponderomotive forces. The values of the negative pressure, the average size of the cavitation nanovoids and their concentration were obtained from these measurements, which are in agreement with theoretical estimates.

physics.flu-dyn↗

arXiv2022

Ionization rate and plasma dynamics at 3.9 micron femtosecond photoionization of air

The introduction of mid-IR optical parametric chirped pulse amplifiers (OPCPAs) has catalyzed interest in multi-millijoule, infrared femtosecond pulse-based filamentation. As tunneling ionization is a fundamental first stage in these high-intensity laser-matter interactions, characterizing the process is critical to understand derivative topical studies on femtosecond filamentation and self-focusing. Here, we report constructive-elastic microwave scattering-based measurements of total electron count, electron number densities, and photoionization rates generated by 3.9 micron femtosecond mid-infrared tunneling ionization of atmospheric air. Consequently, we determine photoionization rates in the range of 5.0x10$^{8}$-6.1x10$^{9}$ s$^{-1}$ for radiation intensities 1.3x10$^{13}$-1.9x10$^{14}$ W/cm$^{2}$, respectively. The proposed approach paves the wave to precisely tabulate photoionization rates in mid-IR for broad range of intensities and gas types and to study plasma dynamics at mid-IR filamentation.

physics.plasm-ph↗

arXiv2022

Effects of plasma on physical properties of water: nanocrystalline-to-amorphous phase transition and improving produce washing

Recently is was discovered in various applications that many physical and chemical properties of water change their temperature dependence between about 35 and 60 degrees Celsius. In particular, heat conductance, light absorption, and surface tension all change their temperature dependence. These drastic changes were associated with water gradually changing its mesoscopic structure: while at the higher temperatures water is a uniform media (amorphous state), at the temperatures below transition it consists of many nano-to-micro-scale clusters (crystalline state). This transition is similar to the second order phase transition. In the present paper we show that treating water with non-thermal plasma (adding plasma-created active compounds) can lower the temperature of the transition and thus cause a significant change in such physical quantities as surface tension, viscosity, freezing rate, and wettability and washability. We present analytical estimates of the transition temperature shift based on the Debya-Huckel theory. We discuss the produce-washing experiments that illustrate the predicted effects.

physics.plasm-ph↗

arXiv2021

Theoretical model of external spinal cord stimulation

In this paper, a simple theoretical model of excitation of action potentials of multiple motor pools by stimulating current pulses over the lumbosacral regions of the spinal cord is presented. The present model is consistent with known experimental data.

physics.med-ph↗

arXiv2021

Thomson and Collisional Regimes of In-Phase Coherent Microwave Scattering Off Gaseous Microplasmas

The total number of electrons in a classical microplasma can be non-intrusively measured through elastic in-phase coherent microwave scattering (CMS). Here, we establish a theoretical basis for the CMS diagnostic technique with an emphasis on Thomson and collisional scattering in short, thin unmagnetized plasma media. Experimental validation of the diagnostic is subsequently performed via linearly polarized, variable frequency microwave scattering off laser induced air-based microplasmas with diverse ionization and collisional features. Namely, conducted studies include a verification of short-dipole-like radiation behavior, plasma volume imaging via intensified charge-coupled device (ICCD) photography, and measurements of relative phases, total scattering cross sections, and total number of electrons $N_e$ in the generated plasma filaments following absolute calibration using a dielectric scattering sample. Findings of the paper suggest an ideality of the diagnostic in the Thomson "free-electron" regime - where a detailed knowledge of plasma and collisional properties (which are often difficult to accurately characterize due to the potential influence of inhomogeneities, local temperatures and densities, present species, and so on) is unnecessary to extract $N_e$ from the scattered signal.

physics.plasm-ph↗

arXiv2021

Transitional layer at the edge of a false vacuum in a cavitation model of the Big Bang

This paper considers the structure and physical processes in the transition region at the border between the regions of false and physical vacuums in a cavitation model of the inflationary stage of the Big Bang. It is shown that in the process of the formation of physical vacuum bubbles in a false vacuum, conditions for the formation of a narrow layer filled with matter arise in the transition region, which is the precursor to bridges in the observed large-scale cellular structure of the universe.

gr-qc↗

arXiv2020

Cavitation model of the initial stage of Big Bang

In this paper, we propose a model for the initial stage of the development of the Universe, analogous to cavitation in a liquid in a negative pressure field. It is assumed that at the stage of inflation, multiple breaks of the metric occur with the formation of areas of physical vacuum in which the generation of matter occurs. The proposed model explains the large-scale isotropy of the Universe without ultrafast inflationary expansion and the emergence of a large-scale cellular (cluster) structure, as a result of the development of cavitation ruptures of a false vacuum. It is shown that the cavitation model can be considered on par with (or as an alternative to) the generally accepted inflationary multiverse model of the Big Bang.

gr-qc↗

arXiv2019

Feasibility Study of a Laser-Based Approach for Diagnosing Deuterium Neutrals in the Edge of Fusion Devices

In magnetically-confined plasmas of tokamaks, neutral deuterium/hydrogen (D/H) atoms play a role in energy, momentum, and particle balance, as well as the stabilization of plasma turbulence. One key important fusion performance parameter is the pedestal density. Understanding the pedestal density formation is critical for the development of predictive model of future fusion devices. Typically, measurements of the neutrals are obtained using optical emission spectroscopy of the Lyman alpha lines, which is a line-integrated measurement. The plasma in tokamaks is characterized by a high density of electrons and ions and a relatively low concentration of neutral hydrogen atoms, which could make direct measurement of density seemingly impossible at first. We propose a laser-based method that allows for accurate measurement of both the spatial and absolute magnitude of the neutral D/H with minimal knowledge of the radial profiles of electron temperatures and densities. This relies on the fact that the neutral spectral profile can have a larger peak than the electron spectral profile and thus make the neutral density signal resolvable. In practice, this method can be co-located with Thomson scattering systems and is referred to as laser Rayleigh scattering (LRS). More specifically, we assess and evaluate the LRS method for two test cases: in the midplane radii of the National Spherical Torus Experiment (NSTX), and in the small angle slot divertor configuration of DIII-D. Preliminary simulations and calculations will determine the feasibility of LRS in the presence of incoherent Thomson scattering under neutral densities ranging from $ 10^{13} $ to $ 10^{21} \ \text{m}^{-3} $. Wavelength dependence of LRS will be evaluated to determine the boost in the signal and photon generation capability.

physics.app-ph↗

arXiv2019

Sub-barrier cavitation regime in liquid helium

In this paper, on the basis of the model Schrödinger equation, we consider the tunneling mechanism of cavitation in liquid helium and obtain threshold values of negative pressure as a function of temperature for 3He and 4He. The results of calculating the surface tension coefficients for flat and curved interfaces, obtained in the approximation of the Lenard-Jones interaction potential, are presented. It is shown that the temperature dependence of the critical pressure at which cavitation begins is stepwise in nature. The obtained critical pressure values are in satisfactory agreement with the experimental data.

cond-mat.other↗

arXiv2019

Thomson microwave scattering for electron number density diagnostics of miniature plasmas at low pressure

This work proposes a novel method of Thomson microwave scattering for electron number density measurements of miniature plasmas at pressures < 10 Torr. This method is applied to determine electron number density in a positive column of glow discharge initiated at 5 Torr in air with a plasma column diameter of 3.4 mm. The Thomson Microwave Scattering(TMS) system measured the electron number density to be 3.36*10^10 cm^-3. The result obtained using the TMS system was validated against the measurements made using the well-known technique of microwave quarter-wave hairpin resonator. Measurements with the hairpin resonator yielded an electron number density of 2.07*10^10 cm^-3 providing adequate agreement with the TMS system.

physics.plasm-ph↗

arXiv2019

On the possible mechanisms of the selective effect of a non-equilibrium plasma on healthy and cancer cells in a physiological solution

This paper discusses possible mechanisms for the selective effect of weakly ionized non-equilibrium plasma and currents in electrolyte on healthy and cancerous cells in physiological saline in a Petri dish. The interaction with the plasma source leads to a change in osmotic pressure, which affects the electro-mechanical properties of cell membranes in healthy and cancerous cells in different ways. The currents arising in the electrolyte charge the membranes of healthy and cancerous cells to a different potential difference due to the different values of the membranes' dielectric constant. We hypothesized that the dielectric permeability of cancer cell membranes is lower than that of healthy cells, as is the capacity of a unit of the membrane surface, and therefore, the additional potential difference acquired by the membrane through charging with currents induced in the intercellular electrolyte is greater in cancer cells. This can lead to electroporation of cancer cell membranes, resulting in their apoptosis, but does not effect healthy cells.

physics.bio-ph↗