Instruments and Experimental Techniques最新文献

Straw tubes with resistive cathode and cathode readout were successfully manufactured and tested. The straw tubes were manufactured by ultrasonic welding technique. The resistive cathode electrode was made of diamond like carbon (DLC). The possibility of cathode signal readout from external strip electrodes was successfully demonstrated. The event coordinate along the straw can be accurately determined by applying center of gravity method to the individual strip signals.

We describe a technique for online control of the reliability of the data of magnetic circular dichroism spectroscopy in reflected light, which is based on measuring the polar magneto-optical Kerr effect under normal incidence of light on a sample with a method of phase modulation of a light wave using a photoelastic modulator. The presented technique involves measuring the amplitudes of signals at the “zero” (V₌) and doubled (V_2f) frequency f of the retardation modulation in crossed polarizers in the process of scanning over a spectrum. In these measurements, the constancy of the V_2f/V₌ ratio over the entire spectral range confirms the reliability of the spectroscopy data. The possible instrumental errors that lead to a distortion of the recorded spectrum shape were analyzed. The operability and efficiency of the technique is illustrated by an example of measuring the magnetic circular dichroism spectrum of a MnAs film.

The characteristics of the calibration beam of secondary electrons at the Pakhra accelerator based on the SP-3 magnet at the Lebedev Physical Institute are presented. The energy resolution of a beam with a 2-mm-thick copper converter in the electron energy range E = 5–100 MeV is δ ≈ 10%.

Theoretical and experimental studies of the magnetic field distribution in the space between two cylindrical permanent magnets with through holes in the center have been carried out. In the middle of a space measuring 2 × 2 × 2 mm³ near the symmetry axis, a magnetic field with an inhomogeneity of no more than 3% was found and one in the region of 1 × 1 × 1 mm³ with less than 1% was found. Based on the calculated and experimental results, a setup for determining the Verdet constant (V) using neodymium permanent magnets was developed and manufactured. The magneto-optical constants for samples of optical ceramics from Tb₂O₃ and Tb₃Ga₅O₁₂ at wavelengths of 0.628 and 1.06 µm are determined.

A new architecture of a fiber phase-sensitive optical time-domain reflectometer (φ-OTDR, i.e., a distributed acoustic sensor) suitable for engineering geology application is proposed. The sensor is based on a double-pulse scheme in which a pair of pulses is formed using an unbalanced Michelson interferometer. A symmetrical 3 × 3 coupler built into the Michelson interferometer is used to obtain the phase delay needed for the demodulation of the backscattered light. Using the unbalanced Michelson interferometer in the circuit for dual-pulse probe signal generation, it is possible to reduce the requirements for the degree of coherence of the light source, since the delay line introduced between the dual-pulse parts is compensated in the φ‑OTDR fiber under test. As a result, it is possible to use a laser with a wide spectral line (~1 GHz) and generate short (7-ns-wide) laser pulses by directly modulating the laser-diode injection current. In order to reduce the signal fading in the φ-OTDR and to improve the linearity of its response, responses are averaged over 16 optical frequencies. The efficiency of the proposed distributed acoustic sensor has been demonstrated by detecting a strong impact on a cable that was horizontally buried in the ground as well as by detecting seismic waves using a cable inserted in a well at the sea bottom.

The paper proposes a new method for the frequency shift determination of the spectrum obtained under conditions of low resolution of the analyzer, which allows, due to mathematical processing of the signal describing the spectrum, to determine its frequency shift with a resolution two orders of magnitude greater than the instrumental one. The method is based on representing a signal describing a frequency-shifted spectrum as a continuous function differentiable everywhere, expanding it into a Taylor series, approximating its derivatives by finite differences of a given order, and determining the frequency shift by the least squares method. The mathematical substantiation of the method as well as the results of numerical experiments are given. The prospects for the application of the proposed method are discussed.

A schematic diagram of position-sensitive luminescent spark sensors with a spectral radiation converter is considered. By using the sensor, it is possible to detect an electric spark by one or two spatial coordinates depending on the location of the ends of optical fibers. Numerical simulation and optimization of optical systems of position-sensitive luminescent spark sensors has been carried out. The efficiency and resolution of the optical system have been calculated.

Solving the problem of the stability of the manufacturing process (“drawing”) of microstructured optical fibers (“holey fibers”) is of paramount importance for determining effective technological modes of production. In this study, the modified capillary drawing model proposed by the authors, which takes into account inertial, viscous, and surface tension forces, as well as all types of heat transfer, was used. Based on the linear theory of stability, the regions of stability of the capillary drawing process were determined. During the study, the influence of the drawing ratio and inertia forces (Reynolds number) on the stability of the process under consideration was evaluated. The existence of optimal parameters of the heating element is shown: temperature distribution over the furnace surface and furnace radius at which the stability of the process of drawing quartz tubes increases significantly (several times).

A study of the optimal parameters of a distributed fiber microphone circuit based on a laboratory setup of a phase-sensitive optical reflectometer (φ-OTDR), which reproduces the work of φ-OTDR at one point, has been carried out. Various schemes for constructing a microphone based on φ-OTDR and various sampling rates of the analog-to-digital converter are investigated. The optimal configuration of the φ-OTDR circuit is substantiated, which made it possible to ensure high quality of human speech recognition during voice recording by the proposed method with a sampling frequency of 40 kHz. In a standard phrase based on Harvard sentences containing 80 words, 71 words were recognized, i.e., 88.75% of their total number.

The influence of temperature fluctuations of the reference section of an optical fiber as part of the instrumental part on the absolute measurement error of a distributed fiber-optical temperature sensor was performed. The design of the reference section with active temperature control with high stability as part of the instrumental part of the sensor is proposed and experimentally investigated. The efficiency of using active temperature control to improve the repeatability of measurements and reduce the measurement error has been experimentally demonstrated.