Absorption of radiation in a plasma by surface plasmons

In a plasma characterized by a sharp density discontinuity, energy from impinging radiation can be coupled to surface plasmons by surface rippling. These ripples can grow under the nonlinear ponderomotive force due to the surface plasmon field and the impinging field, with typical growth rates in the picosecond range.     

Application of surface-enhanced Raman in skin cancer by plasma

We have developed a mouse squamous cell carcinomas (SCC) model by diniethylbenzanthracene (DMBA) and ultraviolet (UVB). A silver colloid as SERS-active substrates is used for detecting the blood plasma of mouse. The relative intensity of the band at 942 and 1499 cm⁻¹ is higher in SCC model than in healthy one. Therefore, it can be used as an important “fingerprint” in order to diagnose these diseases. Results show us how to get high signal-to-noise ratio of biological macromolecules surface-enhanced Raman scattering spectra in blood plasma. And also offer useful help for understanding the rich molecular structure information in biological tissues. It provides a molecular spectroscopy way for early detection of disease in blood plasma.     

Electron-ion recombination in a helium plasma produced by laser

Experimental investigation of the recombination coefficients in a helium plasma produced by laser is reported. The relative contribution of electronic collision processes and of atomic collision processes on the values of the recombination coefficients are pointed out according to the value of the neutral pressure of helium.     

Role of helium in a He-Xe plasma

The populations of the 5p⁵6s and 5p⁵6p levels of Xe are reported as functions of current and partial pressure of He for the positive column of a glow discharge at medium pressures. The populations of the first ones (especially the metastable 5p⁵6s³P₂ one) decrease as the He pressure is raised, whereas those of the upper 5p⁵6p levels increase. An explanation is proposed for the observed changes in the level populations.We are indebted to Professor A. N. Tekuchev for direction and comments, and to Z. P. Gasko for help with the measurements.     

On the theory of Raman scattering in liquid helium

A modification of Stephen's theory is proposed which does not depend on any adjustable parameter. Numerical calculation of the Raman spectrum for free excitations shows that some interaction has to be taken into account in order to obtain detailed agreement with experiment.     

The influence of a self-focused laser beam on the stimulated Raman scattering process in collisional plasma

The influence of a self-focused beam on the stimulated Raman scattering(SRS) process in collisional plasma is explored. Here, collisional nonlinearity arises as a result of non-uniform heating, thereby causing carrier redistribution. The plasma density profile gets modified in a perpendicular direction to the main beam axis. This modified plasma density profile greatly affects the pump wave, electron plasma wave(EPW) and back-scattered wave. The well-known paraxial theory and Wentzel–Kramers–Bri...     

Recombination of doubly ionized atoms in the afterglow of a helium plasma produced by laser

Experimental investigation of the collisional-radiative decay coefficient of doubly ionized helium atoms in a helium plasma produced by laser is reported. Comparison of our experimental values with the theoretical values determined by Drawin-Emard is made. A reasonable agreement is obtained if we take into account the optical thickness of the plasma.     

Role of neon in a decaying high-purity helium plasma

The evolution of the electron and atomic and molecular metastable densities and the radiation of the decaying plasma of helium with a 10^–5-fraction of neon additive is experimentally studied. A model of elementary processes in He–Ne plasma is constructed, which describes the formation and destruction of HeNe⁺ and Ne₂ ⁺ molecular ions and their contribution to the formation of the afterglow spectrum by the electronion recombination. The various criteria influence of neon on the parameters of the decaying plasma are studied. The possibility of determining the amount of neon in helium by measuring the relative intensities of helium molecular bands and neon spectral lines in the afterglow is considered.     

Simulation of thermal ionization in a dense helium plasma by the Feynman path integral method

The region of equilibrium states is studied where the quantum nature of the electron component and a strong nonideality of a plasma play a key role. The problem of negative signs in the calculation of equilibrium averages a system of indistinguishable quantum particles with a spin is solved in the macroscopic limit. It is demonstrated that the calculation can be conducted up to a numerical result. The complete set of symmetrized basis wave functions is constructed based on the Young symmetry operators. The combinatorial weight coefficients of the states corresponding to different graphs of connected Feynman paths in multiparticle systems are calculated by the method of random walk over permutation classes. The kinetic energy is calculated using a viral estimator at a finite pressure in a statistical ensemble with flexible boundaries. Based on the methods developed in the paper, the computer simulation is performed for a dense helium plasma in the temperature range from 30000 to 40000 K. The equation of state, internal energy, ionization degree, and structural characteristic of the plasma are calculated in terms of spatial correlation functions. The parameters of a pseudopotential plasma model are estimated.     

利用介质阻挡探针法测量大气压氦等离子体射流电子密度

分别利用电子的漂移速度和等离子体的传播速度计算了大气压下氦等离子体射流的电子密度。     

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The electron densities in the atmospheric pressure helium plasma were calculated by means of electron drift velocity and the jet velocity respectively. The electron velocity and jet velocity can be calculated by means of helium plasma jet current measured by a dielectric probe and plasma discharge current signal measured by voltage probes. The results show that the estimated electron densities of the helium plasma jet calculated from electron drift velocity and the jet velocity are in the order of 10 ¹¹ cm ^-3 and they increase with applied voltage. There is a little fluctuation in the value of the electron density along the jet axis of the plasma. This result is the same as the measured electron density in atmospheric pressure helium non-thermal plasma jet by using a Rogowski coil and a Langmuir probe. This is in one order lower than the electron density measured by microwave antenna.     

On the mechanism of formation of helium molecules in a low-temperature plasma

The glow of He₂ molecules in a low-pressure (P ≤ 2 Torr) helium plasma excited by a monochromatic electron beam is detected and studied. The experimental data point to the existence of two basic mechanisms of formation of an excited He₂ molecule, namely, the collision of an excited helium atom with two unexcited atoms and the recombination of a molecular ion.     

Investigation of the energy-saving process of cement dispersion in a helium atmosphere

The process of commercial cement grinding in a helium atmosphere has been investigated in comparison with the process in an air atmosphere. Raw material particles have been sorted by sizes. Curves of helium release from the raw material after its grinding in air and in helium in the temperature range T = 20–1200°C have been constructed and analyzed. The influence of the character of water molecule adsorption on raw material cement particles before and after grinding in air and in helium and on the shape of helium release curves has been revealed.     

Measurements of electron density and Stark width of neutral helium lines in a helium arc plasma

Electron densities in an atmospheric helium arc plasma have been measured with the Stark broadening parameters of helium spectral lines. The spatially distributed radiation intensities are converted to plasma emission coefficients at every wavelength by means of Abel inversion. From the inverted profiles of He I lines of 4713 ?, 5016 ?, and 6678 ? electron density has been calculated, which ranges from 0.5 ×10¹⁶ to 4 ×10¹⁶ cm^-3 for a helium arc with current 200 A. Stark widths of He I lines of 3889 ? and 7065 ? are determined based on the measurements and compared with existing data.     

Observation of hydrogen and helium satellites in a turbulent plasma

Time-resolved measurements of satellites about the (1s2s?1s3d) forbidden transition in helium, satellites both of the H_δ line of hydrogen and of its splittings and, finally, satellites of He II 4868 Å have been observed. The behavior of these satellites is correlated relative to each other and to previously reported satellites both on H_β and near the 6632 Å (1s2p?1s3p) forbidden transition in helium. The appearance of the satellites is attributed to a strong field interaction between orthogonal components of the dynamic and quasistatic electric fields generated in a plasma by an instability.     

Stark broadening of visible neutral helium lines in a plasma

Side-on observations of the visible spectrum emitted by a helium plasma generated in a wall-stabilized arc are reported. Electron densities range from 0.2 to 1.3 × 10²²m^-3 and electron temperatures vary from 10,000 to 20,000 K. Most of the seventeen measured lines are “isolated” at the conditions of the experiment. Here, “isolated” refers to quantum levels which are non-degenerate even in the presence of perturbing fields. Electron densities derived from the Stark-widths of the isolated lines agree to within 15% of the values determined from Hβ and from the quasi-degenerate He(I) lines at 4471 and 4921 Å. Similar agreement is observed for the static-ion Stark broadening parameters. However, at the conditions of this experiment, the static-ion approximation is not valid near the center of some of the isolated lines. The observation of ion-dynamic effects in neutral isolated lines is reported here for the first time. In the isolated lines, the measured ion-dynamic effects are reasonably consistent with calculations based on an adiabatic “unified” theory for the ion perturbers. A simple parametric expression closely approximates the ion-dynamic contribution to the half-width of isolated lines. Hydrogenic (non-isolated) neutral helium lines exhibit a large discrepancy with theoretical profiles near the line center, where ion-dynamic effects are important.