Generation of strong-field spectrally tunable terahertz pulses.

The ideal laser source for nonlinear terahertz spectroscopy offers large versatility delivering both ultra-intense broadband single-cycle pulses and user-selectable multi-cycle pulses at narrow linewidths. Here we show a highly versatile terahertz laser platform providing single-cycle transients with tens of MV/cm peak field as well as spectrally narrow pulses, tunable in bandwidth and central frequency across 5 octaves at several MV/cm field strengths. The compact scheme is based on optical rectification in organic crystals of a temporally modulated laser beam. It allows up to 50 cycles and central frequency tunable from 0.5 to 7 terahertz, with a minimum width of 30 GHz, corresponding to the photon-energy width of ΔE=0.13 meV and the spectroscopic-wavenumber width of Δ(λ-1)=1.1 cm-1. The experimental results are excellently predicted by theoretical modelling. Our table-top source shows similar performances to that of large-scale terahertz facilities but offering in addition more versatility, multi-colour femtosecond pump-probe opportunities and ultralow timing jitter.

Catastrophic damage in hollow core optical fibers under high power laser radiation.

The propagation of an optical discharge (OD) along hollow-core optical fibers (HCFs) is investigated experimentally. Silica-based revolver-type HCFs filled with atmospheric air were used as test samples. We observed that the average propagation velocity of an OD along the HCF (VAV) depends on the properties of the medium around the silica structure of the fiber. It is shown that the value of VAV changes by approximately a factor of three, depending on whether the optical discharge is moving along a polymer coated or uncoated fiber. The value of VAV practically does not change when the polymer is replaced by an immersion liquid (such as glycerol) or liquid gallium. By analyzing the destruction region's patterns that appear in the fiber cladding after an OD propagation, we propose the physical picture of the phenomenon.

Damage in a Thin Metal Film by High-Power Terahertz Radiation.

We report on the experimental observation of high-power terahertz-radiation-induced damage in a thin aluminum film with a thickness less than a terahertz skin depth. Damage in a thin metal film produced by a single terahertz pulse is observed for the first time. The damage mechanism induced by a single terahertz pulse could be attributed to thermal expansion of the film causing debonding of the film from the substrate, film cracking, and ablation. The damage pattern induced by multiple terahertz pulses at fluences below the damage threshold is quite different from that observed in single-pulse experiments. The observed damage pattern resembles an array of microcracks elongated perpendicular to the in-plane field direction. A mechanism related to microcracks' generation and based on a new phenomenon of electrostriction in thin metal films is proposed.

Giant self-induced transparency of intense few-cycle terahertz pulses in n-doped silicon.

The results of high-field terahertz transmission experiments on n-doped silicon (carrier concentration of 8.7×1016 cm-3) are presented. We use terahertz pulses with electric field strengths up to 3.1 MV cm-1 and a pulse duration of 700 fs. A huge transmittance enhancement of ∼90 times is observed with increasing of the terahertz electric field strengths within the range of 1.5-3.1 MV cm-1.

Generation of 0.9-mJ THz pulses in DSTMS pumped by a Cr:Mg2SiO4 laser.

We report on high-field terahertz transients with 0.9-mJ pulse energy produced in a 400 mm² partitioned organic crystal by optical rectification of a 30-mJ laser pulse centered at 1.25 µm wavelength. The phase-locked single-cycle terahertz pulses cover the hard-to-access low-frequency range between 0.1 and 5 THz and carry peak fields of more than 42 MV/cm and 14 Tesla with the potential to reach over 80 MV/cm by choosing appropriate focusing optics. The scheme based on a Cr:Mg2SiO4 laser offers a high conversion efficiency of 3% using uncooled organic crystal. The collimated pump laser configuration provides excellent terahertz focusing conditions.

Nonthermal plasma affects viability and morphology of Mycoplasma hominis and Acholeplasma laidlawii.

AIM: To study the effects exerted by argon microwave nonthermal plasma (NTP) on cell wall-lacking Mollicutes bacteria. METHODS AND RESULTS: 10(8) CFU ml(-1) agar plated Mycoplasma hominis and Acholeplasma laidlawii were treated with the nonthermal microwave argon plasma for 30-300 s. The maximal 10- and 100-fold drop was observed for A. laidlawii and Myc. hominis, respectively. Similarly treated Escherichia coli and Staphylococcus aureus demonstrated the 10(5) and 10(3) drop, respectively. Removal of cholesterol affected resistance of A. laidlawii. 10 mmol l(-1) antioxidant butylated hydroxytoluene decreased mortality by a factor of 25-200. UV radiation alone caused 25-85% mortality in comparison with the whole NTP. Exogenously added hydrogen peroxide H2O2 did not cause mortality. NTP treatment of Myc. hominis triggered growth of microcolonies, which were several tenfold smaller than a typical colony. CONCLUSIONS: Despite the lack of cell wall, A. laidlawii and Myc. hominis were more resistant to argon microwave NTP than other tested bacteria. Mycoplasma hominis formed microcolonies upon NTP treatment. A role of UV and active species was demonstrated. SIGNIFICANCE AND IMPACT OF THE STUDY: The first study of NTP effects on Mollicutes revealed importance of a membrane composition for bacterial resistance to NTP. New specific Myc. hominis morphological forms were observed. The study confirmed importance of the concerted action of reactive oxygen species (ROS) with UV and other plasma bioactive agents for NTP bactericidal action.

Quantum bound of the shear viscosity of a strongly coupled plasma.

String theory methods led to the hypothesis that the ratio of a shear viscosity coefficient to the volume density of entropy of any physical system has a lower bound. Systems with strong coupling have a small viscosity as compared to weakly coupled plasmas in which the viscosity is proportional to the mean free path. Here, we have estimated the fully ionized strongly coupled plasma viscosity based on the dynamic experimental data on electrical conductivity and have shown that the ratio of viscosity to entropy of the strongly coupled plasma is very close to that of the lower bound predicted by the string theory.

Viscosity of a strongly coupled dust component in a weakly ionized plasma.

An experimental study of the kinematic viscosity has been carried out for dust particles of size 0.95 and 3.92 µm, in weakly ionized plasma over a wide range of dust coupling parameters. Measurements of viscosity for weakly correlated dusty-plasma systems are presented for the first time. An approximation for the estimation of viscosity constants is proposed. The measured viscosity constants are compared with theoretical estimates and numerical data.

Quantum phenomena in ignition and detonation at elevated density.

The influence of quantum effects on the processes of initiation of combustion and detonation of hydrogen and acetylene near the low-temperature limits at elevated pressures is analyzed. A theoretical consideration which allows quantification of the quantum corrections to the rate constants of endothermic reactions associated with an increase in the high-energy tail of the equilibrium momentum distribution function at high pressures is presented. This quantum effect is caused by a manifestation of the principle of uncertainty for the energy of the colliding particles at a high frequency of collisions. It is shown that significant deviations of experimentally observed ignition and detonation delay time from the predictions of kinetic calculations are quite well described by the proposed quantum corrections. This general mechanism should be considered in the safety problem with emergency emissions of hydrogen at nuclear power stations, as well as problems of the safe production and storage of hydrogen and acetylene, which have a fundamental importance for industry and power engineering.

Freezing and melting of 3D complex plasma structures under microgravity conditions driven by neutral gas pressure manipulation.

Freezing and melting of large three-dimensional complex plasmas under microgravity conditions is investigated. The neutral gas pressure is used as a control parameter to trigger the phase changes: Complex plasma freezes (melts) by decreasing (increasing) the pressure. The evolution of complex plasma structural properties upon pressure variation is studied. Theoretical estimates allow us to identify the main factors responsible for the observed behavior.

[Prospects for the use of low-temperature gas plasma as an antimicrobial agent].

Results of application of LTP at atmospheric pressure as an antibacterial agent during the last decade are considered with reference to physicochemical mechanisms of its bactericidal action. The principles of designing modern LTP sources are described in conjunction with the results of LTP application against pathogenic bacteria in vitro and in biofilms. The possibility to destroy biofilm matrix by LTP is estimated along with the results of its testing for the treatment of acute and chronic wound surfaces. Prospects for the development of "plasma medicine" in this country and abroad are discussed with special emphasis on its advantages, such as the absence of long-acting toxic compounds, small probability of spontaneous mutations accounting for resistance to LTP, relatively low cost of LTP sources, independence of LTP effect of the surface relief, painless application.

Long-term evolution of the three-dimensional structure of string-fluid complex plasmas in the PK-4 experiment.

Microparticle suspensions in a polarity-switched discharge plasma of the Plasmakristall-4 facility on board the International Space Station exhibit string-like order. As pointed out in [Phys. Rev. Research 2, 033314 (2020)2643-156410.1103/PhysRevResearch.2.033314], the string-order is subject to evolution on the timescale of minutes at constant gas pressure and constant parameters of polarity switching. We perform a detailed analysis of this evolution using the pair correlations and length spectrum of the string-like clusters (SLCs). Average exponential decay rate of the SLC length spectrum is used as a measure of string order. The analysis shows that the improvement of the string-like order is accompanied by the decrease of the thickness of the microparticle suspension, microparticle number density, and total amount of microparticles in the field of view. This suggests that the observed long-term evolution of the string-like order is caused by the redistribution of the microparticles, which significantly modifies the plasma conditions.

Colossal magnetic fields in high refractive index materials at microwave frequencies.

Resonant scattering of electromagnetic waves is a widely studied phenomenon with a vast range of applications that span completely different fields, from astronomy or meteorology to spectroscopy and optical circuitry. Despite being subject of intensive research for many decades, new fundamental aspects are still being uncovered, in connection with emerging areas, such as metamaterials and metasurfaces or quantum and topological optics, to mention some. In this work, we demonstrate yet one more novel phenomenon arising in the scattered near field of medium sized objects comprising high refractive index materials, which allows the generation of colossal local magnetic fields. In particular, we show that GHz radiation illuminating a high refractive index ceramic sphere creates instant magnetic near-fields comparable to those in neutron stars, opening up a new paradigm for creation of giant magnetic fields on the millimeter's scale.

Kinetics of fluid demixing in complex plasmas: role of two-scale interactions.

Using experiments and combining theory and computer simulations, we show that binary complex plasmas are particularly good model systems to study the kinetics of fluid-fluid demixing at the "atomistic" (individual particle) level. The essential parameters of interparticle interactions in complex plasmas, such as the interaction range(s) and degree of nonadditivity, can be varied significantly, which allows systematic investigations of different demixing regimes. The critical role of competition between long-range and short-range interactions at the initial stage of the spinodal decomposition is discussed.

Effect of trapped ions and nonequilibrium electron-energy distribution function on dust-particle charging in gas discharges.

Dust-particles charging in a low-pressure glow discharge was investigated theoretically. The dust-particle charge was found on the basis of a developed self-consistent model taking into account the nonequilibrium character of electron distribution function and the formation of an ionic coat composed of bound or trapped ions around the dust particle. The dust-particle charge, the radial distributions of electron density, free and trapped ions densities, and the distribution of electrostatic potential were found. It was shown that the non-Maxwellian electron distribution function and collisional flux of trapped ions both reduce the dust-particle charge in comparison with that received with the help of the conventional orbital motion limited (OML) model. However, in rare collisional regimes in plasma when the collisional flux is negligible, the formation of ionic coat around a particle leads to a shielding of the proper charge of a dust particle. In low-pressure experiments, it is only possible to detect the effective charge of a dust particle that is equal to the difference between the proper charge of the particle and the charge of trapped ions. The calculated effective dust particle charge is in fairly good agreement with the experimental measurements of dust-particle charge dependence on gas pressure.

Large Hadron Collider at CERN: Beams generating high-energy-density matter.

This paper presents numerical simulations that have been carried out to study the thermodynamic and hydrodynamic responses of a solid copper cylindrical target that is facially irradiated along the axis by one of the two Large Hadron Collider (LHC) 7 TeV/ c proton beams. The energy deposition by protons in solid copper has been calculated using an established particle interaction and Monte Carlo code, FLUKA, which is capable of simulating all components of the particle cascades in matter, up to multi-TeV energies. These data have been used as input to a sophisticated two-dimensional hydrodynamic computer code BIG2 that has been employed to study this problem. The prime purpose of these investigations was to assess the damage caused to the equipment if the entire LHC beam is lost at a single place. The FLUKA calculations show that the energy of protons will be deposited in solid copper within about 1 m assuming constant material parameters. Nevertheless, our hydrodynamic simulations have shown that the energy deposition region will extend to a length of about 35 m over the beam duration. This is due to the fact that first few tens of bunches deposit sufficient energy that leads to high pressure that generates an outgoing radial shock wave. Shock propagation leads to continuous reduction in the density at the target center that allows the protons delivered in subsequent bunches to penetrate deeper and deeper into the target. This phenomenon has also been seen in case of heavy-ion heated targets [N. A. Tahir, A. Kozyreva, P. Spiller, D. H. H. Hoffmann, and A. Shutov, Phys. Rev. E 63, 036407 (2001)]. This effect needs to be considered in the design of a sacrificial beam stopper. These simulations have also shown that the target is severely damaged and is converted into a huge sample of high-energy density (HED) matter. In fact, the inner part of the target is transformed into a strongly coupled plasma with fairly uniform physical conditions. This work, therefore, has suggested an additional very important application of the LHC, namely, studies of HED states in matter.

Self-consistent electric field inside ordered dust structures.

We report finding a self-consistent electric field of electrons, ions, and dust grains inside an ordered dust cloud in glow discharge, and show that this field differs radically from that of an isolated grain. Besides, the screening radius coincides with the size of Wigner-Seitz cell. The value of potential necessary for containing dust particles in the direction perpendicular to the discharge axis is estimated. We show that the interaction potential energy of a system of ordered dust grains has a form characteristic of ionic crystals. Critical parameters for a liquidlike dust structure are estimated. The correlation function of dust grains obtained via this approach is compared with the measured function.

Evolution of the mass-transfer processes in nonideal dissipative systems. I. Numerical simulation.

The results of numerical study of mass-transfer processes in quasi-two- and three-dimensional nonideal dissipative systems are presented. Simulations were performed for different types of model pair potentials of intergrain interaction that are various combinations of power-law and exponential functions. The calculations were performed in a wide range of parameters typical for laboratory dusty plasma experiments. It was shown that the dynamics of grains in liquidlike systems for short observation times is close to the evolution of thermal oscillations in the crystal lattice.

Evolution of the mass-transfer processes in nonideal dissipative systems II: experiments in dusty plasma.

The results of the experimental study of mass-transfer processes are presented for dust systems, forming in a laboratory plasma of a radio-frequency capacitive discharge. The validity of the Langevin and Green-Kubo equations for the description of the dynamics of dusty grains in laboratory plasma is verified. A method for simultaneous determination of dusty plasma parameters, such as the kinetic temperature of the grains, their friction coefficient, and characteristic oscillation frequency, is suggested. The coupling parameter of the system under study and the minimal values of the grain charges are estimated. The parameters of the dusty subsystem obtained (diffusion coefficients, pair correlation functions, charges, and friction coefficients of the grains) are compared with the existing theoretical and numerical data.

Attraction of positively charged particles in highly collisional plasmas.

It is shown that the electrostatic interaction potential between a pair of positively charged particles embedded in a highly collisional plasma has a long-range attractive asymptote. The effect is due to continuous plasma absorption on the particles. The relevance of this result to experimental investigations of complex (dusty) plasmas is discussed.