Planar optical waveguide temperature sensor based on etched bragg gratings considering nonlinear thermo-optic effect

This paper demonstrates the development of optical temperature sensor based on the etched silica-based planar waveguide Bragg grating. Topics include design and fabrication of the etched planar waveguide Bragg grating optical temperature sensor. The typical bandwidth and reflectivity of the surface etched grating has been ∼0.2 nm and ∼9 %, respectively, at a wavelength of ∼1552 nm. The temperature-induced wavelength change is found to be slightly non-linear over ∼200 °C temperature range. Typically, the temperature-induced fractional Bragg wavelength shift measured in this experiment is 0.0132 nm/°C with linear curve fit. Theoretical models with nonlinear temperature effect for the grating response based on waveguide and plate deformation theories agree with experiments to within acceptable tolerance.     

A method for the formation of ultrathin X-ray beams

It is demonstrated that ultrathin beams with an effective cross sectionh≲100 nm and an angular divergence Δϕ≲2′ below the diffraction limit can be obtained. This is achieved by irradiating the edge of an optically polished face by an X-ray beam with a wavelength of ∼0.1 nm at a grazing angle close to the critical angle of total external reflection and subsequent transmission of the refracted beam through an adjacent side face. Under conditions ensuring effectiveh values of 81 and 96 nm, the values of Δϕ observed experimentally for GaAs and Si samples at wavelengths of 0.154 and 0.139 nm are much smaller than the diffraction limit calculated according to the theory of prism spectrometers. This allows for the formation of an X-ray probe that can be used for local analysis, for example, and layer-by-layer investigations of thin film structures.     

A compact vacuum UV excilamp on argon dimers

The energy and spectral characteristics of the argon dimer emission with the maximum at a wave-length of ∼126 nm under excitation by a pulse-periodic discharge in a gas flow with pressures higher than the atmospheric pressure are studied. A compact excilamp has been designed for obtaining radiation in the vacuum ultraviolet spectrum region. The minimal argon flow velocities are determined, at which cooling is effected by convective gas ejection from the discharge region. This allows one to form a diffusion discharge with a stable radiation power density. It is shown that, when the flow velocity is 0.5 m³/h, the radiation power density of an Ar₂* molecule is >100 μW/cm² behind a LiF window with ∼10% transmission at a wavelength of 126 nm. It is shown that the use of a windowless design and an increase in the gas flow velocity allows an increase in the radiation power density up to 10 mW/cm².     

A silicon position-sensitive detector of charged particles and radiations on the basis of functionally integrated structures with nano-micron active regions

A novel pixel array two-coordinate detector with internal amplification is described. Linear amplification of the primary ionization current is attained by using functionally integrated structures of a p-i-n diode and a bipolar transistor in the detector pixel. It is shown that a 16-fold decrease (from 0.64 to 0.04 μm²) in the emitter area of the functionally integrated structures allows the current gain of pixel bipolar structures to be increased from 10 to 80 at a pixel collector current of ∼1 nA. As a result, it is possible to obtain spectra of radiations weakly interacting with the silicon (e.g., γ rays) and to reduce the response time of the position-sensitive detectors by an order of magnitude, down to 100 ns and less. It is demonstrated that the detector can be used in fast position-sensitive detection of particles with time, coordinate, and energy resolutions of ≤100 ns, ≤25 μm, and ≤12%, respectively.     

A grazing incidence spectrograph for recording spectra in the range of 5–50 nm

A wide-range grazing-incidence spectrograph based on a spherical grating has been developed for recording integrated (over time) line spectra in the region of 5–50 nm. Resolution of the spectrograph λ/Δλ has been determined; at a wavelength of 5 nm, it exceeds 500 units. The spectrograph has been used to analyze line spectra of multiply charged ions for strong resonance lines in the range of 15–20 nm and record the line of X-ray lasing on the 3p-3s transition of a Ne-like Ar ion with wavelength λ = 46.9 nm.     

Measurements of the temperature dependence of optical characteristics of materials in vacuum

A diagnostic module for the experimental analysis of the temperature dependence of spectral reflection coefficients for materials with the use of probing coherent radiation of a laser system with a parametric frequency oscillator (λ ∼ 213–1188 nm) and laser heating of the studied solid-state sample (up to temperatures T ∼ 2500 K) in vacuum is described. The results of the experimental determination of the spectral reflection coefficients are entered into the created partition of the experimental and design-theoretical data base of thermophysical, optical, and transporting properties of structural materials of photon energo-motion and processing high-power-density plants.     

An intermediate-frequency amplifier for a radio-astronomy superheterodyne receiver

Results of designing ultralow-noise coolable amplifiers intended for operation in a 0.5- to 3.0-GHz wavelength range are presented. Schematic diagrams are given, and special features of the design are indicated. The noise factor of the amplifier is ∼0.4 dB without cooling and ≤0.05 dB at 15 K. The commercially available electronic components are used. The amplifiers are recommended as functional modules for building radio-astronomy and measuring units.     

A Spectroscopic refractometer for a 375–1150 nm wavelength range

A spectroscopic refractometer is intended for measuring the index of refraction n _λ of liquid and solid media at any wavelength λ in a 375–1150 nm wavelength range with an accuracy of ±5 × 10⁻⁵. It can be used, in particular, for determining n _λ of monomers, compositions, and polymers, which are used for creating integrated-optical waveguides operating in a telecommunication spectrum region near 850 nm.     

A UV source on hydroxyl molecules operating in a pulsed-periodic mode

The emission and energy characteristics of a UV source based on water vapors, which was excited by a longitudinal pulsed-periodic discharge, are presented. The emission in the spectral range 280–340 nm was studied. The average emission power of gas-discharge plasma of low-pressure (∼130 Pa) water vapors in the UV region was 75 mW.     

Measurements of the zone sensitivity characteristics of photocathodes of fast ϕεy-143 and ϕεy-174 photomultipliers

The results of measurements of zone sensitivity characteristics for photocathodes of fast ϕεy-143 and ϕεy-174 photomultipliers and their spectral sensitivity in a wavelength range of 400–700 nm are presented. An automated setup for measuring photocathode zone characteristics is described.     

Interferometric measurement using bimorph actuated staggered mirror (BASM) microsensor

For physical and chemical sensing applications, a bimorph actuated staggered mirror (BASM) microsensor was designed and fabricated by surface micromachining using a transparent quartz substrate. While the conventional cantilever sensors have angular deflection, BASM’s moving mirror performs piston-type pure vertical motion in response to environmental stimuli like temperature change and surface stress change due to molecular adsorption. Since the sensor itself has a fixed or reference mirror as well as a moving mirror, 1) an interferometric measurement is possible without an additional reference mirror in off-axis measurement setup, and 2) vibration measurement noise can be reduced. For preliminary test purposes, interferometric measurement using an optical setup was performed for temperature change. At He-Ne line (632.8 nm), a temperature change of ∼0.8 K caused a minimum-to-maximum interferometric light intensity change which corresponds to ∼144 nm shift of the moving mirror part. An optical diffraction analysis was performed and optimal device parameters were found to maximize the sensor sensitivity.     

A light-erosion method for high-pressure dust-gas-plasma flows generation

A light-erosion method for generating high-pressure dust-gas-plasma flows during ultraviolet (λ = 213 nm) laser ablation of a polymeric matrix ((C₂F₄) _n ) containing dust particles (thin-wall borosilicate glass microspheres with a ∼15- to 80-μm diameter d) is described. The carrying-out of the dust particles by ionized vapors of the substance of the target matrix, their space-time localization in the gas-plasma flow in a period Δτ ∼ 15–75 μs after the laser exposure up to the further spatial separation of the vaporized substance of the target matrix and the dust particle cloud is recorded by laser interferometry and shadow photography methods. The importance of certain selection of the matrix-dust system for realizing the light-erosion method for generating dust-gas-plasma flows, in particular laser exposure conditions, is shown. When condensed media with a low ionization potential (Al, Ce) are used as a dust component, the proposed method for generating heterogeneous gas-plasma flows can be efficient for their further heating by coherent radiation.     

Mechanical production of tungsten and molybdenum nanoparticles for functional composites

High-purity (∼99.2%) tungsten and molybdenum nanopowders (particle size 30–350 nm) may be obtained by the magnetic-thermal reduction of WO₃ and MoO₃ in conditions of mechanical activation.     

A high-energy YAG: Nd<Superscript>3+</Superscript> laser with a phase conjugation in an optical fiber

An optical scheme and design of a YAG:Nd³⁺ frequency laser with a two-pass amplifier and a mirror with the phase conjugation by the stimulated Brillouin scattering in an optical fiber is described. The maximal radiation energy is 1000 mJ at a 1.064-μm fundamental wavelength and 500, 200, and 20 mJ at the second, fourth, and fifth harmonics, respectively, when the divergence is ∼5 × 10⁻⁴ rad and the pulse duration is 4.5 ns.     

Frictional Voltammetry with Copper

This paper presents an experimental study correlating frictional behavior with in situ voltammetry for a unidirectional sliding contact between a hemispherical tipped alumina probe and a flat rotating copper counterface (maximum Hertzian contact pressure of 68 MPa and sliding speed of 10 mm/s). The contact was immersed in an aqueous 0.1 M Na₂CO₃ solution (pH ∼11) where the copper counterface acted as the working electrode in a potentiostat controlled three-electrode cell; a coiled Pt wire was used as the counter electrode and a saturated calomel electrode (SCE) as the reference. Clear and reproducible trends were found between friction coefficient and published data suggesting the onset of particular redox reactions, graphically presented in a frictional voltammetry plot. At anodic potentials primarily associated with the formation of copper(I) oxide (Cu₂O) (V vs SCE ∼−0.25), the measured friction coefficient was in the range μ ∼0.4–0.5. At cathodic potentials primarily associated with the formation of CuO, Cu(OH)₂, and CuCO₃ (V vs SCE ∼−0.10), the friction coefficient transitions to the range μ ∼0.7–1.0. At sustained cathodic potentials associated with reduction of the native copper oxide, Cu₂O, (V vs SCE ∼−0.65), the friction coefficient is observed to fluctuate between μ ∼0.2 and 0.5, arguably a result of exposure of bare copper due to non-uniform reduction (fractional coverage) of Cu₂O.     

The amplitude and current pulse duration of a supershort avalanche electron beam in air at atmospheric pressure

The results of experimental studies of the parameters (amplitude and duration) of a supershort avalanche electron beam (SAEB) generated in air at atmospheric pressure are presented. It is shown that the pulse duration of the beam current behind the foil from the entire area of the anode foil is larger than from small areas and depends on the cathode design. The number of electrons that are detected behind the 10-μm-thick Al foil is ∼6 × 10¹⁰ electrons, which corresponds to a SAEB amplitude of ∼100 A at a FWHM of the current pulse of ∼100 ps. An X-ray exposure dose per pulse of ∼1.8 mR was obtained using a 20-μm-thick copper foil. It was confirmed that the FWHM of a SAEB pulse is within ∼50 ps from small foil areas (with diameters of ∼7 mm or smaller).     

Characteristics and behavior of the electron beam of the MиH-1 accelerator in air

The electron-beam characteristics of the MиH-1 accelerator have been measured. At the output of the accelerating tube, the current-pulse amplitude is ∼1kA, duration ∼10ns, and maximal electron energy ∼600 keV. As the beam passes through the air, its diameter increases linearly with the distance varying from 2 cm at the tube window to ∼45 cm at a distance of 1 m from it, which agrees with the calculations performed.     

Compositional dependence of the microscopic frictional properties of single crystal metal carbides

The frictional properties of TiC(100), Ti_0.3V_0.6C(100), and VC(100) surfaces in contact with a silicon nitride probe tip have been investigated by atomic force microscopy (AFM) under ambient pressures of dry nitrogen as well as environments of different relative humidities. Calibration of normal and lateral force has permitted the determination of the quantitative frictional properties of the three carbide samples on a nanometer length scale. In these studies, TiC(100) exhibits the lowest friction coefficient, ranging from ∼0.044 to ∼0.082 under the different environments. VC(100) and Ti_0.3V_0.6C(100) have similar friction coefficients (∼0.07) under dry nitrogen conditions, yet VC exhibits a larger friction coefficient (∼0.158) than Ti_0.3V_0.6C (∼0.129) under conditions of higher relative humidity (∼55%). Condensation of water vapor with increasing relative humidity results in an increase in the frictional response for all the three samples. The experimental results demonstrate that the frictional properties of the three carbide samples are correlated to their surface composition and surface free energy.     

An experimental setup for studying neutron-neutron final state interaction on the neutron channel of the Moscow Meson Factory

A setup for measuring the singlet nn-scattering length in the n + d → p + n + n reaction is described. It is composed of a neutron hodoscope with an angular aperture of 12° and a scintillation detector for protons escaping at an angle of 90° with the beam direction. The exit angles and the energies of a proton and both neutrons are measured. The neutron energies are measured using the time-of-flight method. At a time resolution of ∼0.6 ns and a flight base of ∼5.5 m, the accuracy in measuring the neutron energy is ∼1% at an energy of ∼15 MeV. The dependence of the reaction yield on the relative energy of two neutrons is investigated. The neutron-neutron final-state interaction manifests itself as a peak in this distribution.     

Precision processing of CVD diamond plates by Cu-laser irradiation

The chemical vapor deposition (CVD) technique is applied for synthesizing diamond films and plates of large size (∼100 mm) and high quality. In the given work, we consider one of the diamond-structure dimensional processing and microprocessing methods based on the application of a Cu laser, whose irradiation can be focused to a small spot and also used for the intensification of the image brightness in an optical system, which is able to process ∼10⁶ points of an object for one (∼10 ns) or a few pulses. The characteristics of processed surfaces of polycrystalline diamond films and plates are given.