Two-channel Scheme Research Articles

High-energy and high-average-power two-channel Yb:YAG amplifier with passive coherent combining

A two-channel laser amplifier with passive coherent combining based on Yb:YAG active elements with bright diode end pumping was developed. The pulse energy limits of a one-channel scheme are investigated, and the ability to double pulse energy in the two-channel scheme is demonstrated. 10 mJ pulse energy at a repetition rate of 1.5 kHz and 5 mJ at 6 kHz simultaneously with high gain and perfect beam quality at coherent combining efficiency over 97% was achieved.

Toward Quantitative Prediction of Fluorescence Quantum Efficiency by Combining Direct Vibrational Conversion and Surface Crossing: BODIPYs as an Example.

Accurate theoretical description of the electronic structure of boron dipyrromethene (BODIPY) molecules has been a challenge, let alone the prediction of fluorescence quantum efficiency. In this Letter, we show that the electronic structures of BODIPYs can be accurately evaluated via the spin-flip time-dependent density functional theory with the B3LYP functional. With the resulting electronic structures, the experimental spectral line shapes of representative BODIPYs are successfully reproduced by our previously developed thermal vibration correlation function method. Most importantly, a two-channel scheme is proposed to describe the internal conversion of S1 to S0 in BODIPYs: channel I via direct vibrational relaxation within the harmonic region and channel II via a distorted S0/S1 minimum energy crossing point well away from the harmonic region. The fluorescence quantum yields are accurately predicted within this two-channel scheme, which can therefore serve as a generalized method for predicting the photophysical parameters of organic fluorescent compounds.

Compact Dual-Band Antenna Module for Glonass/GPS GNSS Receivers

A compact dual-band navigation antenna module, consisting of a planar patch antenna element and a two-channel low-noise amplifier with input protection elements, is proposed. The two-channel scheme for constructing the low-noise amplifier is implemented with the use of two duplex filters, which are calculated by the method of oriented graphs. The patch antenna element is realized in a topology that allows it to be excited at the fundamental resonant mode TM10 both in the lower (L2) and upper (L1) frequency bands, which ensures the identity of the radiation pattern shapes in both frequency bands. The design of the antenna module, the equivalent circuit, the VSWR against frequency, the gain against frequency, the radiation patterns at the central frequencies of the L1 and L2 ranges of the antenna element, the gain and noise figure of the low-noise amplifier against frequency, and the radiation pattern of the entire module are presented.

Technology of Measuring Air Parameters Aboard the Single-Rotor Helicopter Using a Fixed Multifunctional Receiver

The technology is revealed for measuring air parameters aboard the single-rotor helicopter using the information of the aerodynamic field of a main rotor vortex column perceived by a fixed multifunctional receiver made as a two-channel scheme with an ion-mark and aerometric channels. The algorithms of forming and processing the information, technical characteristics of the system obtained by the results of the study of experimental samples in the wind tunnel are given.

Electrodynamic treatment by electric current pulses as effective method of control of stress-strain states and improvement of life of welded structures

The present work was aimed at the development of the new technological process: a postweld electrodynamic treatment of welded joints by pulses of a high-density current. Basing on the numerical solution of Maxwell’s equations for the case of a pulsed electromagnetic field the calculation model of distribution of field components was designed on the basis of integral equations, which allow determining the electromagnetic forces P and current density j in aluminium alloy AMg6 during the process of capacitive energy storage discharge. The calculation data allow accounting for influence of dynamic stresses and electric plasticity effect on change in a stressed state of a metal during the electrodynamic treatment. Comparison of calculated and experimental results showed a good correlation of the obtained data. Using the model, the parameters of the electrodynamic treatment, providing the reduction of residual stresses in welded joints of alloy AMg6, were determined. Generators of the pulse current and electrode devices, realizing the preset parameters of electrodynamic effects at single- and two-channel schemes were designed and manufactured. Results of experimental investigations, carried out on specimens of base metal and welded joints showed that the electrodynamic treatment has a positive effect on structure of the treated metal and allows decreasing greatly the residual stresses in welded joints, increasing their resistance to fatigue and brittle fracture, as well as eliminating the distortion deformations in thin-walled elements of structures. The developed technologies and equipment gave an opportunity to perform the electrodynamic treatment of welded joints of hull structures of ships of aluminium alloy AMg6 and repair welds of an intermediate casing of the aircraft engine of heat-resistant magnesium alloy ML10, thus promoting the increase in their service reliability and life.

Software and Instrumentational Methods of Enhancing the Resolution in Electrochemical Noise Measurements

Several methods of enhancing the signal-to-noise ratio for instrumentation designed to measure electrochemical noise are practically tested. The experiments are carried out using model RC-circuits and lielectrolyte electrochemical cells. Strong limitations in the tested objects’ impedance values are found due to the input current noise of the instrumentation, especially during the parallel connection of several channels. The advantages of a two-channel scheme for automatically compensating the instrument’s self noise are demonstrated. Different methods of lowering the dispersion of the frequency dependences of the spectral power density of electrochemical noise are compared. It is shown that averaging over segments with an overlap is the most effective method but averaging over frequencies can lead to large distortions when investigating electrochemical systems.

Development of Post-weld Electrodynamic Treatment Using Electric Current Pulses for Control of Stress-Strain States and Improvement of Life of Welded Structures

Abstract The present work was aimed at the development of a new technological process: a post-weld electrodynamic treatment of welded joints by pulses of a high-density current. Generators of the pulse current and electrode devices, realizing the preset parameters of electrodynamic effects at single- and two-channel schemes, were designed and manufactured. The results of experimental investigations, carried out on specimens of base metal and welded joints, showed that the electrodynamic treatment has a positive effect on the structure of the treated metal and allows the residual stresses in welded joints to decrease gently, increasing their resistance to fatigue and brittle fracture as well as eliminating the distortion deformations in thin-walled elements of structures. The developed technologies and equipment gave an opportunity to perform the electrodynamic treatment of welded joints of hull structures of ships of aluminum alloy AMg6 and repair welds of an intermediate casing of the aircraft engine of heat-resistant magnesium alloy ML10, thus promoting an increase in their service reliability and life.

Based on FP LDs with split band technique in two-channel fiber optical CATV transport system

This study proposes a two-channel fiber optic cable television (CATV) transport system based on Fabry–Perot laser diodes (FP-LDs) with a split band technique. To reduce the interference between channels, we apply the split band technique to two channels with different frequencies by using two converters at each moment. In this two-channel transmission scheme, composite second-order (CSO) and composite triple-beat (CTB) distortions induced by the systems are possibly confined in unused channels and result in good transmission performances. Through a 40 km standard single-mode fiber transmission, excellent performances of carrier-to-noise ratio (≥50 dB), CSO (≥70 dB), and CTB (≥72 dB) are obtained using the proposed fiber optic CATV transport systems. The proposed systems employing FP-LDs with a split band technique are also simpler and more cost effective than conventional externally modulated systems.

False spectra formation in the differential two-channel scheme of the laser Doppler flowmeter.

Noise in the differential two-channel scheme of a classic laser Doppler flowmetry (LDF) instrument was studied. Formation of false spectral components in the output signal due to beating of electrical signals in the differential amplifier was found out. The improved block-diagram of the flowmeter was developed allowing to reduce the noise.

Creation of nonperturbative horizontal panel of operating table for mobile hospital in the helicopter

An elastic interaction of angular motion of the helicopter fuselage with the operating table panel is analyzed as the object of research. An urgent surgery for victim immediately after its delivery to the helicopter is made possible through three-axis stabilization of the operating table panel of mobile hospital in the vehicle, in particular, in the form of modular construction in a helicopter. Functional content is based on the use of Petrov two-channel principle for formation of operating table structure that invariant to external disturbances. A mathematical model of mobile hospital is developed and construction accuracy of horizontal panel in a stochastic structure of the angular motion of the helicopter is evaluated. The values of mathematical expectation of the platform drift relative to the stabilization axes are defined. It is recommended to use differential two inertial sensors for each stabilization channel. It is proposed to carry out a further increase in the stabilization accuracy by the introduction of negative feedback on the sum of the sensor signals that are common for two gyroscopes The research results can be used by medical services in conjunction with transport organizations responsible for the maintenance of mobile hospitals. Advantages of two-channel scheme for inertial sensors are in suppressing of the influence of instantaneous values of external disturbances as a stochastic angular motion of the vehicle.

Combined Password Authentication Scheme Resistant to Shoulder Surfing Attacks

In this paper, we propose combined password authentication scheme resistant to shoulder surfing attack. Proposed scheme improves the vulnerable part of text-based password authentication scheme about shoulder surfing. Our scheme combined existing text-based authentication factors with user behavior information as the part of the user authentication. Thus, our scheme consider the user efficiency. Because none of other devices is required as a secondary authentication method that is required in two-channel authentication scheme. In addition, our scheme offer the same level of user confirmation factor, as in two-channel authentication scheme. Furthermore, even if text-based password is exposed by shoulder surfing attack, another authentication factor-user behavior patternis not vulnerable to this attack. User behavior pattern is biometric data that reflects users own behavior. Thus, that is hard to copy as same as the original. Therefore, our scheme is shoulder surfing resistant.

A Stable and Transparent Microscale Force Feedback Teleoperation System

Scaled force feedback teleoperation is a promising approach to assist an operator engaged in a microscale task. Several systems were previously described to achieve such purpose, but much room was left for improvement, especially with regard to the specificities of bilateral coupling with very large scaling coefficients. Here, the objective is to render at human-scale haptic information available at the microscale, and to provide scaled teleoperation that simultaneously achieves stability and transparency. An active force sensor and a novel haptic interface were interconnected to form a complete teleoperation chain through a direct, two-channel scheme. Stability was ensured by enforcing passivity in the slave and in the master subsystems. Several experiments were carried out to demonstrate the capabilities of the system. The first experiment involved noncontact magnetic interaction. A second set of experiments demonstrated the penetration of a thin-glass probe in a water droplet where the operator interactively felt capillary forces.

Application of a two-channel fibre-optic Mach-Zehnder interferometer for deformation measurement

Abstract A method for the determination of the deformation direction for a fibre-optic deformometer is proposed. The method is based on the two-channel scheme of a fibre-optic Mach-Zehnder interferometer.

Dark Matter Particle Detection System SQUID - Magnetic Calorimeter

Physical principles underlying the concept of the Dark Matter (DM) are considered. Problems of Dark Matter particle detection are briefly reviewed. An original two-channel scheme for direct detection of cosmic DM particles is proposed. It is based on a super-low-temperature calorimeter and includes a nuclear spin system whose magnetic response is measured by a quantum interferometer (SQUID). Low threshold and the capability for efficiently suppressing the recoil-electron background are the most important advantages of the proposed scheme. They make it possible to detect DM particles with extremely low recoil energies and carry out direct DM search with high sensitivity.

High Bit Rate Fiber-Optic Transmission Using a Four-Chaotic-Semiconductor-Laser Scheme

Successful high-speed fiber-optic transmission using a four-chaotic-semiconductor-laser system is numerically demonstrated. The system performance is benefited from the properties of bandwidth enhancement and the implementation of a two-channel scheme. The bit-error rate of the recovered message is evaluated for different fiber lengths and message bit rates, respectively. In particular, acceptable communication performance can be achieved for a bit rate up to 8 Gb/s when the fiber length is approximately 60 km. Such a system could lead to high-speed chaos-based encryption/decryption even if the fiber transmission module is considered.

Two-channel scheme for dark matter particle detection based on a low-temperature magnetic calorimeter

Problems of dark matter (DM) particle detection are briefly reviewed. An original two-channel scheme for direct detection of cosmic DM particles is proposed. This scheme is based on a superlow-temperature calorimeter which includes a nuclear spin system whose magnetic response is measured by a quantum interferometer (SQUID). Low threshold and the capability for efficiently suppressing the recoil-electron background are the most important advantages of the proposed scheme. They make it possible to detect DM particles in the range of extremely low recoil energies and carry out direct DM search with high sensitivity.

Peculiarites of second harmonic generation of radiation from a pulsed ytterbium-doped fibre laser in KTiOPO4 crystals

Second harmonic generation of radiation from a high-power fibre Yb3+ laser is studied upon sf—f phase matching near the X axis of the KTP crystal (KTiOPO4). The temperature dependence of the phase-matching wavelength as well as its spectral, angular and temperature tuning characteristics of the second harmonic generator are experimentally measured. It is found that the increase in the average output power of the second harmonic in a single crystal is limited, first of all, by the thermal self-focusing of radiation caused by the absorption of radiation from the second harmonic, whose threshold decreases with increasing the crystal temperature. When the two-channel scheme is used, the maximum stable ∼4-W output power of the second harmonic is obtained in two tandem KTP crystals.

Determination of liquid-crystal polar anchoring energy by electrical measurements

We propose a simple method for the determination of liquid-crystal (LC) polar anchoring energy by electrical measurements. The basic idea of this method is a two-channel scheme for capacitance measurements. The first channel uses one cell with a planar LC cell, while the second a LC cell with vertical alignment. One of the LC cells can have a high pretilt angle. The proposed method allows investigating anchoring properties of both planar and vertical aligned LC materials. Simultaneous measurements of the two cells compensate all volume effects in LC bulk and provide a good opportunity to study directly the LC-surface interaction. The method can be applied for LC cells, which do not have uniform azimuthal orientation. We used this method to investigate the polar anchoring properties of photoaligning material before and after illumination and for LC structures with a high pretilt angle.

5.3: Determination of the Polar Anchoring Energy by Electrical Measurement

We propose a simple method for determination of polar anchoring coefficient by electrical measurements. The basic idea of this method is a two-channel scheme for capacitance measurements. The first channel uses one cell with planar alignment LC, the second channel uses the cell with vertical alignment (VA). Such method gives a possibility to investigate anchoring properties of planar and vertical alignment materials. Measurements of two cells at one time give possibility to compensate all volume effects in LC cell and investigate only surface effects. The method can be used for the cells, which do not have uniform planar or VA orientation. We applied this method to investigate the polar anchoring properties of photoaligning material before and after illumination.

Time-resolved phase spectroscopy from femtosecond free-induction decay

We report a novel two-channel experimental scheme to record femtosecond amplitude and phase dynamics for dephasing studies. The measurement of free-induction decay in one channel and pulse autocorrelation for the central wavelength of the exciting pulses at the other channel as the reference allows the recording of time-resolved amplitude and phase dynamics of the free-induction decay throughout the dephasing process. The technique is applied to the study of coherent dynamics of the photocarriers in semiconductor GaAs. The observed phase dynamics is well simulated with optical Bloch vector components analysis for the homogeneously broadened two-level model and the experimental and theoretical study is extended for the three-level system. The two-pulse-induced phase spectroscopy should be generally applicable to different kinds of materials by recording the population difference for the two-level system with pulse-induced fluorescence.