Type Of Buffer Gas Research Articles

Collision Enhanced Raman Scattering (CERS): An Ultra-High Efficient Raman Enhancement Technique for Hollow Core Photonic Crystal Fiber Based Raman Spectroscopy Gas Analyzer.

Raman enhancement techniques are essential for gas analysis to increase the detection sensitivity of a Raman spectroscopy system. We have developed an efficient Raman enhancement technique called the collision-enhanced Raman scattering (CERS), where the active Raman gas as the analyte is mixed with a buffer gas inside the hollow-core photonic-crystal fiber (HCPCF) of a fiber-enhanced Raman spectroscopy (FERS) system. This results in an enhanced Raman signal from the analyte gas. In this study, we first showed that the intensity of the 587 cm-1 stimulated Raman scattering (SRS) peak of H2 confined in an HCPCF is enhanced by as much as five orders of magnitude by mixing with a buffer gas such as helium or N2. Secondly, we showed that the magnitudes of Raman enhancement depend on the type of buffer gas, with helium being more efficient compared to N2. This makes helium a favorable buffer gas for CERS. Thirdly, we applied CERS for Raman measurements of propene, a metabolically interesting volatile organic compound (VOC) with an association to lung cancer. CERS resulted in a substantial enhancement of propene Raman peaks. In conclusion, the CERS we developed is a simple and efficient Raman-enhancing mechanism for improving gas analysis. It has great potential for application in breath analysis for lung cancer detection.

Negative DC Dielectric Breakdown Characteristics and Synergistic Effect of HFO-1336mzz(E) Mixtures

HFO-1336mzz(E), a substitute for sulfur hexafluoride (SF6), has received much attention owing to its excellent insulation and environmental performance. To provide a reference for selecting suitable buffer gas type and mixing ratio in engineering applications, this article investigated the saturated vapor pressure characteristics, negative direct current (−dc) breakdown properties, and synergistic effect of HFO-1336mzz(E)/CO2 and HFO-1336mzz(E)/N2 mixtures. Experimental results show that although the allowable percentage of HFO-1336mzz(E) in the HFO-1336mzz(E)/CO2 mixture is lower than that of the HFO-1336mzz(E)/N2 at the same gas pressure and limiting temperatures, the former one has a higher breakdown voltage in the gas pressure range from 0.1 to 0.7 MPa. Compared with HFO-1336mzz(E)/N2, the shorter distance within the bimolecular composite structures of HFO-1336mzz(E)/CO2 leads to stronger interaction energy ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {int}}$ </tex-math></inline-formula> ). As a result, HFO-1336mzz(E)/CO2 has a better synergistic effect in view of breakdown voltage. Based on the comprehensive analysis of saturated vapor pressure, liquefaction temperature, and insulation properties of HFO-1336mzz(E)/buffer gas mixtures, CO2 is superior as a buffer gas to N2 being mixed with HFO-1336mzz(E). The negative dc breakdown voltage of 0.7 MPa HFO-1336mzz(E)/CO2 occupies 99.17%, 93.03%, and 85.92% of that of 0.7 MPa 20%SF6/80%N2 mixture under −5 °C, −15 °C, and −25 °C limiting temperatures, guaranteeing its application as an insulation medium in electrical equipment under 220 kV.

Remote Lasing in Humid Air from Atomic Hydrogen

Over the last few years, air lasing has emerged as an attractive topic in standoff detection research. However, existing approaches have relied on the major species of air as the gain medium. This work presents the first experimental demonstration of an air laser based on water vapor, a minor constituent of air. The approach relies on photodissociation of water vapor molecules followed by two-photon pumping of the constituent hydrogen atoms to produce lasing on the well-known Balmer-alpha line. This hydrogen laser is characterized in both the forward as well as return direction, and this paper discusses the effect of some parameters, including the presence and type of buffer gas, as well as the pump beam focusing. It is found that most of these results can be explained in terms of their influence on the gain of the stimulated emission process. This method can be potentially applied to other hydrogen-containing molecules and offers a promising approach for standoff detection of trace species.

Strategies for Scalable Gas-Phase Preparation of Free-Standing Graphene

The preparation of graphene with high quality serves as a prerequisite for its usage. Traditional methods of graphene production, represented by liquid-phase exfoliation and chemical vapor depositi...

Various buffer gas effects on amplifying parameters of a copper bromide laser

A pair of Copper Bromide lasers in an oscillator–amplifier configuration was used to study the dependence of the small-signal gain (g0), saturation energy intensity (Es) and output power on various types of Buffer gases in CuBr vapor lasers. The amplifying parameters and output power of the system were measured at different buffer gas pressure and the optimum pressure of 11, 17 and 23 torr were obtained for He, He–Ne and Ne, respectively. The values of these parameters were different for various gases used in the gain medium. It was shown that the use of He has more efficient and output power than that of Ne or their mixed ones in CuBr lasers. The type of buffer gas used in the gain medium can affect the microscopic parameters, which in turn affects the operation and output power.

Buffer gas effects on output power of a copper vapor laser

A copper vapor laser with an active medium length of 60 cm and bore of 16 mm was operated and optimized using different buffer gases to investigate the effect of pressure and gas flow rates on the laser output power. It was shown that a special interval of operational pressure and an optimum gas flow rate associated with the type of buffer gas were obtained.

Experimental Study of Buffer Gas Flow Rate Effect on Output Power of a Copper Vapor Laser

A copper vapor laser with active medium length of 60 cm and bore of 16 mm has been operated and optimized using different buffer gases to investigate the effect of the gas flow rates on the output power. It is found that there is a special optimum gas flow rate associated with the type of buffer gas.

Multi-photon UV photolysis of gaseous polycyclic aromatic hydrocarbons: Extinction spectra and dynamics

The extinction spectra of static naphthalene and static biphenylene vapor, each buffered with a noble gas at room temperature, were measured as a function of time in the region between 390 and 850 nm after UV multi-photon laser photolysis at 308 nm. Employing incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS), the spectra were found to be unstructured with a general lack of isolated features suggesting that the extinction was not solely based on absorption but was in fact dominated by scattering from particles formed in the photolysis of the respective polycyclic aromatic hydrocarbon. Following UV multi-photon photolysis, the extinction dynamics of the static (unstirred) closed gas-phase system exhibits extraordinary quasi-periodic and complex oscillations with periods ranging from seconds to many minutes, persisting for up to several hours. Depending on buffer gas type and pressure, several types of dynamical responses could be generated (classified as types I, II, and III). They were studied as a function of temperature and chamber volume for different experimental conditions and possible explanations for the oscillations are discussed. A conclusive model for the observed phenomena has not been established. However, a number of key hypotheses have made based on the measurements in this publication: (a) Following the multi-photon UV photolysis of naphthalene (or biphenylene), particles are formed on a timescale not observable using IBBCEAS. (b) The observed temporal behavior cannot be described on basis of a chemical reaction scheme alone. (c) The pressure dependence of the system's responses is due to transport phenomena of particles in the chamber. (d) The size distribution and the refractive indices of particles are time dependent and evolve on a timescale of minutes to hours. The rate of particle coagulation, involving coalescent growth and particle agglomeration, affects the observed oscillations. (e) The walls of the chamber act as a sink. The wall conditions (which could not be quantitatively characterized) have a profound influence on the dynamics of the system and on its slow return to an equilibrium state.

Dependences of small-signal gain and saturation-energy intensity on laser active length, buffer-gas type, and pressure variations in gold-vapor lasers

We measure the small-signal gain coefficient g0 and the saturation-energy intensity Es of a gold-vapor laser by implementing an oscillator-amplifier on the base of the gold-vapor laser. The dependence of the gain and saturation properties of the laser on the length of the laser active medium, the buffer-gas pressure, and the buffer-gas type are studied. The measurements of g0 for the amplifier for different lengths of the laser active medium (60 and 75 cm) show that with increase in the active-medium length, g0 increases while Es, vice versa, decreases. Such behavior of g0 and Es is observed in the whole range of changing the total pressure of buffer gas in the He-Ne mixture.

Study of the dependence of the specific output power of a copper chloride laser on the radial temperature profile of a gas plasma

The design of a copper chloride laser is described, and the laser is optimised by studying the dependence of its output power on the buffer gas type. The voltage and current of the laser discharge at the optimum buffer gas pressure are measured. The influence of the diaphragm diameter on the specific output power is studied after optimisation of switch parameters. When an diaphragm producing the optimal temperature gradient in the laser gas-discharge tube, the record specific output power of 123 W L-1 is obtained without any admixtures.

A Parametric Study of Single-Wall Carbon Nanotube Growth by Laser Ablation

Results of a parametric study of carbon nanotube production by the double-pulse laser oven process are presented. The effect of various operating parameters on the production of single-wall carbon nanotubes (SWCNTs) is estimated by characterizing the nanotube material using analytical techniques, including scanning electron microscopy, transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. The study included changing the sequence of the laser pulses, laser energy, pulse separation, type of buffer gas used, operating pressure, flow rate, inner tube diameter, as well as its material, and oven temperature. It was found that the material quality and quantity improve with deviation from normal operation parameters such as laser energy density higher than 1.5 J/cm2, pressure lower than 67 kPa, and flow rates higher than 100 sccm. Use of helium produced mainly small diameter tubes and a lower yield. The diameter of SWCNTs decreases with decreasing oven temperature and lower flow rates.

Unusual kinetics of ions in a discharge plasma: ambipolar diffusion and mobilities of ArD + in argon, helium and neon

Infrared diode laser kinetic spectroscopy has been employed for measurement of the decay of ArD + ions. The lifetime of ArD + increases with increasing buffer gas pressure from 20 to 100 μs in a cylindrical (radius 7.5 and 10.5 mm) glow discharge plasma and, from 200 to 600 μs in a hollow cathode (radius 20 mm) discharge plasma. The changes in ArD + lifetime range from 7.9 to 92 μs/ torr and depend on the type of buffer gas (Ne, He, Ar) and cell radius. The unusual kinetics of ArD + is controlled by ambipolar diffusion and by the ion mobilities.

Laser photoacoustic spectrometer for remote monitoring of atmospheric pollutants

An acoustically resonant CO(2) laser photoacoustic (PA) spectrometer for remote or in situ monitoring of air pollutants has been designed. The salient features of this PA system, along with the optimization tests of various operating parameters that affect the PA signal (buffer-gas pressure, type of buffer gas, laser power, gas concentration, and acoustic modes), are described. The system has been applied for the detection of pollutants emitted from the exhaust of a car located at a remote distance. Also, an alarm system based on the PA detection technique has been built for leak detection of toxic gases at industrial complexes. The minimum detectable concentration of C(2) H(4) and SO(2) with this system is 50 parts in 10(12) by volume and 50 parts in 10(9) by volume, respectively.

Design and Fabrication of Externally heated Copper Bromide Laser

An externally-heated, longitudinally-discharged, low-repetition-rate copper bromide laser, was designed and fabricated. The green-coloured wavelength at 5106 A from this laser can be used for underwater ranging and detection of submerged objects. Several new changes in the design of discharge tube, heating technique, buffer-gas-flow sub-system and electrical circuit have been conceived and incorporated advantageously in our system. Various parameters, for example, the type of buffer gas and its flow rate, mixture of gases, temperature of the discharge tube, delay between dissociation and excitation pulses, dissociation and excitation energies, and various resonator configurations are being optimised to get the maximum output power/energy from the laser system.

Spectroscopic Diagnostics and Kinetics of Low Pressure Processing Plasmas

AbstractA review is presented of a negative glow model of low frequency, low pressure plasma reactors and the salient features are described using silane mixtures as the example.The input requirements for this model and similar models are also discussed in order to establish the sensitivity of the homogeneous plasma reactions to operational conditions.Calculations are presented to demonstrate the sensitivity to mixture ratios, buffer gas type and power loading.

Electron-beam-controlled atomic Xe infrared laser

A study was made of a high-power high-pressure electron-beam-controlled laser utilizing the 5d-6p and 7p-7s transitions of the Xe atom and having an active volume of 9 liters. The dependences were obtained of the electrical parameters of an electron-beam-controlled discharge and of the energy parameters and spectral composition of the output radiation on the type of buffer gas, the discharge circuit parameters, and the composition and pressure of the active mixture. When the medium was pumped by an electron beam alone, having a current density of ~ 6 A/cm2 and a pulse duration of O.7 μsec, the laser output energy was ~ 6/J (efficiency ~ 1.5%), but for electronbeam- controlled pumping it was roughly 20 J. The physical lasing efficiency, in terms of the electric field, was ~5%. An analysis was made of the mechanism of the establishment of the active medium conductivity and of the population kinetics of the active transition levels.

Stimulated emission from the XeCl* molecule excited by an electron beam

Results are presented of an investigation of stimulated emission from the XeCl* molecule excited by an electron beam. Determinations were made of the influence of the pump density, mixture composition and pressure, and of the type of buffer gas (He, Ne, Ar, Kr) and chlorine carrier (CCl4, CHCl3, CF2Cl2) on the radiation energy and pulse duration, and also on the delay of the radiation pulse relative to the electron beam current. A radiation power of 11 MW and a specific radiation energy of ~10 J/liter were obtained. An analysis was made of the formation mechanism of XeCl* molecules.

A copper laser using CuI vapor

A simple CuI double-pulsed laser was built. The dependence of power output on the delay between the two excitation pulses, temperature, and the type of buffer gas has been investigated. The laser pulse duration was measured.

Gain characteristics of CO&amp;lt;inf&amp;gt;2&amp;lt;/inf&amp;gt;laser amplifiers at 10.6 microns

Single-pass gain at 10.6 microns has been studied parametrically in nonflowing CO 2 or buffered CO 2 amplifying media. The gain profile across the amplifier diameter and integrated gain both were determined. Parameters varied included buffer gas type, mixture ratio, gas pressure, amplifier bore, discharge current, and wall temperature. Tube bores of 12, 22, and 34 mm and buffer gases of H 2 , He, Ne, A, and N 2 were studied. Optimum gain is relatively independent of current density, but decreases with increasing wall temperature. The pressure-diameter relationship P_{CO_{2}} \cdot D \sim 4 torr-cm was found to hold for CO 2 , CO 2 :He, and CO 2 :N 2 amplifying media at optimum gain. The gain depends strongly on the CO 2 partial pressure and is relatively insensitive to the buffer gas pressure except for the case of H 2 . The maximum gain decreased slowly with increasing amplifier diameter. The highest gain, 1.7 dB/meter, was achieved with a helium buffer gas in amplifiers with a diameter of 22 mm or less. No gain saturation was detected for a 30-dB range of input signal power, from a milliwatt to a few watts. Spectrograms showed that the principal spontaneous emission from CO 2 :He amplifiers in the 2000-7000-A range consisted of CO bands; no CO 2 bands or He line spectra were observed.