Indication of the presence or absence of convective motion in water by nuclear magnetic resonance

Nuclear magnetic resonance was used to determine the characteristic parameters for the evolution of an ensemble of gas bubbles in a liquid exposed to microwave irradiation. These parameters can be used to determine whether convective motion takes place in the liquid. It is observed that a liquid may be “strengthened” by low-intensity radio waves. Pis’ma Zh. Tekh. Fiz. 24, 87–90 (September 26, 1998)     

Ti:Al2O3 laser pumped by radiation from a copper-vapor laser

A scheme enabling spatial matching of copper-vapor laser radiation, which pumps a mode of an Al₂O₃:Ti laser cavity, has been developed and implemented. It is shown that copper vapor lasers as pump sources for titanium-sapphire lasers are fully capable of competing with conventional pump sources. Pis’ma Zh. Tekh. Fiz. 25, 6–11 (September 26, 1999)     

Mesa stripe for the 3–3.6 μm range lasers utilizing gadolinium-doped InAsSbP/InGaAsSb double heterostructures

Data are presented on diode mesa stripe lasers utilizing InAsSbP/InGaAsSb double heterostructures, which are the first long-wavelength lasers to be doped with the rare-earth element gadolinium. It is shown that doping enhances the threshold characteristics. Measurements made of the current modulation of the laser radiation indicate that these lasers may be used in spectroscopic measurements. Pis’ma Zh. Tekh. Fiz. 23, 72–76 (January 12, 1997)     

Scientometric study of laser patent literature

An analysis of the patents filed and scientific papers published and abstracted in theJournal of Current Laser Abstracts (JCLA) for the period 1967–95 indicates that innovative activity in laser science and technology was at its peak in the early 70s. However, scientific activity surpassed the innovative activity in the early 80s. There was a continuous shift in emphasis from “applications of lasers” to “experimental laser research” and to “theoretical laser research”. Further analysis of the 1840 patents field in 1970–71, 1975–76, and 1980–85 indicates that most of the firms filing patents were situated in USA and thus USA is the leading country filing patents in this area followed by Japan. “Spectroscopy of laser output” followed by “Communication applications of laser” got the maximum emphasis.     

Continuous chemical HF laser with a modified radially expanding nozzle unit

We have determined experimentally the energy and spectral characteristics of a supersonic continuous chemical HF laser (oscillator) with a modified radially expanding nozzle unit operating according to the “nozzle–injector–injector” scheme of mixing reactants based on a new method of obtaining oxidizing gas. The practical realization of measures to decrease the heat loss and the loss of fluorine atoms, as well as the optimization of the mode of operation of the modified laser, permitted a 30% increase in its radiation power compared to the base oscillator equipped with a nozzle unit operating according to the “nozzle–injector” mixing scheme. Ways of further enhancement of the energy characteristics of the HF laser radiation are proposed.     

White-light interferometry with depolarization of the radiation

It is shown that the precision of white-light interferometers with a single-mode fiber linking the sensing and processing interferometers can be enhanced by incorporating discrete or all-fiber “time-average” radiation depolarizers (Billings depolarizers). Relations are given to describe the dependence of the output signal and the “ zero” drift of white-light interferometers on the polarization characteristics of the optical channel. Relations are also presented for the elements of the Jones matrix of a Billings depolarizer. Pis’ma Zh. Tekh. Fiz. 23, 56–60 (July 26, 1997)     

“Thermal Prism” Method for Measuring Thermophysical Properties of Thin Films

Theoretical principles underlying the photothermal method for measuring the thickness and thermal properties of a thin film located between two optical elements (“sandwich”) are analyzed. The method is based on the irradiation of the assembly by repetitive pulse laser radiation. Radiation is absorbed in the film and causes heating of the optical elements by heat conduction. The element is monitored by a narrow beam of a second low-power laser propagating through the heated region. The beam is deflected due to the spatial variation of the refractive index, and the magnitude of the deflection angle as a function of time contains the relaxation and “wave” components. It is shown that the phase of the “wave” component depends on the thickness and thermophysical properties of the film. The thermophysical properties of the film can be determined, provided that the analogous properties of the optical element are measured previously or otherwise known, by comparing experimentally measured values of the phase shift with theoretical values obtained from the analytical solution of the non-stationary two-dimensional heat conduction equation.     

In situ TEM measurements of the mechanical properties and behavior of WS2 nanotubes

The mechanical properties of individual WS2 nanotubes were investigated and directly related to their atomic structure details by in situ transmission electron microscope measurements. A brittle mode deformation was observed in bending tests of short (ca. 1 μm in length) multilayer nanotubes. This mode can be related to the atomic structure of their shells. In addition, longer nanotubes (6-7μm in length) were deformed in situ scanning electron microscope, but no plastic deformation was detected. A “sword-in-sheath” fracture mechanism was revealed in tensile loading of a nanotube, and the sliding of inner shells inside the outermost shell was imaged “on-line”. Furthermore, bending modulus of 217 GPa was obtained from measurements of the electric-fieldinduced resonance of these nanotubes.     

Platinum thin films deposited on silicon oxide by focused ion beam: characterization and application

Focused ion beam system was used for deposition of platinum (Pt) thin films on thermally oxidized silicon (Si). Various test patterns (squares and lines) were deposited for electrical characterization of the films, using 2- and 4-terminal measurements. Tests with parallel Pt lines were also carried out, and considerable leakage was detected for the interline distances in the sub-micron range. We investigated two ways to decrease the leakage current: inducing surfaces roughness and using an oxygen plasma after patterns deposition. A method of dielectrophoresis with an AC electric field was applied to align and deposit metallic multi-wall carbon nanotubes (CNT) between pre-fabricated metal, gold, and palladium electrodes with a micron-scale separation. Further, using focused electron and ion beam-deposited Pt contacts in two different configurations (“Pt-on-CNT” and “CNT-on-Pt”), 4-terminal measurements have been performed to evaluate intrinsic nanotube resistances.     

Synthesis of a lithium-encapsulated fullerenol and the effect of the internal lithium cation on its aggregation behavior

A lithium-encapsulated fullerenol Li@C₆₀(OH)₁₈, as an example of a polar solvent-soluble endohedral fullerene derivative, has been synthesized and fully characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy, UV spectroscopy, electron spin resonance (ESR) spectroscopy, matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS), elemental analysis, thermogravimetric analysis, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and the particle size was determined using the induced grating (IG) method, and scanning probe microscopy. The encapsulated Li⁺ was clearly detected by ⁷Li NMR at very high field in the range −15 to −19 ppm, an intermediate lithium-encapsulated fullerenol was detected by MALDI-TOF-MS, and the molar ratio of lithium-encapsulated fullerenol to empty fullerenol was quantitatively determined to be 12:88 by ICP-AES. The solid-state ESR and particle size measurements using the IG method showed the characteristic anionic behavior with no external counter cations, in what can be called a “cation-encapsulated anion nanoparticle”, revealing the drastic differences between its properties and those of empty C₆₀(OH)₁₆.      

Motion of a “drift island” in a toroidal magnetic confinement device with Coulomb scattering of the particles

A resonant drift trajectory of a charged-particle in a magnetic field (a “drift island”) can be used to remove high-energy impurities from a thermonuclear plasma and to introduce (inject) high-energy particles into the plasma. As a rule, these effects are studied neglecting the Coulomb scattering, i.e., in the collisionless approximation. In the present letter, the effect of Coulomb scattering of a particle with a resonant trajectory by plasma particles is studied. The conditions under which the drift resonance is maintained are found, i.e., the plasma densities and plasma density profiles for which the “drift island” can still move over the transverse section of the plasma are determined. Pis’ma Zh. Tekh. Fiz. 25, 19–27 (September 26, 1999)     

“Ecological” transformer-type plasmatron

A mathematical model of a transformer-type induction toroidal discharge is used to determine the gas flow pattern in the cross section of a circular torus. A method of pumping and heating the injected cold gas transverse to the circular axis is proposed. It is concluded that an “ecological” transformer-type plasmatron may be produced. Pis’ma Zh. Tekh. Fiz. 24, 20–24 (April 26, 1998)     

Structure of a weakly ionized gas-discharge plasma

Analysis of the properties of weakly ionized plasmas suggests that strong collective interactions exist in them in spite of the large distance between particles. Arguments supporting this view are presented. First among these is the existence of “hidden” mass, which is observed in experimental measurements of the aerodynamic drag forces. The hidden mass causes an increase in the amplitude of sound waves in a plasma in comparison with an un-ionized gas at identical values of the gas parameters. Analysis of the experimental results shows that gas-discharge plasmas contain previously unknown structural formations that are specific to a plasma and are of a standard type for each species of gas, independent of the pressure and temperature of the plasma. The concentration of particles making up the structure in the plasma of a gas discharge in air is 0.22×10¹⁷ cm⁻³. Pis’ma Zh. Tekh. Fiz. 24, 80–86 (June 12, 1998)     

Influence of heating of the active region in InGaAsP/InP injection lasers on their spectral characteristics

Spectral and spatial characteristics of the output of InGaAsP/InP separate-confinement double heterostructure laser are investigated. The measurements are performed in quasicontinuous and continuous pumping regimes at room temperature. These lasers are shown to be spatially single-mode over the entire working range of currents. The broadening of the longitudinal modes under quasicontinuous pumping is attributed to heating of the active region of the lasers. The pump pulse duration at which heating of the active region of the lasers can be neglected is estimated. Pis’ma Zh. Tekh. Fiz. 25, 88–94 (April 26, 1999)     

Inhomogeneous deformation of crystalline skeleton of syndiotactic polypropylene under uniaxial stretching

Structure changes of syndiotactic polypropylene (sPP) under uniaxial stretching are studied with the combination of micro-tensile tester and in situ wide angle X-ray diffraction (WAXD) measurement. Lamellae stacked “vertically” and “parallel” to the stretching direction (defined as “V” and “P” part) are separated on the basis of two-dimensional WAXD patterns. For all samples with different lamellar thickness, two critical points named as b ₁ and b ₂ were found in the stress–strain curves, while b ₁ and b ₂ points are the onsets of the rotation for the lamellae of “V” part and “P” part, respectively. The corresponding true stress and true strain for b ₂ point are bigger than that of b ₁ , demonstrating that for samples with initial isotropic lamellar orientation, inhomogeneous deformation of crystalline skeleton induced by uniaxial stretching is universal. And after b ₁ point, “stress-induced melting” always occurs simultaneously with lamellar slips. Furthermore, the relationship between lamellar thickness and the true stress for b ₁ and b ₂ point was also studied, illustrating a linear correlation between ln σ and 1/l (σ is the corresponding true stress, l is the lamellar thickness), consistent with Young’s model. However, the critical true strains for these two points did not change with the varying thickness.     

Optically pumped rubidium as a frequency standard at 196 THz

The performance of 196.0-THz (1529-nm) DFB lasers frequency-locked to absorption lines of a rubidium vapor optically pumped at 384.2 THz (780.2 nm) is studied. The absorption profiles of the pumped vapor are measured under various conditions and compared with theoretical predictions. A bright resonance resulting from the cascade of two cycling transitions is characterized both experimentally and theoretically. The measured frequency stability of a DFB laser frequency-locked to this line reaches a level of 2×10^-10 for an averaging time of 100 s when compared to a similar laser locked to an acetylene line     

Broadening of the particle resonance drift trajectory and tritium injection into a fusion reactor with an I=3 helical winding

Two fusion reactor problems, removal of helium ash and fuel (tritium) injection, can be solved using the concept of “drift island motion.” The motion of a drift island is an indicator of the broadening of the resonant trajectory of a charged particle guiding center. This trajectory broadening occurs if two conditions are satisfied. First, the drift pitch angle of the particle is equal to the resonance values i*=n/m, where n and m are the “wave numbers” of the perturbing magnetic field. Second, the drift pitch angle i*=n/m “moves” over the plasma cross section as the particle moves. This displacement is caused by a slow change in the helical magnetic field with time as the particle moves. It is shown that this effect may occur in a fusion reactor with an l=3 helical winding and may be used for tritium ion injection. Pis’ma Zh. Tekh. Fiz. 25, 5–13 (January 26, 1999)     

Possible emission of supermodes in a free electron laser with a transversely developed interaction space

A theoretical analysis is made of the formation of the transverse field profile in a free electron laser with an oversize planar-geometry Bragg cavity driven by a ribbon electron beam. It is shown that cw spatially coherent lasing may be achieved with an oversize parameter of the order of 50 with the excitation of supermodes comprising a set of “ cold” waveguide modes. Pis’ma Zh. Tekh. Fiz. 25, 28–34 (March 12, 1999)     

Determination of the average size and concentration of air bubbles in water by nuclear magnetic resonance

Nuclear magnetic resonance has been used to determine the mean radius of air bubbles in distilled water that has stood for a long time and the volume concentration of these “reduced to mean radius” bubbles. It is shown that the kinetics of the change in the concentration of these bubbles can be observed from the change in the spin-spin relaxation time. Pis’ma Zh. Tekh. Fiz. 23, 42–45 (July 12, 1997)     

Time dependent behavior of elements combining ultra-high performance fiber reinforced concretes (UHPFRC) and reinforced concrete

Structural elements combining Ultra-High Performance Fiber Reinforced Concretes (UHPFRC) and concrete offer a high potential in view of rehabilitation and modification of existing structures. The investigation of the time-dependent behavior of composite “UHPFRC-concrete” elements is a fundamental step in the determination of durability and serviceability. For this, an experimental program was conducted on large composite “UHPFRC-concrete” beams and a numerical model was validated with the test results. The experimental results and a parametric study performed with the numerical model showed that UHPFRC and normal strength reinforced concrete are compatible in the long-term and that the critical period of composite “UHPFRC-concrete” elements are the first 90 days after the casting of the UHPFRC layer. Thus, the high potential of such composite elements can be exploited also in the long term.