CO<Subscript>2</Subscript> laser oscillating in the range of 16 μm

The ability of a CO₂ laser to oscillate in the range of 16 (14) μm at room temperature was investigated experimentally and theoretically. The output energy per pulse was ~60 mJ at peak power of ~50 kW. It was necessary to minimize not only harmful losses but also useful ones in both channels 00⁰1–02⁰0 and 02⁰0–0110 and to increase the input energy, i.e., the density of free electrons in the discharge, in order to increase the peak power and energy of 16-μm radiation. The highest values of peak power and energy of radiation were reached at different pressures of the active mixture. The rotational bottleneck effect limiting the peak power and energy of oscillation was important at rather low pressures of the active medium. Oscillation at the R12 line is more preferable than that at the P12 line for use as 9.6-μm dumping radiation.     

Generation of 13.9 µm radiation from CO<Subscript>2</Subscript> by cascade lasing or externally applied CO<Subscript>2</Subscript> laser

13.9 μm radiation from the 10⁰0-01¹0 transition can be obtained from a CO₂ laser by saturating the 00⁰1-10⁰0, 10.6 μm transition with an internally generated q-switched pulse or by the application of an external 10.6 μm pulse. Because of Fermi resonance between the symmetric stretch and the bending modes, decay of population from the 10⁰0 level is fast, and such lasers operate at low power and energies. A theoretical model was developed to study such lasers. The results of the calculations indicate that a large-aperture E-beam-sustained discharge is effective for excitation of the cryogenically cooled gain medium, which uses He rich mixture at low pressure. The system is scalable and capable of generating large powers and energies.     

“Cold” CO<Subscript>2</Subscript> laser ablation of green-state LTCC—experimental verification of improved model and comparison of various LTCC materials

New experimental results in support of the universal mechanism of “cold” laser ablation for machining of various commercial green ceramic materials (LTCC) are presented in this paper. The “cold” ablation model was mathematically formulated and employed to derive an ablation curve equation. The model was tested by CO₂ laser ablation of a custom-made green-state alumina ceramic featuring varying binder content. An excellent fit of ablation curve to experimental data was obtained, yielding insight into process energetics and an ablative measurement method of absorption coefficient. The analysis was applied to a sample of commercial LTCC materials. The ablation results were practically identical for all materials in agreement with the prediction of the model, with the high rates of >100 micron/shot at repetition >1 kHz and accuracy comparable with the ceramic grain size. This work provides evidence that the CO₂ laser processing has a great potential to become a key low-cost precision processing method for the existing LTCC-based electronic devices (micro-via drilling, general cutting and scribing) and for the new generation of LTCC-based devices comprising micro-fluidics, micro-mechanics, opto-electronics and meta-material structures.     

Influence of molecular association on the solubility of methylxanthines in supercritical solvent CO<Subscript>2</Subscript>–methanol

Analysis of the experimental data on the solubility of methylxanthines (theophylline and theobromine) in supercritical (SC) solvent CO₂–methanol at various concentrations of methanol within the framework of the ASL model (Associated Solution + Lattice) based on molecular association theory and the simple lattice model is presented. Hetero-association of methylxanthines with the molecules of methanol is studied by means of ¹H NMR spectroscopy at 313 K. The contribution of molecular association to the solubility of methylxanthines in the mixed SC solvent CO₂–methanol is analyzed. It is shown that the presence of NH group in the molecule of methylxanthine, when passing from caffeine to theophylline or theobromine, leads to an increase of the contribution of the component related to molecular association to solubility.     

Solubility of caffeine in the supercritical CO<Subscript>2</Subscript>–methanol binary solvent

The caffeine–methanol association constant at 313 K has been determined by ¹H NMR spectroscopy. The caffeine solubility in the supercritical carbon dioxide (SC-CO₂)–methanol mixed solvent has been calculated using the association constant experimentally measured by NMR in the framework of the associated solution + lattice (ASL) model, which is based on the theory of molecular association and a simple lattice model. Individual contributions to the solubility have been determined, and the relative role of various factors determining the solubility of caffeine in the mixed solvent has been analyzed. The caffeine solubility as a function of the methanol content of the SC-CO₂–methanol system is predicted to pass through a maximum.     

Saturation-dip measurements in the 2ν<Subscript>2</Subscript> overtone band of OCS with a CO<Subscript>2</Subscript>-laser/microwave-sideband spectrometer

We have employed a CO₂-laser/microwave-sideband spectrometer to carry out saturation-dip sub-Doppler measurements of a number of 2₂ overtone transitions of OCS in the 10-m region. The OCS frequencies have been obtained with an absolute accuracy of order ±37 kHz, as determined from a careful analysis of the combined uncertainties in the frequency of our Lamb-dip-locked laser and the centers of the observed OCS saturation signals. Our ±37 kHz measurement accuracy is consistent with literature OCS sub-Doppler data obtained on a similar instrument. The results serve to extend the comb of precise reference frequencies in the 10-m region and to determine the magnitudes of systematic and random uncertainties of our CO₂ laser. PACS 07.57.Ty; 33.20.Ea; 42.62.Fi     

Influence of Matrix Nature on the Structural Characteristics of In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeO<Subscript>2</Subscript> and SnO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> Composites Fabricated by the Impregnation Method

The structural characteristics, valence states, and distribution of cerium ions between the components in In₂O₃–CeO₂ and SnO₂–CeO₂ nanocomposites fabricated using the impregnation method were studied. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) were used to show that, during impregnation, cerium ions are not included into In₂O₃ crystals and are disposed only on their surface in the form of nano-sized crystallites or amorphous clusters. On the other side, under the contact of CeO₂ clusters with a surface of SnO₂ matrix crystals, cerium ions penetrate into the surface layer of these crystals. In contrast to an In₂O₃–CeO₂ system, where the addition of CeO₂ does not affect the conduction activation energy, where cerium oxide is added to SnO₂, the observed increase in the resistance of a SnO₂–CeO₂ composite is accompanied by a sufficient increase in activation energy. These data and the XPS spectra confirm the modification of the surface layers of conductive SnO₂ crystals as, a result of the penetration of cerium ions into these layers.     

Effect of the humidity on the uptake of NO<Subscript>3</Subscript> on coatings composed of MgCl<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O and MgBr<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O and mixtures thereof with NaCl

The reactive uptake of NO₃ radicals on the surface of wetted individual X salts and of wetted X-NaCl salts (X = MgCl₂ · 6H₂O and MgBr₂ · 6H₂O) at [H₂O] = 2 × 10¹²−2 × 10¹⁵ cm⁻³ and NO₃ (4.8 × 10¹² cm⁻³) was studied using a reactor with a movable insert covered with a salt coating in combination with a mass spectrometer for monitoring the initial reactant and products. The probabilities of NO₃ uptake γ on X-NaCl binary salts as functions of the content of doping salt were determined. A parametric approximation of the experimental data was proposed, which makes it possible to quantitatively predict the extent of surface enrichment of a wetted binary salt coating in doping salt and its dependence on the humidity and the content of this salt in the binary mixture. It was established that the relative surface density σ_X of X doping salt depends on its mole fraction μ_X in the X-NaCl binary salt as σ_X = aμ_X (a = 2.2 for MgBr₂ and 13.1 for MgCl₂) over the entire humidity range covered. The contributions of the X salts to the overall uptake of NO₃ at NO₃ concentration typical of the tropospheric conditions ([NO₃] ∼ 10⁷ cm⁻³ and relative humidities of RH ≤ 20%) were estimated.     

Sol–gel synthesis and characterization of Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite solid electrolytes

Composite solid electrolytes in the system (1???x)Li₂CO₃–xAl₂O₃, with x?=?0.0–0.5 (mole), were synthesized by a sol–gel method. The synthesis carried out at low temperature resulted in voluminous and fluffy products. The obtained materials were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy/energy-dispersive X-ray, Fourier transform infrared spectroscopy and AC impedance spectroscopy. Structural analysis of the samples showed an amorphous feature of Li₂CO₃ and traces of α-LiAlO₂, γ-LiAlO₂ and LiAl₅O₈. The prepared composite samples possess high ionic conductivities at 130–180 °C on account of the presence of lithium aluminates as well as the formation of a high concentration of an amorphous phase of Li₂CO₃ via this sol–gel preparative technique.     

Modeling the thermomechanical processes in the output window of a high-power СО<Subscript>2</Subscript> laser

A mathematical model of thermomechanical processes in the output window of a high-power continuous gas laser is developed and used to examine the windows of a СО₂ laser. The dependence of the maximum allowed output radiation power on the beam diameter and the distributions of temperatures and mechanical stresses are obtained, and the divergence of radiation is studied for windows made from ZnSe, KCl, and polycrystalline diamond (PD). In addition, the damage threshold of a composite output window made from PD with a single-crystalline region at the center is considered.     

Specific heat of the [NH<Subscript>2</Subscript>(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>]<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript> crystal in the temperature region 80–300 K

The specific heat of [NH₂(CH₃)₂]₂ZnCl₄ was measured calorimetrically in the temperature region 80–300 K. As the temperature T decreases, the C _p (T) dependence indicates a phase transition sequence, with the phase transition at T₆=151 K observed for the first time. The thermodynamic characteristics of the crystal were refined. The transformation occurring at T₂=298.3 K is shown to be an incommensurate-commensurate phase transition.     

Spin-reorientation phase transition on the surface and in the bulk of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> single crystals

Direct comparison of the properties of a thin surface layer and the bulk of macroscopic hematite (α-Fe₂O₃) crystals was used to study the magnetic structure of the surface layer and the bulk and the processes attendant on spin-reorientation phase transition (SRT). The investigation tool was simultaneous γ-ray, X-ray, and electronic Mössbauer spectroscopy, which enabled us to study the bulk and surface properties of macroscopic samples simultaneously and to compare them directly. Direct evidence of the existence of a surface “transition layer” on hematite crystals is obtained. The existence of this layer was suggested and described by Krinchik and Zubov [JETP 69, 707 (1975)]. The study in the SRT region showed that (1) the Morin SRT in the crystal bulk occurs in a jump (as a first-order phase transition), whereas in the surface layer of about 200 nm thick, some smoothness appears in the mechanism of magnetic-moment reorientation; (2) SRT in the surface layer, as in the bulk, involves an intermediate state in which low-and high-temperature phases coexist; and (3) SRT in the surface layer occurs at a temperature several degrees higher than in the bulk. Our experimental evidence on the SRT mechanism in the surface layer correlates with the inferences from phenomenological theory developed by Kaganov [JETP 79, 1544 (1980)].     

CO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> radicals in synthetic hydroxyapatite

Powders of the B-type synthetic apatite exposed to gamma or ultraviolet irradiation were investigated using EPR spectroscopy. It was shown that ultraviolet irradiation leads to the appearance of the EPR spectrum near g = 2, which is similar to the spectrum observed upon gamma irradiation. The decomposition of the EPR spectra into components and the simulation of the shape of the experimental EPR signals revealed that these signals are associated primarily with two types of CO ₂ ^? radicals, namely, the axial CO ₂ ^? radicals and the orthorhombic CO ₂ ^? radicals. The differences in the shapes of the EPR spectra of the samples exposed to gamma and ultraviolet irradiation were explained by different ratios between the axial and orthorhombic CO ₂ ^? radicals. It was established that thermal annealing results in an increase in the relative contribution to the total EPR spectrum. This increase was explained by the transformation of the orthorhombic radicals into the axial radicals.     

Crossing of the πd<Subscript>5/2</Subscript> and πg<Subscript>7/2</Subscript> orbitals in the <Subscript>51</Subscript>Sb isotopes

Self-consistent calculations using the D1S Gogny force have been performed in order to study the mechanism involved in the crossing of the πd _5/2 and πg _7/2 orbitals in the Sb isotopes. This inversion is well predicted by the HFB + blocking calculations with spherical symmetry performed for the odd-A Sb isotopes. In addition, several HFB and HF calculations have been performed for even-even nuclei of the five neighbouring isotopic chains (Z = 46 to 54, from the proton dripline to N = 82). The results obtained for the binding energies of the two proton orbitals indicate that the radii of the systems play an important role in the crossing, even though some particular πν interactions also give a contribution. The spin-orbit interaction, which is known to be concentrated mainly at the nuclear surface, is proposed to be the main responsible of the crossing.