Electro-optic Method Research Articles

Synthesis and Properties of Highly Tilted Antiferroelectric Liquid Crystalline (R) Enantiomers.

This work reports the synthesis method and various properties of four rod-like antiferroelectric (R) laterally substituted enantiomers, with or without fluorine atoms used as substituents in the benzene ring. The influence of fluorine substitution on the mesophase temperature range was determined. The synthesized compounds are three-ring rod-like smectics with a chiral center based on (R)-(-)-2-octanol. Their chemical and optical purity was checked using high-performance liquid chromatography (HPLC). Two newly synthesized enantiomers and three previously reported (R) enantiomers were used to formulate two antiferroelectric mixtures. The mesomorphic behavior was characterized by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction (XRD). The helical pitch and tilt angle measurements were done using the selective light reflection phenomenon and the electro-optical method, respectively. All the enantiomers exhibit a wide temperature range of the antiferroelectric phase, with a high tilt angle. Furthermore, the enantiomer with lateral fluorine substitution in the ortho position has a very long helical pitch (more than 2.0 µm), relatively low enthalpy of melting point, and a tilt angle close to 45 degrees. The designed (R) enantiomers can be useful for formulating eutectic mixtures for further use in various devices, including photonics and optoelectronics.

Characterizing third-order intermodulation distortion of photodetectors based on de-coupling and de-embedding modulation distortion of modulators

A novel, to the best of our knowledge, electro-optical modulation method is proposed for measuring third-order intermodulation distortion of photodetectors (PDs) based on de-coupling and de-embedding modulation distortion of modulators. The method utilizes dual parallel intensity modulation to generate electro-optical stimulus signals with fast and fine sweeping capability, and it eliminates the nonlinear impact of modulators by using low-frequency bias swing, allowing a direct extraction of the third-order output intercept point (OIP3) of PD from the combined nonlinear response contributed by both the modulators and the PD. The OIP3 of PD is frequency-swept measured with our method and compared to those with the conventional method to check for consistency. The proposed method enables a modulator-distortion-free, fast, and fine sweeping measurement of PDs using a simple system.

A study of the frequency characteristics of downhole penetration by Audio electric perspective method

There are many factors affecting the safe production of coal mines, and mine water damage is the most prominent one. In the field operation, we should find out the old air water, water-rich aquifer and geological structure of the mining face and its surroundings, so as to eliminate the hazards of mine water damage to the people's lives and properties. At present, there are many mature and effective methods for underground anomaly detection, and this paper adopts the audio electro-optical perspective method for early warning detection of mine water-bearing areas. First of all, through the reasoning research on the basic theory of electromagnetic field, the equivalent principle of low-frequency alternating current (AC) and direct current (DC) is deduced, which provides the theoretical basis for the research of audio electro-optical perspective; then, through the COMSOL simulation experiments, the penetration frequency characteristics of the downhole are investigated, and the optimal penetration frequency is found in different depths by comparing the strength and stability of the signals. The results of the study have promoted the significance for the improvement and development of the audio electro-penetration method, and have greater reference value for the prevention and control of water damage in coal mines.

On the invasiveness of the electro-optical research method in strong inhomogeneous electric and light fields

On the invasiveness of the electro-optical research method in strong inhomogeneous electric and light fields

POSSIBILITIES OF USING OPTICAL RADIATION DIFFRACTION MANAGEMENT METHODS ON REFLECTIVE COATINGS OF ARMAMENT AND MILITARY EQUIPMENT FOR ITS PROTECTION AGAINST AMMUNITION WITH SEMI-ACTIVE LASER GUIDANCE SYSTEMS

The article substantiates the need to improve the existent methods of combat defense and combat equipment (DAM) against bombs (guided combat munitions from UAVs, stray combat munitions, etc.)with semi-active laser targeting systems (LSA) on the basis of controlled reflective coatings. Methods of management the diffraction of optical radiation on reflecting coatings are based on applications in coating materials. At the same time, the reflecting properties can be purposefully changed by applying acousto-optical, electro-optical and thermos-optical effects. The acousto-optic method of diffraction control involves the spatial modulation of the beating coefficient in the medium, which is carried out by ultrasonic (acoustic) waves. During the distribution of ultrasound in the reflective coverage (areas of compression and discharge of the material of the waves distribution) appears in the reflective coverage. A purposeful change of descriptions of the acoustic wave leads to the possibility of forming the reflecting phase grating with a given parameter on which it will diffract a radiation. The electro-optical method of management the diffraction of laser radiation is based on the phenomenon of induced anisotropy of media under the influence of a field (electro-optical effect). However, the creation of reflective diffractive elements (coatings)using the electro-optical effect is limited by a number of disadvantages of this method. The thermo-optical method of management light diffraction consists in changing the optical constants of reflective coatings under the influence of temperature. On the basis of the multilayer interference systems (MLIS) with tapes, peak and phase diffraction gratings can be implemented. The use of MLIS coatings with ribbons in the display allows you to implement the functions of selecting and unlocking coatings in the infrared range. The last two methods are of the greatest practical interest since, unlike, the electron-beam method they allow heating a fairly large surface area of the coating. The implementation of diffraction control of optical radiation on the reflective coatings of DAM samples will allow to remove the ammunition control system with semi-active LSA from the working state as a result of the aiming point fluctuation.

Transmission-based charge modulation microscopy on conjugated polymer blend field-effect transistors.

Charge modulation microscopy (CMM) is an electro-optical method that is capable of mapping the spatial distribution of induced charges in an organic field-effect transistor (OFET). Here, we report a new (and simple) implementation of CMM in transmission geometry with camera-based imaging. A significant improvement in data acquisition speed (by at least an order of magnitude) has been achieved while preserving the spatial and spectral resolution. To demonstrate the capability of the system, we measured the spatial distribution of the induced charges in an OFET with a polymer blend of indacenodithiophene-co-benzothiadiazole and poly-vinylcarbazole that shows micrometer-scale phase separation. We were able to resolve spatial variations in the accumulated charge density on a length scale of 500nm. We demonstrated through a careful spectral analysis that the measured signal is a genuine charge accumulation signal that is not dominated by optical artifacts.

Synchronous electro-optical method for studying mixed ionic–electronic conductors with hopping transport

Mixed ionic–electronic conductor materials are exploited in energy storage and conversion applications, and, more recently, in emerging ionic thin film devices with distinctive electronic and optical functionalities, that impels studying their properties and, in particular, electrical transport mechanisms. Electrical and optical characterization methods, for instance, relaxation experiments under a small step variation in the mobile ion activity, are routinely used to study transport properties of mixed ionic–electronic conductors. In this work, we develop a theoretical basis for a synchronous electro-optical characterization method that enables fast measurement of the ionic and electronic (small polaron) mobilities, absorption cross section, and defect concentration in mixed ionic–electronic conductors with hopping transport.

Optimization and control of cold atom interference phase shift based on laser double-sideband suppression

Using the electro-optical modulation method to generate Raman beams for cold atom interference is one of the better methods for constructing a more compact and robust laser system. But this way will generate some residual sidebands resulting in the additional interference phase shift, which can affect the measurement accuracy of cold atom interferometer. In order to weaken the effect of laser modulation sidebands on the phase shift of cold atom interference, a double-sideband suppressed-carrier modulation laser system for cold atom interference is constructed. Based on the designed laser system, the principle of double-sideband generation and suppression is analyzed in detail, and some residual sidebands are adjusted and controlled. Moreover, some important optical parameters that affect the phase shift of cold atomic interference, such as the initial distance between the Raman retro-reflection mirror and the atomic cloud, the interrogation time between two adjacent Raman pulses, the laser modulation depth and the initial velocity of the atomic cloud, are discussed and optimized. By optimizing these relevant parameters, the influence of residual modulation sidebands on the phase shift of cold atomic interference is weakened drastically. The research results indicate, making use of the method of double-sideband suppression, the phase shift of cold atomic interference can be optimized to 0.7 mrad when the initial distance between the Raman retro-reflection mirror and the atomic cloud is 105 mm, and the interrogation time between two adjacent Raman pulses is 82 ms. More importantly, this work can provide a method for weakening the influence of Raman sideband effect on the phase shift of cold atom interferometer, and the corresponding laser system can be applied to other inertial sensors such as atomic gravimeter or atomic gravity gradiometer.

Studies of de Vries SmA* type phase in chiral thiobenzoates

ABSTRACT The nature of the SmA*–SmC* phase transition was studied in three chiral liquid crystal compounds, in two belonging to the same homologous series, (S)-1-methylheptyl-4-(4′-alkoxybiphenylthiocarboxy)-benzoates, (S)-MHPSBOn, where n = 7 and 8 is the number of carbon atoms in the alkyl chain and (S)-4-[(4-{1-methylheptylcarboxyl} phenyl) carbonylthio] phenyl-4′-decyloxy-1-benzenecarboxylate (10OPOSMH). Compounds (S)-MHPSBO7 and (S)-MHPSBO8 show different behavior in the SmA*–SmC* phase transition, in MHPSBO7 the SmA* phase is the de Vries phase, while in MHPSBO8 it is the classic SmA* phase. The aim of the study is to demonstrate the presence of the de Vries type SmA * phase in three chiral thiobenzoates. The electro-optical method and SAXS were used to analyze the SmA*–SmC* transition.

Optical Methods for Studying Pre-Breakdown Phenomena in Liquid Dielectrics

Three main groups of non-invasive experimental methods (shadow, spectral, and electro-optical) for studying pre-breakdown processes in liquid dielectrics are reviewed. Each of these methods has its own capabilities and allows a limited set of information about the process under study to be obtained. High-speed shooting makes it possible to record emerging objects and trace the dynamics of the processes occurring in the discharge gap. Shadow methods make it possible, by recording changes in the probing radiation in a real-time mode, to obtain information about the course of processes in a liquid, during which a change in the refractive index occurs. However, neither of these two methods allows the obtained data to be linked to the electrical characteristics of the object under study. Spectral research methods make it possible to consider the effect of high voltage on the physicochemical processes occurring in the discharge gap. To do this, it is advisable to combine them with high-speed shooting methods, but the low intensity of the studied radiation and the high speed of the processes add much difficulty to the use of such methods. If the processes occurring at the molecular and atomic levels are set aside, the electro-optical research method remains the only one that links the electrical parameters of the object under study with the obtained optical picture of the processes. Moreover, with a growth in the field strength, additional features appear in the electro-optical pattern due to the the Kerr effect nonlinearity, as a result of which the characteristic processes that precede the breakdown can be noticed. It is shown, using the electro-optical Kerr effect as an example, how the use of modern computer-aided experimental data processing methods helps obtain additional information that was previously inaccessible.

Bubble growth and detachment process in surfactant solutions: a study of 90% pure sodium dodecyl sulfate

We have investigated the effect of the surfactant Sodium Dodecyl Sulfate on the bubble growth and detachment processes in a bubble column system. A modified pendant drop model was employed to determine the dynamic surface tension. The dynamic surface tension approached the static surface tension value within a few seconds. A photographic technique and a laser-based electro-optical method were used to study the bubble size variation and the generation frequency, respectively. Parameters like bubble generation frequency, size, growth rate, and contact angle were found to be a strong function of surfactant concentration. Our results show that the addition of surfactant significantly reduces the bubble lifetime at the orifice. Such a decrease in the bubble lifetime has a direct impact on the bubble growth rate and departure size. Furthermore, bubble parameters vary with surfactant concentration only up to the critical micellar concentration.

Dual chirped-pulse electro-optical frequency comb method for simultaneous molecular spectroscopy and dynamics studies: formic acid in the terahertz region.

An electro-optic dual-comb system based on chirped-pulse waveforms is used to simultaneously acquire temporally magnified rapid passage signals and normal spectral line shapes from the back-transformation to the time domain. Multi-heterodyne terahertz (THz) wave generation and detection is performed with the difference frequency mixing of two free-running lasers. The method is used to obtain THz spectra of formic acid in the 10 cm-1 to 20 cm-1 (300 GHz-600 GHz) region over a range of pressures. The method is widely applicable across other spectral regions for investigations of the transient dynamics and spectroscopy of molecular systems.

Nonequilibrium phase transitions of a nematic liquid crystal under ac field-driven electroconvection.

We report on phase transitions between isotropic and nematic liquid crystal phases in nonequilibrium systems (NESs). ac field-driven electroconvection (EC) provides an NES, which can be well controlled by the voltage V and frequency f; it arises electrohydrodynamically at a threshold voltage V_{c}. In continuous cooling and heating processes with various rates R, the critical temperature T_{c} was determined at a critical time t_{c} for phase transitions. Moreover, the morphological and dynamical features in the phase transitions were examined using an electro-optical image processing method. In comparison with an equilibrium system (V=0), two typical turbulent ECs (i.e., NESs), which are called dynamic scattering mode 1 (DSM1 for V>V_{c}) and DSM2 (for V≫V_{c}), were examined to understand the nonequilibrium phase transitions. In particular, our results show that in high voltage-induced turbulence (i.e., DSM2), T_{c} can be determined effectively without considering R; this provides a possibility for a material technology application in nonequilibrium-based circumstances.

Active and Smart Terahertz Electro-Optic Modulator Based on VO2 Structure.

Modulating terahertz (THz) waves actively and smartly through an external field is highly desired in the development of THz spectroscopic devices. Here, we demonstrate an active and smart electro-optic THz modulator based on a strongly correlated electron oxide vanadium dioxide (VO2). With milliampere current excitation on the VO2 thin film, the transmission, reflection, absorption, and phase of THz waves can be modulated efficiently. In particular, the antireflection condition can be actively achieved and the modulation depth reaches 99.9%, accompanied by a 180° phase switching. Repeated and current scanning experiments confirm the high stability and multibit modulation of this electro-optic modulation. Most strikingly, by utilizing a feedback loop of "THz-electro-THz" geometry, a smart electro-optic THz control is realized. For instance, the antireflection condition can be stabilized precisely no matter what the initial condition is and how the external environment changes. The proposed electro-optic THz modulation method, taking advantage of strongly correlated electron material, opens up avenues for the realization of THz smart devices.

Simulation of subnanosecond radio pulse electro-optical repeater

Objectives . The study aimed to construct and analyze a computational model of an electro-optical repeater of radio pulses, capable of reconstructing a pulsed radio image with subnanosecond resolution in a single reception under conditions of additive noise. Methods . Numerical methods of network analysis were used, which are the basis of specialized computer-aided design systems, numerical methods of statistical radio engineering. Results . A radiophotonic radio pulse repeater scheme was constructed, which is implemented based on the principle of fractional multiplexing with delayed feedback. Software simulation of infrared repeaters in the Simulink environment (Trial Version Soft) was developed, which allows for analyzing and investigating the efficiency of the optical reconstruction method of radio pulses using a fractional multiplexing with delayed feedback. It is shown that repeaters schemes, implemented on the principles of fractional multiplexing with delayed feedback, are able to effectively solve the scientific and practical problems of multiple probing of objects with ultrashort pulses (USP) for obtaining a radio image of a target with reliable reproducibility. In the course of numerical simulations, it was found that the two- and four-cascade schemes of delay lines with feedback do not provide reliable reproducibility in the case of reconstruction of an ultrashort pulse with a complex time profile. At the same time, the scheme with a cascade of 8 delay lines showed good results, providing a correlation reproducibility of more than 0.9. In this case, the scheme of an electro-optical repeater with a cascade of 16 delay lines did not make a significant contribution to increasing the accuracy of the USP reconstruction if compared to the scheme with a cascade of 8 lines; therefore, the latter can be determined as an optimal solution. An electro-optical method was proposed for solving the radio engineering problem of stroboscopic registration and reconstruction of subnanosecond radio pulses, which represent the signature of the radio image of dynamic objects for active radio imaging systems. Conclusions . It was found that an electro-optical repeater with 8 delay lines is able to recover a complex pulse reflected from a target in 30 iterations with a correlation coefficient greater than 0.9 between the reference and reconstructed pulses at a signal-to-noise ratio of at least 9 dB.

High precision even-power phase modulation method for a self-mixing displacement sensor under the weak feedback regime.

A novel method called even-power phase modulation is proposed in a self-mixing displacement sensor to improve measuring accuracy, to the best of our knowledge, which is realized by combining the even-power fast algorithm with the sinusoidal phase-modulation method. By performing the even-power fast algorithm in the self-mixing interference system, the spectrum of harmonic components is broadened. In this case, the extracted first and second harmonic components in the frequency domain contain rich information, and the displacement of the target can be accurately reconstructed. The principle and signal processing approach are introduced in detail, and the simulation results show that the reconstruction error can be effectively reduced compared with the electro-optic modulator phase modulation method. A series of experiments at different vibration amplitudes is conducted to confirm the feasibility and effectiveness of the method. An amplitude of 120 nm is proved to be measurable, and the absolute error is 10 nm, which shows great potential in the field of non-contact nanometer vibration measurement sensors.

Simultaneous frequency response measurement of electro-absorption modulation transceivers based on a self-referenced pilot operation.

An electro-optic method based on a self-referenced pilot operation is proposed for simultaneously characterizing electro-absorption modulation optoelectronic transceivers with a shared setup. Through inserting and extracting the self-referenced pilot, the frequency responses of electro-absorption modulated lasers (EMLs) and photodetectors (PDs) are independently obtained in a single measurement, and any extra optical-to-electrical or electrical-to-optical calibration is avoided. Specifically, the relative frequency response of the EML at fm is determined through the extracted difference-frequency pilot at fp (close to DC), realizing the low-frequency analysis for an EML. The relative frequency response of PD at 2fm+fp is obtained from the amplitude ratio of the extracted sum- and difference-frequency pilots at 2fm+fp and fp under the microwave driving signal at fm, verifying the doubled measuring frequency range. In the proof-of-concept demonstration, the frequency response of an electro-absorption modulation transceiver is measured up to 40 GHz. Thereinto, the frequency response of the EML is obtained by detecting the fixed low-frequency pilot of 10 kHz, and the frequency response of the PD is extracted with frequency-swept modulation to 20 GHz. The experiment results are compared with those obtained with the electro-optic frequency sweeping method to check for accuracy.

Resonant Electro-Optic Imaging for Microscopy at Nanosecond Resolution.

We demonstrate an electro-optic wide-field method to enable fluorescence lifetime microscopy (FLIM) with high throughput and single-molecule sensitivity. Resonantly driven Pockels cells are used to efficiently gate images at 39 MHz, allowing fluorescence lifetime to be captured on standard camera sensors. Lifetime imaging of single molecules is enabled in wide field with exposure times of less than 100 ms. This capability allows combination of wide-field FLIM with single-molecule super-resolution localization microscopy. Fast single-molecule dynamics such as FRET and molecular binding events are captured from wide-field images without prior spatial knowledge. A lifetime sensitivity of 1.9 times the photon shot-noise limit is achieved, and high throughput is shown by acquiring wide-field FLIM images with millisecond exposure and >108 photons per frame. Resonant electro-optic FLIM allows lifetime contrast in any wide-field microscopy method.

An Electro-Optical Method for Differential Diagnosis of Pathologies of Blood Supply to the Brain

This work is devoted to the development of a new simplified method for express diagnostics of cerebral blood supply disorders of a vertebrogenic and non-vertebral nature based on electrocardiogram and photoplethysmogram data. The research was conducted using the example of vertebral artery syndrome in osteochondrosis of the cervical spine and somatoform dysfunction of the autonomic nervous system, respectively. Several experimental studies into the dynamics of heart rate variability and differential indicators of the coordinated work of the heart and blood vessels were carried out according to the data of electrocardiography and photoplethysmography. Three experimental groups included healthy volunteers and volunteers with cerebral blood supply disorders connected with either the loss of plasticity and narrowing of brain blood vessels or their mechanical squeezing. According to the research results, statistically significant (with a significance level of less than 0.05) differences by a number of indicators were revealed between the experimental groups. A conventional discriminant analysis of the indicators of the coordinated work of the heart and blood vessels was carried out for all experimental groups in order to determine criteria for differentiating people with vertebrogenic disorders, non-vertebral disorders and healthy volunteers. It is concluded that three variables can be used for such differentiation, each of which describes the coordinated work of the heart and blood vessels in a specific way.

Influence of gamma radiation on measurement fast pulse voltages by Kerr electro-optic effect

In this paper, the possibility of measuring the electronic pulse from an electronic generator for plasma heating by electro-optical method is considered. The experiments are performed by applying the Kerr effect on an electronic generator model. Kerr effect shows very good characteristics for measuring nanosecond pulse rate. However, the results obtained show that these characteristics are significantly spoiled by gamma radiation in a dynamic state as well as by the absorbed dose of gamma radiation. When the simplicity of measuring with a capacitive probe is added to that, it can be concluded that the Kerr electro-optical effect is not recommended for measurement in fusion experiments.