Comparative Study on Excitation Mechanism of Chromium Emission Lines in Argon Radio‐Frequency Inductively‐Coupled Plasma,Nitrogen Microwave Induced Plasma,and Argon or Nitrogen Glow Discharge Plasmas

Boltzmann plots of both atomic and ionic chromium emission lines are investigated to compare the excitation mechanisms in four different plasmas: an argon inductively‐coupled plasma (Ar‐ICP), a nitrogen high‐power microwave induced plasma (N₂‐MIP), an argon glow discharge plasma (Ar‐GDP), and a nitrogen glow discharge plasma (N₂‐GDP). The plots of the atomic lines and the ionic lines give both linear relationships as well as similar excitation temperatures in the case of the Ar‐ICP, the N₂‐MIP, and the N₂‐GDP. It implies that a thermodynamic process such as electron collision would control their excitations. However, only in the case of the ionic‐line plot in the Ar‐GDP, a departure from linear relationship is observed and the estimated excitation temperature is rather higher than that with the atomic lines, meaning that a specific excitation mechanism exists in the Ar‐GDP. A possible explanation for these results is that a charge‐transfer collision between chromium atom and argon ion plays a dominant role in exciting highly‐lying energy levels of chromium ion, especially in the Ar‐GDP.     

Excitation of Doubly‐Charged Ion Emission Lines from a Grimm‐Style Glow Discharge Plasma—Comparison Between Yttrium and Zirconium

Spectra of yttrium and zirconium emitted from a Grimm‐style glow discharge plasma were investigated to elucidate the excitation mechanism of doubly‐charged ionic lines when using argon–helium mixed gas as well as argon gas alone. The energy sum for exciting doubly‐charged ion species of yttrium is slightly smaller compared to the case of zirconium, which yields an interesting correlation in the excitation energy between their ionic species and excited species of helium or argon. The Y III emission lines which were assigned to the 4p⁶5p–4p⁶5s(4p⁶4d) transitions could be observed in the argon–helium mixed gas plasma, but those were hardly excited with argon gas only. The Zr III emission lines did not appear in the spectra emitted by the argon gas plasma nor by the mixed gas plasma. A possible explanation for these phenomena is that the excitation of these ionic species is caused principally by collisional energy transfer from helium species to the analyte atoms.     

Hydrogen and Deuterium Analysis Using Laser‐Induced Plasma Spectroscopy

Abstract

Hydrogen emission in laser plasma has been studied by focusing a TEA CO₂ laser and Nd‐YAG lasers on various types of samples, such as glass, quartz, and zircaloy pipes doped with hydrogen. It was found that H_α emission with a narrow spectral width occurs with high efficiency when the laser plasma is produced in low‐pressure host gas. In contrast, the conventional well‐known laser‐induced breakdown spectroscopy (LIBS), which operates at atmospheric air pressure, cannot be applied for the analysis of hydrogen as impurity. The specific characteristic of hydrogen emission in low‐pressure plasma is interpreted on the basis of our shock wave model, taking account of the fact that the hydrogen mass is extremely light compared to that of the host target. Another experimental study on gas analysis was conducted using an Nd‐YAG laser and helium host gas at atmospheric pressure on a sample of mixed water (H₂O) and heavy water (D₂O) in vapor form. It was shown that completely resolved hydrogen (H_α) and deuterium (D_α) emission lines that are separated by only 0.179 nm could be obtained at a properly delayed detection time when the charged particles responsible for the strong Stark broadening effect in the plasma have mostly disappeared. It is argued that a helium metastable excited state plays the important role in the hydrogen excitation process.     

Measurement of the Stark Broadening of Atomic Emission Lines in Non–Optically Thin Plasmas by Laser‐Induced Breakdown Spectroscopy

We propose a new method for determining the Stark broadening of atomic emission lines using laser‐induced breakdown spectroscopy. The method allows the determination of the Stark broadening in non–optically thin plasmas, through the introduction of a correction for self‐absorption. Couples of lines of the same species are considered. If one of the Stark broadenings is known, the determination of the other does not require the measurement of the electron density of the plasma. Examples are given for the application of the proposed method to the measurement of the Stark broadening of several aluminum emission lines (Al I at 308.2 nm, Al I at 394.4 nm, and Al I at 396.2 nm).     

Mixture of Electromagnetically Induced Transparency and Autler–Townes Splitting in a Five-Level Atomic System

Discerning electromagnetically induced transparency(EIT) from Autler–Townes splitting(ATS) is a significant issue in quantum optics and has attracted wide attention in various three-level configurations. Here we present a detailed study of EIT and ATS in a five-level atomic system considered to be composed of a four-level Y-type subsystem and a three-level Λ-type subsystem. In our theoretical calculations with standard density matrix formalism and steadystate approximation, we obtain the general analytical expression of the first-order matrix element responsible for the probe-field absorption. In light of the well-known three-level EIT and ATS criteria, we numerically show an intersection of EIT with ATS for the Y-type subsystem. Furthermore, we show that an EIT dip is sandwiched between two ATS dips(i.e., multi-dip mixture of EIT and ATS) in the absorption line for the five-level system, which can be explained by the dressed-state theory and Fano interference.     

Determination of the Local Parameters of a Cascade‐Arc Plasma by the Profiles of the Lines in the Radiation Spectrum

The transverse distribution of the plasma temperature in the positive column of a d.c. cascade arc in argon at atmospheric pressure has been measured. The measurements have been carried out by the conventional method involving the determination of the emissivity of plasma as well as directly from the radiation spectrum of the arc without recourse to the Abelian inversion. A theoretical and model justification of the applicability of the second method is given. The results of the determination of the temperature profile in the observation direction by the width and shift of the ArI 425.9nm line selected for the diagnostics are presented. An analysis of the data obtained supports the possibility of determining the temperature of an inhomogeneous, optically thin plasma from the profiles of lines in the emission spectrum.     

Measurement of the Hydrodynamic Efficiency of Laser Plasma at the “Kanal-2” Installation using Aluminum and Copper Targets

The results of experimental measurements of the hydrodynamic efficiency of laser plasma for aluminum and copper targets are presented. The studies were performed on the “Kanal-2” laser setup system using the ballistic pendulum method. The pressure in the interaction chamber was 10^?4 Torr, the pendulum length was 145 mm, the mass of the pendulum with a target was 7.2 g. At the half-height pulse duration of 2.5 ns, the power density on the target surface was ～10¹³ W/cm². In the case of aluminum target, the hydrodynamic efficiency coefficient increased from 1.5% to 4.5% with increasing laser pulse energy from 5 J to 10 J, whereas it remained at the level of 5% for the copper target.     

On the Neutron Yield in the Two-Beam Scheme of Laser Heating and Compression of Spherical Shell Targets with a Low‐Density Coating

At the initial stage of development of large-scale multiple-beam laser facilities for the ignition of the fusion reaction, facilities with a small number of beams is expected to be created. Such facilities are characterized by poor symmetry of irradiation of spherical targets. We have shown that with appropriate design of the target and distribution of the radiation intensity in laser beams the attainment of a neutron yield of 10¹⁵-10¹⁶ is possible even in twoside irradiation of the spherical targets.     

Influence of Spectral Line Deconvolution on Measurement of Excitation Temperature in a Wall‐Stabilized Thermal Plasma by Optical Emission Spectroscopy

Abstract

The measurement of temperature in a wall‐stabilized thermal plasma is done by optical emission spectroscopy. The absolute intensity line method, relative intensity line method, and plot of the Boltzmann function are used. Another method, based on the measurement of electron density and calculations of concentrations, is also used. The influence of spectral line deconvolution on temperature profiles is studied. The results obtained by the four methods are compared. The influence of others parameters, such as the accuracy of spectroscopic constants, and the influence of the theoritical calculations of concentrations are also discussed. These methods employ Ar I, C I and O I lines to measure the temperature of an Ar–CO₂ mixture plasma produced in a wall‐stabilized arc.     

Design and Construction of a Three-Color Gold–Copper-Vapor Laser and the Output-Power Dependence on the Frequency and Buffer-gas Pressure

We design and construct a three-color gold–copper-vapor laser emitting green (510.6 nm), yellow (578.2 nm), and red (627.8 nm) light. The maximum measured total average output power is 12 W under sealed-off conditions. We divide the active medium into three zones (two at both ends for copper and the central zone for gold) in order to vaporize both gold and copper simultaneously. For this purpose, we use a single type of thermal insulator to change the temperature along the medium by varying its thickness, which is the main point in our design. In addition, we carry out some experiments to distinguish the dependence of the output power on the frequency and buffer-gas pressure; the measured ratio of these three wavelengths, green : yellow: red, is 22 : 10 : 7.     

Spectral‐Luminescent Properties of Oxazoles and Oxadiazoles in a Gas Phase on Excitation by Electrons

The energyloss spectra of electrons, fluorescence excitation functions, and the fluorescence spectra on excitation of the vapors of a number of oxazoles and oxadiazoles by monokinetic beams of electrons of various energies are determined. In contrast to optical absorption spectra, in the energyloss spectra of a number of studied substances a band associated with the S ₀–T ₁ singlettriplet transition is observed. The –^*type transitions are fixed up to S ₀–S ₅ on excitation of molecules by highenergy electrons, including the region of vacuum ultraviolet. The cross sections of elastic and inelastic collisions of electrons of different energies with POPOP molecules have been measured. The dependences obtained differ substantially from those calculated in the Born approximation. The cross section of elastic scattering is in a rather good correspondence with the geometric section of the molecule.     

Self—Trapping State and Atomic Tunnelling Current of an Atomic Bose—Einstein Condensate Interacting with a Laser Field in a Double—Well Potential

We present a theoretical treatment of dynamics of an atomic Bose-Einstein condensation interacting with a single-mode quantized travelling-wave laser field in a double-well potential.When the atom-field system is initially in a coherent state,expressions for the energy exchange between atoms and photons are derived.It is revealed that atoms in the two wells can be in a self-trapping state when the tunnelling frequency satisfies two specific conditions,in which the resonant and far off-resonant cases are included.It is found that there is an alternating current with two different sinusoidal oscillations between the two wells,but no dc characteristic of the atomic tunnelling current occurs.It should be emphasized that when without the laser field,both the population difference and the atomic tunnelling current are only a single oscillation.But they will respectively become a superposition of two oscillations with different oscillatory frequencies in the presence of the laser field.For the two oscillations of the population difference,one always has an increment in the oscillatory frequency,the other can have an increment or a decrease under different cases.These conclusions are also suitable to those of the atomic tunnelling current.As a possible application,by measurement of the atomic tunnelling current between the two wells,the number of Bose-condensed atoms can be evaluated.By poperly selecting the laser field,the expected atomic tunnelling current can be obtained too.     

Effect of the Length and Pressure of a Gas Jet on Optical Harmonics Generation by 4.5-μm Femtosecond Laser Radiation of a Fe:ZnSe Laser System

JETP Letters - The effect of the length and pressure of an argon gas jet on low-order harmonics (5th, 7th, 9th, and 11th) generation by 4.5-μm femtosecond laser radiation of a Fe:ZnSe laser...     

Diode Laser‐Excited Optogalvanic and Absorption Measurements of Uranium in a Hollow Cathode Discharge

Optogalvanic spectra for fifty two transition lines of uranium in the wavelength ranges of 662–683, 774–792, and 834–862 nm were measured by using external‐cavity diode lasers. Among these transitions, 860.795 nm and 682.691 nm were chosen for a detailed investigation of the detection limit for uranium by wavelength modulation spectroscopy due to its stronger signal magnitudes. A detection limit of about 2 × 10^? 5 absorbance achieved at 860.795 nm is more sensitive than that obtained at 682.691 nm, but the absorption spectrum at 682.691 nm is preferable to determine the isotope ratio due to the narrower hyperfine structure as well as the larger isotope shift. A preliminary result for an isotope ratio determination in a depleted sample is presented.     

Procedures of Separation and Pre‐concentration for Molybdenum Determination Using Atomic Spectrometry—a Review

Abstract

The literature concerning the improvement of atomic and ionic procedures for molybdenum determination through separation and pre‐concentration were updated. Analytical procedures based on flame atomic absorption spectrometry (AAAS), electrothermal or graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma optical emission spectrometry (ICP‐OES), and inductively coupled plasma mass spectrometry were reviewed taking into consideration the preliminary steps, which can enhance the selectivity and sensitivity based on co‐precipitation, solvent extraction, and solid‐phase extraction. Both in‐batch and on‐line procedures were considered.     

Low Timing Jitter and Tunable Dual-Wavelength Picosecond Pulse Generation from a Fabry--Pérot Laser Diode with External Injection

A novel scheme to generate tunable dual-wavelength optical pulses with low timing jitter at arbitrary repetition rates is proposed and demonstrated experimentally. The pulses are generated from a gain-switched Fabry-Pérot laser diode with two external cw beams for injection seeding simultaneously. The cw light is generated by two independent distributed feedback laser diodes, and their wavelengths can be tuned independently by two temperature controllers. The dual-wavelength pulses with the pulse width of 57 ps, the timing jitter of 340 fs, are obtained. The sidemode-suppression ratio of the output pulses is better than 23dB over a 10-nm wavelength tuning range.     

Dynamics of Thermoluminescence under Dual-Wavelength Vis–IR Laser Excitation of Eosin Molecules in a Polyvinyl Butyral Film Containing Oxygen and Silver Nanoparticles

Optics and Spectroscopy - Electronic and vibrational energy transfer processes taking place in molecular complexes in a polymer are investigated under dual-wavelength (visible at λ = 532 nm...     

Power Density Distribution Simulation and Relevant Heat Effect Calculation of a High-power CO_2 Laser with Low Order Modes

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