Study of optical narrow-band N-resonance formed in the vapor of isotope 87Rb atoms in an external magnetic field

Narrow-band cascade N-resonance formed in a Λ-system of rubidium atoms was investigated. Radiation of two continuous narrow-band lasers was used, one of which had a fixed frequency, while the second one was a probe laser. N-resonance may have a sub-natural width and exhibits enhancement of absorption. The behavior of N-resonance in an external magnetic field was examined with use of ⁸⁷Rb atomic vapors.     

Recording of a hologram by using the second-order nonlinearity

The observation of “spatial-modulation” resonances of saturated absorption in the interaction of iodine-127 vapors with a superposition of frequency-nondegenerate TEM₀₁ and TEM₁₀ transverse modes of a linear laser is reported. The modulation of the total radiation power of the probing wave, recorded at twice the beating frequency of transverse modes of the laser, is interpreted to be the result of the transformation of modulation of the spatial distribution of the field into its amplitude modulation under the action of nonlinearly absorbing iodine vapors. Resonances of saturated absorption of the weak line R(127)11-5 of iodine-127 (633 nm) in an extracavity cell are observed by the method proposed.     

On the mechanism of carbon nanotube formation: II. The kinetics of explosive condensation of carbon molten drops in a metallic catalyst

The preliminary stage of the formation of carbon nanotubes by the vapor-liquid-drop mechanism is considered as applied to the condensation of drops from carbon and metal vapors. The problem of the condensation of molten drops is solved for a wide concentration range for both vapors at a condensation temperature. It is shown that, at very high concentrations of the metal vapor (10¹⁸–10¹⁹ cm⁻³) and high temperatures (about 0.3 eV), peculiar heterogeneous condensation of the drops can occur at huge supersaturation of the carbon vapor and the saturated metal vapor. This problem of the condensation of the binary vapor is of methodical interest. This condensation is shown to be unrealizable in real experiment at the parameters of the carbon and metal vapors; it virtually merges with the homogeneous condensation of the metal vapor. The maximum concentration of the carbon vapor below which carbon condenses into drops and above which carbon condenses into amorphous soot particles is calculated. The calculation makes it possible to propose a new approach to the controlled growth of carbon nanotubes.     

Effect of the pump absorption on generation of infrared stimulated electronic Raman scattering in alkali-metal vapors

The main properties of infrared stimulated electronic Raman scattering (SERS) at the 6² S _1/2-7² S _{1/2, 3/2} transitions in cesium atoms are studied theoretically and experimentally as functions of the atomic concentration, which was varied from 10¹¹ to 10¹⁶ cm^?3. It is found that the efficiency of generation of Stokes radiation strongly depends on one-photon absorption of the pump radiation tuned near frequencies of the 6² S _1/2-7² P _{1/2, 3/2} transitions. By using the equation for the density matrix, which describes the evolution of a three-level system, the theory of resonance excitation of IR radiation upon one-photon absorption at an adjacent transition is developed. The theory describes well the main features of IR SERS in alkali-metal vapors.     

KCs Molecular Bands in the Visible Region

Optics and Spectroscopy - We measured light absorption of potassium and cesium mixed vapors at temperatures 360–660°C in the visible spectral region 380–780 nm. By comparison with...     

Nonlinear transmittance of ZnSe:Fe<Superscript>2+</Superscript> crystal at a wavelength of 2.92 μm

ZnSe crystals doped with Fe²⁺ ions are produced with the diffusion method under the conditions for thermodynamic equilibrium of solid ZnSe, solid Fe, and vapors (S_ZnSe-S_Fe-V). The transmittance of the samples is varied from 7 to 50% (in the absence of the antireflection coating) for a wavelength of about 3 μm. It is demonstrated that the transmittance of the ZnSe:Fe²⁺ crystals increases with an increase in the energy density of the high-power laser radiation with a wavelength of 2.92 μm. An equation that describes the propagation of the resonant radiation in a medium with saturable absorption at an arbitrary ratio of the radiation pulse duration to the relaxation time of the medium is introduced for the analysis of the experimental dependence of the transmittance on the energy density.     

Infrared spectroscopy of a dense potassium vapor jet

In this paper we report the development of new apparatus for the containment and study of dense alkali metal vapors, and the use of the apparatus to study the infrared spectra of potassium vapor. The apparatus is the first to employ aerodynamic confinement of a dense alkali vapor. We have recorded absorption spectra, thermal emission spectra, and laser-induced emission spectra of dense potassium vapor. These techniques all reveal a spectral feature near 1.1 μm which we believe originates in ³Σ⁺_g→³Σ⁺_u transitions of the K₂ molecule.     

Selective response of DPPV/zeolite composites toward acetone,methanol, and n-heptane vapors

In this work, doped poly(p-phenylene vinylene)/zeolite composites was prepared to detect the three different chemical vapors (acetone, methanol, and n-heptane) and to investigate the effects of zeolite type, chemical vapor type, and vapor concentration based on the electrical conductivity response and selectivity properties of the sensing materials. Before blending with PPV, zeolite Y (Si/Al?=?5.1 and Na⁺), mordenite (Si/Al?=?18 and Na⁺), and 5A (LTA) (Si/Al?=?1.0 and Na⁺) were ion exchanged with Cu²⁺ at 80 % ion exchanged to prepare 80CuNaY, 80CuNaMOR, and 80CuNa5A. 80CuNaY exhibited the highest electrical conductivity response under acetone and methanol exposures while 80CuNaMOR showed the highest response in n-heptane exposure which depended on the adsorption and solubility properties of each porous material. When adding doped poly(p-phenylene vinylene) (dPPV) into the 80CuNaY matrix, the minimum detection vapor concentration decreased in acetone, methanol, and n-heptane vapors. For the selectivity, the composite between 80CuNaY and dPPV responded only in the polar vapors (acetone, methanol) whereas the composite between dPPV and 80CuNaMOR or dPPV_[90]80CuNaMOR responded only in the nonpolar vapor (n-heptane). The interactions between the sensing materials and the chemical vapors were investigated and identified by FTIR and AFM techniques.     

Insight of arsenic transformation behavior during high-arsenic coal combustion

The release of arsenic vapors (As³⁺) during high-arsenic coal combustion not only raises serious environmental concerns, but also causes catalyst deactivation in selective catalytic reduction (SCR) systems. To illuminate the mechanisms involved in the transformation of arsenic vapors towards less troublesome arsenates (As⁵⁺) during coal combustion, the accessory minerals in the high-arsenic coal were identified and the association relationship of these compounds with arsenic in fly ash was estimated. The results showed that Si/Al were the main inorganic elements in high-arsenic coal while the content of Ca was quite low. Ca was mostly transformed into sulfates during coal combustion and the effect of Ca on the arsenic transformation was limited. Al/Fe played a more significant role in arsenic speciation transformation and arsenic in the fly ash was predominantly bound with Al/Fe-oxides as arsenates. It was further confirmed that Al in kaolin/metakaolin showed good capacity on arsenic capture. In addition, few arsenic vapors were captured through the physical adsorption mechanism and the large fraction of As³⁺ in some fine particles was mostly attributed to the chemical reactions between arsenic vapors and Al-compounds. Meanwhile, a certain amount of arsenic vapors were converted into As₂O₅(s) under the influence of SCR catalyst and then carried by flue gas to participate in fly ash. Besides, part of arsenic distributed in the fly ash was through the stabilization of ash matrix in high temperature conditions. The transformation of arsenic from vapors towards particulate arsenic favored arsenic emission control by particulate matter control devices.     

Determination of copper content in soils and ores by laser-induced breakdown spectrometry

Features of electromagnetically induced transparency (EIT) in potassium vapors at the D₁ line of the ³⁹K isotope are studied. EIT resonances with a subnatural width of 3.5 MHz have been recorded upon excitation by two independent narrow-band diode lasers in a 1-cm-long cell filled with a natural mixture of potassium isotopes and buffer gas. The splitting of EIT resonances in potassium vapors in longitudinal and transverse magnetic fields has been studied for the first time. The splitted components also have a subnatural width. The smallness of the coupling factor of the hyperfine structure in ³⁹K atoms leads to a transition to the Paschen—Back regime at relatively weaker magnetic fields than in the case of Cs, Rb, and Na atoms. Practical applications of the phenomena under study are noted. The theoretical model well explains the experiment.     

Stepwise ionization of the 2,4-dioxybenzaldehyde and 3,4-dimethoxypropiophenone vapors

The processes of stepwise ionization of the 2,4-dioxybenzaldehyde and 3,4-dimethoxypropiophenone vapors by radiation in the range of wavelengths down to 266 nm were studied using total-current spectroscopy, mass spectrometry, and photoelectron spectroscopy. The process of two-step ionization and the resulting generation of molecular ions are dominant if the laser-radiation intensity amounts to ≈10⁶ W/cm². These molecular ions have appreciable (up to 1.8 eV) energy of vibrational excitation. As the laser-radiation intensity increases, progressively more pronounced fragmentation occurs owing to dissociation of molecular (and, possibly, fragmentation) ions as a result of absorption of at least a single additional photon. The processes leading to fragmentation of ions are suggested. It is found that the dissociation-ionization mechanism is important for the dimethoxypropiophenone. Dissociation with a breakage of the α bond in the carbonyl group with subsequent two-photon ionization of the fragments occurs when the S ₂(¹ A′) state of the ππ* type is excited.     

Generation of coherent radiation at 89.6 nm through two-photon resonant phase-matched tripling of fourth-harmonic Nd: Glass laser radiation in Hg vapors

Coherent radiation at 89.6 nm has been obtained through third-harmonic conversion of the 268.8 nm pulses in mercury vapors. Tunability of the fourth-harmonic frequency of the Nd: glass laser radiation to the 6s ¹ S ₀–8s ¹ S ₀ double quantum resonance of Hg atoms has been used for the resonant enhancement of the twelfth-harmonic output. Possibility to phase match the generated radiation and driving polarisation in pure vapors without employing of bufer gas has been demonstrated.     

Quantum–Chemical Studies on the Superposition of Absorption Bands in the Carbonyl Region of the IR Spectra of Acetylacetone

Using the MO LCAO SCF method in the PM3 approximation, we have investigated the influence of various internal motions of the enol molecule of acetylacetone on the harmonic vibrational frequencies of the C=O and C=C groups. The results of the investigation are discussed with reference to the available literature data on vibrational spectra of acetylacetone and its substituted derivatives. They suggest that the nature of the wide intense IR band 1620 cm^–1 in the spectra of acetylacetone vapors responsible for the absorption of its enol double bonds and its temperature dependence are determined by the tunnel mechanism of enol proton motion in the H–bond channel, the probability of whose realization is controlled by the internal rotation of methyl substituents.     

Studying the regime of complete decoupling of the bond between the electron and nuclear moments at the <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript>-line of the <Superscript>39</Superscript>K potassium isotope using a spectroscopic microcell

Atomic transitions of the ³⁹K potassium isotope in strong (up to 1 kG) longitudinal and transverse magnetic fields have been studied with a high spectral resolution. It has been shown that crossover resonances are almost absent in the saturated absorption spectrum of potassium vapors in a 30-μm-thick microcell. This, together with the small spectral width of atomic transitions (~30 MHz), allows one to use the saturated absorption spectrum for determining frequencies and probabilities of individual transitions. Among the alkali metals, potassium atoms have the smallest magnitude of the hyperfine splitting of the lower level. This allows one to observe the break of the coupling between the electronic and nuclear angular momentums at comparatively low magnetic fields B > 500 G, i.e., to implement the hyperfine Paschen–Back regime (HPB). In the HPB regime, four equidistantly positioned transitions with the same amplitude are detected in circularly polarized light (σ⁺). In linearly polarized light (π) at the transverse orientation of the magnetic field, the spectrum consists of eight lines which are grouped in two groups each of which consists of four lines. Each group has a special distinguished G-transition and the transition that is forbidden in the zero magnetic field. In the HPB regime, the probabilities of transitions in a group and derivatives of their frequency shifts with respect to the magnetic field asymptotically tend to magnitudes that are typical for the aforesaid distinguished G-transition. Some practical applications for the used microcell are mentioned.     

Electric conductivity of siliconorganic polyhomoconjugated polymer films upon adsorption of volatile organic compounds

The electrophysical parameters of polyhomoconjugated organosilicon polymer films are studied, and variation of their conductivity under the action of water, toluene, and ammonia vapors is measured. Films 1–2 μm thick are prepared by the casting method from a solution of poly[2,2-dimethyl-2-sila-1,3-propylene-(4, 4′-biphenylene)]a (polymer I) and poly[2-n -butyl-2-phenyl-2-sila-1,3-propylene-(4, 4′-biphenylene)]a (polymer II). In the course of conductivity measurement, organic volatiles and water are adsorbed due to a stepwise rise in the pressure over the sample from 10⁻³ to 10⁻¹ Torr. The initial values of the resistivity of polymers I and II are estimated as 4 × 10⁹ Θ cm. Exposure of the films to organic volatile vapors and water vapor causes a reversible change in the conductivity of the films. For polymer-I films, the conductivity upon adsorption of ammonia, toluene, and water vapors exceeds the initial value by 150, 10, and 600 times, respectively. The sensitivity of polymer-II films is lower by a factor of 1.5–2.0. The time of conductivity variation as the vapors are injected and evacuated is within 10 and 30 s, respectively. The mechanisms of organic volatile and water adsorption on the surface of polyhomoconjugated organosilicon polymer films are compared with adsorption mechanisms on the surface of π-polyconjugated organic films.     

Equilibrium charge-state fractions for 2.7–31 keV deuterium atoms and ions in strontium vapor

Equilibrium charge-state fractions of 2.7–31 keV deuterium in strontium vapor are reported. The energy dependence of the D^- equilibrium yield is discussed. The results are compared with the D^- yield in cesium and magnesium vapors.     

On the mechanism of formation and broadening of the electronic and vibrational spectra of vapors of octaethylporphyrin metal complexes

Optical absorption spectra of vapors of metal complexes of octaethylporphyrins known from the literature are analyzed on the basis of notions about sequences as basic elements of the formation of electronic-vibrational bands. According to this analysis, major features of these spectra are explained. These features include considerable half-widths of the electronic-vibrational bands of rarefied vapors, when intermolecular interactions virtually do not affect the broadening; a Lorentzian intensity distribution over the contour of the 0-0 spectral band; long-wavelength shifts of the intensity maxima of bands with increasing temperature; and the origin of a fine structure of the electronic and vibrational spectra at low temperatures. It was concluded that sequential transitions form the basis of the mechanism of formation and broadening of the electronic and vibrational spectra of metal complexes of octaethylporphyrins as representatives of complex biomolecules.     

Correlations between vapor-phase Na/K/As adsorption capacities of kaolinite and temperature-dependent derivation of its Al-containing groups

Kaolinite is a commonly used additive, which has been proven to be capable of in-furnace capturing the vapor-phase Na, K, and As, so as to alleviate the fouling and slagging on the heat-exchange surface, the poisoning of selective catalytic reduction (SCR) catalyst, and to reduce related environmental pollution. Considering that temperature-dependent derivation of kaolinites significantly influence the collaborative removal of these vapors, the present study quantified the Na/K/As adsorption capacity of kaolinites using a self-designed device over a wide temperature range to explore the temperature window for high adsorption efficiency. By analyzing Al-coordination of kaolinites before and after adsorption, fixation pathway of Na/K/As vapor was revealed. Effect analysis of single adsorbed atom combined with adsorption energy calculation based on density functional theory (DFT) was performed to demonstrate the difference of adsorption sites for Na/K/As vapors. The results showed that kaolinites had high Na/K/As adsorption capacity at 1073 K–1173 K, 723 K–1273 K, and 1173 K, respectively. When the temperature was between 723 K and 1173 K, the primary hexa-coordinated ^[VI]Al of kaolinites transformed into penta-coordinated ^[V]Al/tetra-coordinated ^[IV]Al. The newly formed ^[IV]Al atoms bonded with Na/K/As atoms. Specifically, both of center sites and bridge sites of ^[IV]Al-O rings can offer position for the fixation of Na and K atoms, and Na atoms were prone to be fixed at the former sites, while K atoms were easy to locate at the latter. In contrast, almost only the center sites of ^[IV]Al-O rings contributed to As adsorption. Thus, with the segmented injection of kaolinites at different temperature within 723 K–1273 K, development of two kinds of modified kaolinites with more center sites or bridge sites of ^[IV]Al–O rings were recommended to avoid competitive adsorption and realize collaborative removal of Na/K/As vapors.     

About the Zeeman Light-Induced Frequency Shift of the Radio-Optical Resonance in Optically Oriented Isotopes of Alkali Metals

Results of calculations of tensor and vector components of the light-induced frequency shift of the radio-optical resonance in optically oriented potassium, rubidium, and cesium vapors are presented. The feasibility of cancellation of the tensor and vector components by the proper choice of the sign of pump light polarization is demonstrated. The influence of buffer inert argon and helium gases on the Zeeman light-induced shift of the resonant frequency in the unresolved radio-frequency absorption spectrum of rubidium-87 vapors is studied.     

Optical pumping of cesium atoms with second resonance light

We report the first successful optical pumping of cesium atoms to a state of high spin polarization with a CW dye laser tuned to the D₁ second resonance line (4593 Å) of the cesium atom. Results of spin polarization versus laser power measurements for cells containing high-density cesium vapors (10¹³–10¹⁵ cm^-3) plus mixtures of nitrogen (10–200 torr) and helium (≈1 atmosphere) gases are presented. These experiments have revealed unexpected limits to the spin polarization of dense alkali vapors.