Optical properties of mouse biotissues and their optical phantoms

The optical characteristics of a barrier discharge in a mixture of heavy water vapor with argon in the wavelength region 200–315 nm are presented. The dependence of the radiation intensity of the OD (A → X) band at λ = 309 nm on the partial pressure of the D₂O vapor is studied, the mechanism of hydroxyl formation in the plasma is considered, and optimal compositions of pollution-free and inexpensive mixtures based on Ar-D₂O are determined for application in UV lamps, which are promising for use in photomedicine.     

The Influence of Molecular Gas on the Apokamp Discharge Formation

Emission spectra of apokamp discharge plasma jets in CO₂, Ar, Kr, N₂, and their mixtures have been studied. It has been shown that the emission spectra of the Kr–N₂ mixture contain N₂ and \(\rm{N_2^+}\) bands, as well as Kr lines. The spectrum of the Ar–CO₂ mixture is presented by bands of the Fox–Duffendack–Barker system and lines of the exited argon atom. In all gas media under study, the reduction of the molecular gas quantity leads to the transition from an apokampic discharge in the form of a diffusion jet developing from the current channel to a volume discharge with a strong transverse glowing. The experimental apparatus described in this work is proposed for use in laboratory investigations of spectral characteristics of transient luminous events observed in atmospheres of planets of the Solar System.     

Spectroscopic Study of CO2 Decomposition in Sealed‐off CO2 Lasers

The CO₂ decomposition in a DC glow discharge in a sealed‐off CO₂ laser mixture (6% CO₂ : 20% N₂ : 74% He) in the pressure range 2 ‐ 22 Torr is investigated. Both the time evolution and the steady‐state CO₂ decomposition are studied by means of time resolved optical emission spectroscopy. A decrease of the time to reach steady‐state values of particles concentrations in the discharge system with decreasing pressure and increasing discharge current is observed. The degree of CO₂ decomposition rapidly decreases with increasing pressure and exhibits only a small increase with increasing discharge current. This behaviour can be explained by the variations of the reduced electrica field strength E/N and of the electron density. Also the influence of the balast volume is discussed in this work.     

DC corona discharge influence on chemical composition in mixtures of natural gas with air and its combustion exhaust with air

Experiments in dc supplied corona discharge in natural gas + air mixture and in combustion exhaust of natural gas + air mixture were realized. The influence of discharge on CO, CO₂, NO _x and other minority components was studied using IR absorption spectrometry. Production of NCO radicals in gas and consequent formation of NCO containing surface layers on a plate electrode was detected. In natural gas + air mixture after about 1 min oxygen poor combustion exhaust was produced due to slow combustion by corona discharge. Occurrence of various pulses in discharge current was typical.     

Formation of nanostructured carbon on steel targets irradiated by a high-power ion beam

The effect of the preliminary high-power ion beam treatment of steel targets (12KhN3A, St3, St20, St45) on the morphology and structure of a carbon layer produced by DC discharge plasma enhanced chemical vapor deposition using a C₂H₂/H₂ gas mixture has been investigated. It has been found that carbon nanotubes are formed on the St3 and St20 surface irradiated by the high-power ion beam with the ion current densities 50 and 100 A/cm².     

Numerical solution of Boltzmann tranport equation for TEA CO2 laser having nitrogen-lean gas mixtures to predict laser characteristics and gas lifetime

Selective laser isotope separation by TEA CO₂ laser often needs short tail-free pulses. Using laser mixtures having very little nitrogen almost tail free laser pulses can be generated. The laser pulse characteristics and its gas lifetime is an important issue for long-term laser operation. Boltzmann transport equation is therefore solved numerically for TEA CO₂ laser gas mixtures having very little nitrogen to predict electron energy distribution function (EEDF). The distribution function is used to calculate various excitation and dissociation rate of CO₂ to predict laser pulse characteristics and laser gas lifetime, respectively.Laser rate equations have been solved with the calculated excitation rates for numerically evaluated discharge current and voltage profiles to calculate laser pulse shape. The calculated laser pulse shape and duration are in good agreement with the measured laser characteristics. The gas lifetime is estimated by integrating the equation governing the dissociation of CO₂. An experimental study of gas lifetime was carried out using quadrapole mass analyzer for such mixtures to estimate the O₂ being produced due to dissociation of CO₂ in the pulse discharge. The theoretically calculated O₂ concentration in the laser gas mixture matches with experimentally observed value. In the present TEA CO₂ laser system, for stable discharge the O₂ concentration should be below 0.2%.     

Heat transfer between tungsten surface and glow discharge plasmas in argon and CO<Subscript>2</Subscript>

A hot-filament method is used to study the heat transfer between tungsten surface and hollow-cathode glow discharge plasmas in argon and CO₂. The dependence of the electric power supplied to a tungsten wire on the discharge current is determined for argon and carbon dioxide in the temperature range between 1000 and 1700 K. A difference in heat transfer at the tungsten wire surface is found between experiments on argon and carbon dioxide. The difference is attributed to heterogeneous recombination in CO₂ plasma.     

Emission characteristics of a gas-discharge plasma of water vapor in the vacuum UV region of the spectrum

We present the results of a study of emission from a low-density water vapor plasma in the vacuum ultraviolet (VUV) region of the spectrum. The plasma was formed in a longitudinal glow discharge. We have studied the spectral characteristics of the plasma and also the dependences of the relative energy characteristics of the hydroxyl (OH) emission band on the discharge current and the helium partial pressure in a He-H₂O mixture in the spectral range 130–190 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 831–833, November–December, 2006.     

Burning carbon monoxide in the settling chamber of a hotshot wind tunnel for obtaining the CO<Subscript>2</Subscript> test gas

A method of formation and heating of CO₂ as a test gas in the settling chamber of a hotshot wind tunnel is considered. To form and heat CO₂, the chamber is filled with a source gas mixture of CO, O₂, and CO₂, and after initiation, these substances participate in an exothermic chemical reaction in accordance with the formula CO + 0.5 O₂ + xCO₂ = (1 + x)CO₂. A stoichiometric ratio of the concentrations of carbon monoxide CO and oxygen is used. Variation of the number of moles x of ballast CO₂ in the left part of the chemical formula allows changing the temperature of the resultant test gas in a wide range. Experiments in the IT-302M hotshot wind tunnel carried out at ITAM SB RAS have shown that a pressure increase during an isochoric process in the settling chamber due to the joint effect of heat released in the reaction CO + 0.5 O₂ and an electric charge provides the completeness of CO combustion almost equal to unity. The time of reaction completion at its initiation by an electric arc is no more than several milliseconds.     

Graphite gasification in high-temperature gas flows containing H<Subscript>2</Subscript>O and CO<Subscript>2</Subscript>

The rates of graphite gasification in interaction with high-temperature gas flows were compared. Carbon dioxide and a mixture of water vapor and argon taken in a 1:1 molar ratio were used as reagents. The reactor was a tube furnace; its temperature was varied from 1250 to 1400 K. The rates of graphite gasification in CO₂ and water vapor-argon mixture flows were approximately equal at 1250–1300 K, whereas, at 1350–1400 K, the water vapor-argon mixture exhibited higher reactivity than CO₂. The data obtained were approximated by Arrhenius dependences; the activation energy was found to be 153 kJ/mol for CO₂ and 248 kJ/mol for H₂O-Ar.     

Emission characteristics of pulse-periodic barrier-discharge plasma in a mixture of krypton with argon and liquid freon vapor

Radiation of a nanosecond barrier discharge in a mixture of krypton, argon, and carbon-tetrachloride vapor is studied in the spectral range of 150–300 nm. The plasma radiation spectra and the dependences of the intensities of the 258 nm Cl₂(D′ → A′), 222 nm KrCl(B → X), and 175 nm ArCl(B → X) bands on the partial pressure of liquid freon vapor, argon, and krypton, as well as on the discharge excitation conditions, are studied. The optimal compositions of gas mixtures for creating a broadband UV-VUV emitter based on the band system of argon chloride, krypton chloride, and chlorine molecule are determined.     

Optical characteristics and parameters of a gas discharge plasma based on a mixture of mercury dibromide vapor and helium

We present the results of studies of the optical characteristics and parameters of a gas discharge plasma produced by a barrier discharge at atmospheric pressure, based on a mixture of mercury dibromide vapor and helium (the working medium of a small (emitting area 8 cm²) exciplex gas discharge emitter). An average emission power of 70 mW (λ_max = 502 nm) was achieved for pump pulse repetition frequency 6 kHz, voltage pulse amplitude 2.3 kV, and current pulse amplitude 8 A of duration ~100 nsec. We established the plasma parameters: the electron energy distribution functions, the transport characteristics, the discharge power losses per unit pressure going toward electron processes, the electron concentration and temperature, and also the rate constants for processes of elastic and inelastic scattering of electrons by the components of the working mixture as a function of the parameter E/N, where E is the electric field strength and N is the total concentration of mercury dibromide molecules and helium atoms.     

Emission characteristics of a glow discharge in a mixture of heavy inert gases with iodine vapor

The results of a systematic investigation of the emission characteristics of a low-pressure UV excimer-halogen lamp pumped by a longitudinal dc glow discharge are presented. The discharge was initiated in mixtures of heavy inert gases with iodine vapor at a total pressure of 100–2000 Pa and a power deposited into the plasma of 10–100 W. Current-voltage characteristics of the glow discharge and emission spectra of the plasma in the region of 190–360 nm are studied. The radiation intensity at the resonance line of the iodine atom (206.2 nm) and the intensity at the peaks of the XeI(B-X) (253 nm) and I₂(B-X) (342 nm) emission bands are analyzed as functions of the pressure and partial composition of the mixtures of Ar, Kr, and Xe with iodine vapor, as well as the electric power of the glow discharge. The most efficient gas mixtures are determined for an electric-discharge UV iodine vapor lamp with continuous-wave emission and a long service life before a change of the mixture is required.     

A study of the gasification of carbon black with molten salt of Li2CO3 and K2CO3 for application in the external anode media of a direct carbon fuel cell

The characteristics of gasification reactions for carbon–carbonate mixtures were experimentally investigated at high temperatures up to 900 °C, considering the application of the mixtures to the external anode media of a direct carbon fuel cell. A thermo-gravimetric analysis (TGA) was conducted in either a nitrogen or carbon dioxide ambient environment for Li₂CO₃, K₂CO₃ and a mixture of these two substances with carbon black. Changes in the exit gas composition were also monitored during the heating process. It was shown that gasification in the mixture media occurs much more rapidly than carbonate decomposition at elevated temperatures, even for low concentrations of CO₂. It was also shown that the loading of carbonates to carbon significantly affects the global gasification reaction; it increased the reaction rate by an order of magnitude and decreased its activation energy. Based on the experimental observations, a simplified reaction model of gasification was suggested for the anode media of a DCFC, regarding carbonate-catalysed and metal-catalysed pathways of Boudouard reactions.     

PECVD of Carbon Nanostructures in Hydrocarbon‐Based RF Plasmas

Different aspects of the plasma‐enhanced chemical vapor deposition of various carbon nanostructures in the ionized gas phase of high‐density, low‐temperature reactive plasmas of Ar+H₂+CH₄ gas mixtures are studied. The growth techniques, surface morphologies, densities and fluxes of major reactive species in the discharge, and effects of the transport of the plasma‐grown nanoparticles through the near‐substrate plasma sheath are examined. Possible growth precursors of the carbon nanostructures are also discussed. In particular, the experimental and numerical results indicate that it is likely that the aligned carbon nanotip structures are predominantly grown by the molecular and radical units, whereas the plasma‐grown nanoparticles are crucial components of polymorphous carbon films. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of gas detection based on integrated cavity output spectroscopy

A trace gases detection system based on integrated cavity output spectroscopy (ICOS) was developed, where a NIR tunable diode laser (TDL) was used as light source, an optical cavity composed by two plan-concave mirrors with reflection near 99.7% was used as the absorption cell. Trace water vapour (H₂O), carbon dioxide (CO₂), methane (CH₄), carbon monoxide (CO) and mixture of CO₂ and CO were tested by ICOS based on the characteristics absorption. The wavelength calibration, cavity transmission characteristics, quantitative measurement ability and sensitivity of the TDL-ICOS were also studied, and a evaluated minimum detectable sensitivity of 1.15 × 10^?7 cm^?1 was obtained when the system was used to CH₄ detection. The experiment results show that TDL-ICOS is expected to be a reliable and promising system for the detection of trace gases since it has some advantages such as real-time monitoring, simple device, easy operation, high sensitivity, good stability and quantitative ability.     

Short delay time UV preionized TEA CO2 laser operating with binary CO2/H2 and CO2/He gas mixtures

In order to obtain short tail-free output laser pulses from a TEA CO₂ laser, parametric study of the laser operation with CO₂/H₂ and CO₂/He binary gas mixtures containing high CO₂ concentrations was carried out. A small scale UV preionized short delay time TEA CO₂ laser was employed. In terms of the maximum extractable output pulse energy and power, the more conventional CO₂/He gas mixture was found to be inferior in comparison with the CO₂/H₂ mixture proposed here.     

Theoretical and experimental study of V–I characteristics of UV pre-ionized TEA CO2 laser for variety of laser gas mixtures

Experimental and theoretical study of V–I characteristics of UV pre-ionized TEA CO₂ laser has been carried out for a variety of gas mixtures emitting different optical pulse shapes suitable for various applications. Coupled differential equations have been solved to model the pulse excitation circuit using the numerically calculated values of ionization coefficient (α), attachment coefficient (β) and drift velocity (U_d) as functions of E/N (i.e. electric field to neutral particle density ratio) for chosen gas mixture. Calculated and experimental V–I characteristics for gas mixtures (CO₂:N₂:He::1:2:3, 1:1:4, 1:1:5 and 1:0:4.7) show a good agreement. It has been shown that gas mixture has a dominant effect on the delay between pre-ionization and main discharge; thus, determining the long-term stability of discharge. The excitation pulse duration increases with increase in molecular content of gas mixture (i.e. amount of CO₂ and N₂ in gas mixture).     

Emission characteristics of a barrier discharge in an Ar-H2O mixture

We have experimentally studied the UV radiation of a low-temperature barrier discharge plasma in an Ar-H₂O mixture. The spectral interval 300–400 nm has been examined in detail. Addition of argon with a pressure of 24 kPa to a barrier discharge in water vapor at a pressure of ～0.1 kPa leads to a ninefold increase in the UV radiation power of excited hydroxyl molecules. An increase in the duration of the UV radiation pulse of the mixture in the longitudinal discharge decay has been achieved for the first time, which may be direct evidence of energy transfer from metastable argon atoms to water molecules. An estimate of the upper boundary of the dissociative excitation rate constant of hydroxyl molecules OH*(A ²Σ⁺) upon interaction of metastable argon atoms with water molecules has been obtained.     

H2， He混合稀释生长微晶硅锗薄膜

采用H₂,He混合气体稀释等离子辅助反应热化学气相沉积法生长微晶硅锗薄膜,并在生长过程中对等离子体进行光发射光谱在线监测.结果表明：混合气体稀释法可以有效提高等离子体中的原子氢数目,降低等离子体中的电子温度;用XRD和光暗电导率表征样品的微结构和光电特性时发现,通过优化混合稀释气体中He和H₂气体的比例,能够减少薄膜中的缺陷态,促进薄膜<220>择优取向生长,有效改善微晶硅锗薄膜结构,提高光电吸收性能. 关键词： 化学气相沉积 微晶硅锗薄膜 光发射光谱 X射线衍射