Reconstructing parameters of sediment layers of a shallow sea bottom using broadband seismoacoustic sources

We study the possibilities of reconstructings the parameters of the sediment layers of a shallow sea bottom from interference patterns appearing during sounding of the bottom by broadband seismoacoustic sources with a bistatic sea-bottom sounding scheme, adaptive signal reception with a horizontal array, and matched filtration of low-frequency seismoacoustic pulses excited with an air gun and interacting with the sea bottom, as well as seismoacoustic noise from a vessel in a shallow sea. The parameters of sediment layers of the sea bottom are reconstructed by statistical checking of hypotheses on the parameters of dynamic spectra obtained by parametric models. Comparative possibilities of reconstructing sea bottom parameters with bistatic and monostatic observation schemes are discussed.     

Monitoring of anthropogenic noise on the shelf of Sakhalin Island during seismic survey research

The paper describes the technique and gives the results of acoustic-noise and seismoacoustic-signal-parameter measurements on a northeast shelf of Sakhalin Island, generated during seismoacoustic research at the licensed Chaivinskii site. The aim of measurements was acoustic control of the water area round an emitting vessel. Results of field measurements and 3-D simulations of seismoacoustic signal propagations on sea and land are presented.     

Seismoacoustic survey of artificial inhomogeneities in the ground

The results of processing the field test data obtained for the seismoacoustic system designed at the Institute of Applied Physics of the Russian Academy of Sciences for the visualization of underground engineering structures are presented. The described experiment is the first demonstration of the use of a high-power, high-stability transmitting-receiving system for producing a coherent insonification with a frequency of 195 Hz. The receiving element of the system is a synthetic aperture array. With the use of focusing as a method of the final signal processing, an image of a tunnel lying at a depth of 30 m is obtained in three spatial cross-sections, which demonstrates the possibility of a three-dimensional, coherent, high-frequency seismic survey of engineering structures.     

Long-base fiber-optic deformometer for the measurement of linear deformations

Principles of a fiber-optic measurement system for the monitoring of seismoacoustic and deformation processes in large-scale physical objects and technical constructions are developed. The system is based on a low-mode fiber-optic interferometer that is sensitive to linear deformations.     

Surface-to-volume wave conversion in shallow water with a corrugated bottom

Acoustic transmission between points onshore or in very shallow water and points in deep water is strongly influenced by the shear rigidity of marine sediments, which control the parameters and the very existence of seismoacoustic surface waves. Previously, it was found that coupling between acoustic modes and the seismoacoustic surface waves is normally weak, although not negligible in the case of a gently sloping seafloor and soft sediments. In this paper, the previous work is extended by accounting for the small-scale roughness of the seafloor. The significant role of roughness in coupling between volume and surface waves is demonstrated. The combined effect of bottom topography, roughness, and wave attenuation in soft marine sediments on the sound propagation between points in shallow and deep water is discussed. Published in Russian in Akusticheskiĭ Zhurnal, 2008, Vol. 54, No. 3, pp. 400–407. The article was translated by the author.     

Excitation of seismoacoustic waves by a harmonic force source acting at the boundary of a liquid layer and an elastic halfspace

A problem on the excitation of seismoacoustic waves in a system of a homogeneous isotropic elastic halfspace covered with a liquid layer is solved in the case of action of a source of point harmonic force on the surface of an elastic medium. Integral expressions are obtained for the radiation powers averaged over a wave period for longitudinal and transverse waves in a solid. Mode excitation is analyzed in detail. Expressions describing parts of the mode powers radiated into a liquid layer and an elastic medium are obtained. Numerical analysis of radiation powers is conducted for spherical longitudinal and transverse waves as well as for the radiation powers of seismoacoustic modes in a solid halfspace and a liquid layer. It is determined that in the conditions characteristic of bottom rocks in the case, where the basin depth is several times and more larger than the sound’s wavelength, about 2/3 of the total power is radiated into a liquid.     

Development of a nuclear spin polarizer with the optical pumping method

We have developed an optical pumping NMR system for semiconductors as an effective nuclear spin polarizer for a solid-state NMR quantum computer. The system was successfully applied to enhance ³¹P nuclear spin polarization in InP doped with Fe, and the enhancement of the ³¹P NMR signal by more than two orders of magnitude was achieved. We also observed the strong dependences of the enhancement on the helicity and the photon energy of incident light. The most effective enhancement was achieved with the helicity σ⁺ and photon energy smaller than the bandgap by 1015 meV.     

Surface-to-volume wave conversion in shallow water with a gently sloping bottom

Marine sediments support seismoacoustic surface waves, which can propagate along the seafloor, in deep and shallow water, and even onshore. Because of the strong attenuation of compressional and especially shear waves in the sediments, the surface waves can significantly contribute to the acoustic field far from the shore only through their coupling with volume waves in the water. We theoretically study the excitation of acoustic normal modes by seismoacoustic surface waves in a shallow-water waveguide with a sloping bottom consisting of unconsolidated marine sediments. It is found that the coupling primarily occurs in the vicinity of a modal cutoff. The effects of geoacoustic parameters and stratification of soft marine sediments on the efficiency of surface-to-volume conversion are investigated. Published in Russian in Akusticheskiĭ Zhurnal, 2007, Vol. 53, No. 6, pp. 809–816. The article was translated by the author.     

Development of injection-seeded, pulsed optical parametric generator/oscillator systems for high-resolution spectroscopy

We report the development and application of pulsed optical parametric generator (OPG) and optical parametric oscillator (OPO) systems that are injection seeded with near-infrared distributed feedback diode lasers. The OPG is injection seeded at the idler wavelength without the use of a resonant cavity. Two counter-rotating, beta-barium-borate (β-BBO) crystals are used in the OPG. These crystals are pumped by the third harmonic, 355-nm output of an injection-seeded Nd:YAG laser. An OPO version of the system has also been developed by placing two flat mirrors around the two β-BBO crystals to form a feedback cavity at the signal wavelength. The OPO cavity length is not actively controlled. The output signal beam from the OPG or OPO is amplified using an optical parametric amplifier (OPA) stage with four β-BBO crystals. The frequency bandwidths of the signal and idler laser radiation from OPG/OPA and OPO/OPA systems have been determined to be slightly greater than 200 MHz. The temporal pulses from each system are smooth and near-Gaussian. High-resolution optical absorption measurements of acetylene (C₂H₂) were performed as another check of the frequency spectrum of the idler beam. The frequency-doubled signal output of the OPO/OPA system was used to perform high-resolution, single-photon, laser-induced fluorescence (LIF) spectroscopic studies of the (0,0) vibrational band of the A ²Σ⁺−X ²Π electronic transition of nitric oxide (NO) at low pressure. Excellent agreement was obtained between the theory and the experiment. The signal output of the OPG/OPA system was also used for sub-Doppler, two-photon LIF spectroscopic studies of the same vibration–rotation manifold of NO.This revised version was published online in August 2005 with a corrected cover date.     

Monitoring of spectroscopic changes of a single trapped fission yeast cell by using a Raman tweezers set-up

We demonstrate an improvement of the sensitivity of a Raman tweezers set-up, which combines optical tweezers with Raman spectroscopy. The system was tested by taking the Raman spectrum of a 4.6 μm diameter polystyrene sphere trapped in an aqueous solution. The improvement of sensitivity of the set-up was achieved by adjusting the trap depth for maximum signal to noise ratio (SNR). The maximum SNR was obtained by investigating the Raman peak of a trapped polystyrene sphere at 1001 cm⁻¹ according to trap depth. With this system, a single trapped living Schizosaccharomyces Pombe yeast cell was sensitively monitored by taking the kinetic Raman spectra for more than 2 h. The relative intensity decrease in amide I and amide III bands, frequency increase in amide I band together with alterations in tyrosine marker band around 850 cm⁻¹ was observed, which indicates alterations in the hydration state of protein by time progressing.     

A Rb-magnetometer for a wide range and high sensitivity

A Rb-magnetometer was constructed for a wide range of application. It uses a very small optically pumped resonance cell with an active volume of less than 0.1 cm³ as the sensor element. The cell is housed in a small probe containing polarizer, rf-coil, heater and photoelement. The pumping light is brought to the resonance cell by use of a 3 m long fibre optics. The magnetometer allows continuous monitoring or stabilizing magnetic fields from about 3·10^?8T to beyond 0.3T. The ultimate sensitivity of the instrument is of the order of 10^?10T. Observing the Hanle signal in the transverse mode of optical pumping the instrument can be used for zero field detection and for the measurement for weak fields by means of field compensation.     

A data acquisition system based on digital signal processors for a setup with the detecting of coincident events

A setup is described for detecting several charged and neutral particles in coincidence and determining their energy and time parameters. The CAEN DT5742 (DT5720) desktop digitizer based on a digital signal processor is chosen as a central element of the data acquisition system. Using measurements of the parameters of secondary particles in the d + ²H → ²He + ²n reaction as an example, it is shown that this configuration allows all necessary information to be collected using a minimal set of electronic units, while the processing of digitized signals offers broad opportunities for interpreting the obtained data.     

Frequency stabilization of a diode laser using electromagnetically induced transparency in a V-configuration cesium atom

An electromagnetically induced transparency (EIT) signal is observed in a V-type energy level scheme in a cesium vapor cell at room temperature. The effects of frequency detuning and the intensity of the pump laser on the EIT signal have been investigated. The performance of the probe-diode laser system, which is frequency stabilized on the EIT signal by using electrical feedback, is explored. The first derivative of the EIT signal offers a steeper slope and better S/N ratio for laser frequency stabilization than that of the Doppler-free hyperfine and crossover resonances. A comparative study of the frequency stability of an external-cavity diode laser stabilized at EIT and at the crossover resonance is presented. The square root of the Allan variance (σ) vs. integration time (τ) plot shows about a tenfold improvement in the frequency stability of the EIT-locked laser (σ ～ 2.043 × 10^?13τ^?1/2) over that of the crossover-locked laser under a short integration time (1–10 ms), whereas a twofold improvement is found under a long integration time (～1 s).     

Development of Very-Low-Temperature Millimeter-Wave Electron-Spin-Resonance Measurement System

We report the development of a millimeter-wave electron-spin-resonance (ESR) measurement system at the University of Fukui using a ³He/⁴He dilution refrigerator to reach temperatures below 1 K. The system operates in the frequency range of 125–130 GHz, with a homodyne detection. A nuclear-magnetic-resonance (NMR) measurement system was also developed in this system as the extension for millimeter-wave ESR/NMR double magnetic-resonance (DoMR) experiments. Several types of Fabry–Pérot-type resonators (FPR) have been developed: A piezo actuator attached to an FPR enables an electric tuning of cavity frequency. A flat mirror of an FPR has been fabricated using a gold thin film aiming for DoMR. ESR signal was measured down to 0.09 K. Results of ESR measurements of an organic radical crystal and phosphorous-doped silicon are presented. The NMR signal from ¹H contained in the resonator is also detected successfully as a test for DoMR.     

Optical response of a cold-electron bolometer array

A multielement bolometric receiver system has been developed to measure the power and polarization of radiation at a calculated frequency of 345 GHz. Arrays of ten series-parallel connected cold-electron bolometers have been pairwise integrated into orthogonal ports of a cross-slot antenna. Arrays are connected in parallel in the high-frequency input signal and in series in the output signal, which is measured at a low frequency, and in a dc bias. Such an array makes it possible to increase the output resistance by two orders of magnitude as compared to an individual bolometer under the same conditions of high-frequency matching and to optimize the matching with the JFET amplifier impedance up to dozens of megohms. Parallel connection ensures matching of the input signal to the cross-slot antenna with an impedance of 30 Ω on a massive silicon dielectric lens. At a temperature of 100 mK, a response to the thermal radiation of a thermal radiation source with an emissivity of 0.3, which covers the input aperture of the antenna and is heated to 3 K, is 25 μV/K. Taking into account real noise, the optical fluctuation dc sensitivity is 5 mK, the estimated sensitivity corresponding to the noise of the amplifier is about 10⁻⁴ K/Hz^1/2, and the noise-equivalent power is about (1–5) × 10⁻¹⁷ W/Hz^1/2.     

High-power,high-quality ZGP OPO pumped by a Tm,Ho:GdVO<Subscript>4</Subscript> laser

We report a ZGP OPO system capable of producing >6 W at a signal wavelength of 3.80 μm and an idler wavelength of 4.45 μm. The pumping source is the Tm,Ho:GdVO₄ laser operated at 2.049 μm with an M ² of 1.07. The ZGP OPO generated a total combined output power of 6.1 W at signal wavelength and idler wavelength under pumping power of 18.3 W, and an M ² of 1.7 for OPO output was obtained.     

Information propagation from IP3 to target protein: A combined model for encoding and decoding of Ca signal

It is well known that information is encoded in the frequency or amplitude of Ca²⁺ signal and then decoded by target protein. However, few models considered both the encoding and decoding procedures of Ca²⁺ signal. In this work, a minimal Li-Rinzel model is coupled with a phosphorylation-dephosphorylation cycle model, which is used to investigate information transmissions from inositol 1,4,5-trisphosphate (IP₃) to target proteins and their relations. We found that the mean target protein activity increases with the IP₃ concentration, and at a low level of stimulation, the target protein can be more efficiently activated by an oscillatory signal than a constant signal of the same average calcium if Ca²⁺ acts cooperatively on the kinase. The internal noise resulting from the finite system size is also taken into account in the combined model.     

An ultra-stable referenced interrogation system in the deep ultraviolet for a mercury optical lattice clock

We have developed an ultra-stable source in the deep ultraviolet, suitable to fulfil the interrogation requirements of a future fully-operational lattice clock based on neutral mercury. At the core of the system is a Fabry–Pérot cavity which is highly impervious to temperature and vibrational perturbations. The mirror substrate is made of fused silica in order to exploit the comparatively low thermal noise limits associated with this material. By stabilizing the frequency of a 1062.6 nm Yb-doped fiber laser to the cavity, and including an additional link to LNE-SYRTE’s fountain primary frequency standards via an optical frequency comb, we produce a signal which is both stable at the 10^?15 level in fractional terms and referenced to primary frequency standards. The signal is subsequently amplified and frequency-doubled twice to produce several milliwatts of interrogation signal at 265.6 nm in the deep ultraviolet.     

Gas-temperature imaging in a low-pressure flame reactor for nano-particle synthesis with multi-line NO-LIF thermometry

Multi-line NO-LIF temperature imaging was applied to measure two-dimensional gas-temperature fields in a low-pressure, premixed flat-flame nano-particle generator during nano-particles synthesis. It was the first time that this calibration-free technique was applied in a low-pressure combustion system. The laser fluence was limited to 4 kW/cm² in order to avoid saturation of the LIF signal, which influences the temperature results. While minimizing the elastically scattered light, the efficiency of the LIF detection system improved. This enables measurements with low tracer concentrations that do not influence the nano-particle generation process or the flame chemistry. An optimized scan range for excitation spectra was applied to measure flame temperatures between 600 and 1500 K in a 175×50 mm² field with an accuracy of ±2%. It was found that the TiO₂ nano-particle generation process does not influence the flame temperature under typical operating conditions. Pressure effects on the temperature distribution were investigated. The data is required for the simulation of nano-particle formation based on kinetic modeling. PACS 07.20.Dt; 42.62.Fi; 61.46.Df     

Cherenkov counter for measuring the intensity of bunches extracted from the IHEP accelerator

The Cherenkov counter for measuring the numbers of protons in bunches extracted from the IHEP accelerator using a slow extraction system is described. The measurement range is from 1 to 10⁶ particle/bunch. The maximum bunch frequency is 6 · 10⁶ s^–1. Cherenkov light is measured by an XP 2020 photomultiplier. The results of measurements of the XP 2020 signal amplitude on the applied voltage, obtained using semiconductor light sources are presented. The data of counter calibration on the proton beam are discussed.