Dependence Of Signal Intensity Research Articles

Controlling the nonadiabatic dynamics of the charge-transfer process with chirped pulses: Insights from a double-pump time-resolved fluorescence spectroscopy scheme.

The manipulation of the ultrafast quantum dynamics of a molecular system can be achieved through the application of tailored light fields. This has been done in many ways in the past. In our present investigation, we show that it is possible to exert specific control over the nonadiabatic dynamics of a generic model system describing ultrafast charge-transfer within a condensed dissipative environment by using frequency-chirped pulses. By adjusting the external photoexcitation conditions, such as the chirp parameter, we show that the final population of the excitonic and charge-transfer states can be significantly altered, thereby influencing the elementary steps controlling the transfer process. In addition, we introduce an excitation scheme based on double-pump time-resolved fluorescence spectroscopy using chirped-pulse excitations. Here, our findings reveal that chirped excitations enhance the vibrational system dynamics as evidenced by the simulated spectra, where a substantial signal intensity dependence on the chirp is observed. Our simulations show that chirped pulses are a promising tool for steering the dynamics of the charge-transfer process toward a desired target outcome.

Low temperature Overhauser effect in silicon doped with As75 in strong magnetic fields

Peculiarities of the Overhauser effect for arsenic atoms in silicon in a strong magnetic field at low temperatures are considered. Dynamic equations describing the change in the electron paramagnetic resonance (EPR) signal at times exceeding the spin relaxation time have been obtained and solved. Under these conditions, the EPR signal intensity dependence on the pumping time is governed by the rate of the nuclear polarization. It is shown that the degree of nuclear polarization can reach significant value even for relatively weak pumping, and the times of establishment of nonequilibrium nuclear polarization differ significantly from the cross-relaxation time.

Identification and dosimetry of irradiated pistachio (Pistacia vera L.) using EPR

In the current study, the EPR signal of both gamma-irradiated shell and kernel of the pistachio is recorded and investigated. The spectrum properties, microwave power dependency of signal intensities, short- and long-term temporal dependencies, and other significant factors are studied. This investigation was done on how varying radiation doses (0–10 kGy) affected the reactions of pistachio shells and kernels. The time dependence of the radiation-induced signal intensity of pistachio showed that the maximum intensity reached about 98.75% and 67% of its original value for shells and kernels, respectively, after the first six hours. These results indicate that EPR is an effective tool for gamma-irradiated pistachio identification and dosimetry, whether employing pistachio shells or kernels.

Elucidating molecular mechanisms of two-dimensional chemical reactions

Elucidating molecular mechanisms of two-dimensional chemical reactions

Increase in terahertz-wave generation by difference frequency mixing by the overlap of exciton states in different GaAs/AlAs quantum wells and spectroscopic measurements.

Intense terahertz-wave emission in the higher frequency region can result in various applications such as terahertz spectroscopy and ultrafast data communication. In this study, an increase in terahertz waves by the overlap of exciton states in different quantum wells and spectroscopic demonstration are reported. The excitation energy dependence of signal intensity shows the effect of the overlap. The signals measured under the condition of square dependence of intensity on the excitation power indicate interference with the periods corresponding to the laser energy difference. Furthermore, the absorption coefficient of the transparent sheet is obtained at specific frequency. These results indicate that the generation of intense terahertz waves at various frequencies using excitons is possible and that difference frequency mixing is a useful terahertz-wave source.

Peculiarities of prismatic input of narrow-band radiation into Ag-ion diffusion waveguide

The peculiarities of prism coupling elements input and output of narrow-band radiation into ion diffusion waveguide are researched. Gradient waveguide with a thickness of 1.67 μm was formed by ion exchange in K8 glass. The output signal intensity dependence on the input and output angles of incidence radiation was measured by developed automatic hardware-software system based on synchronous detection method to improve the signal-to-noise ratio. It was shown the maximum of output signal is reached at equal input and output angles.

Annihilation Dynamics of Molecular Excitons Measured at a Single Perturbative Excitation Energy.

Exciton-exciton annihilation (EEA) is a ubiquitous phenomenon, which may limit the efficiency of photovoltaic devices. Conventional methods of determining EEA time scales rely on measuring the intensity dependence of third-order signals. In this work, we directly extract the annihilation rate of molecular excitons in a covalently joined molecular trimer without the need to perform and analyze intensity dependent data by employing fifth-order coherent optical spectroscopy signals emitted into ±2k⃗1 ∓ 2k⃗2 + k⃗3 phase matching directions. Measured two-dimensional line shapes and their time traces are analyzed in the framework of the many-body version of the Frenkel exciton model, extended to incorporate annihilation dynamics. Combining double-sided Feynman diagrams with explicit simulations of the fifth-order response, we identify a single peak as a direct reporter of EEA. We retrieve an annihilation time of 30 fs for the investigated squaraine trimer.

Refractive index modulation of YAG crystal through electronic energy depositions of argon ions

This work has demonstrated the feasibility to modulate the refractive index of YAG crystal at variable depths via electronic energy depositions of argon ions. Surface and buried cladding waveguide layers of various geometries were successfully created, which are capable of effective light confinement and guidance at infrared waveband of 1064 nm. Refractive index profiles of irradiated layers were reconstructed in a reasonable manner according to the variations of electronic stopping powers. Information about the structural damage level of ion irradiated crystal were given by measured micro-Raman spectra and signal intensity dependence on penetration depth. Ridge waveguides with superior guiding performances were also manufactured on the platform of refractive index modulated crystals. Based on the precise index modulation shown in this work, extended applications of active ion doped YAG waveguides with better performances, such as high-efficiency waveguide laser oscillation and high-gain integrated optical signal amplification, could be expected.

Scanning polarization lidar LOSA-M3: opportunity for research of crystalline particle orientation in the ice clouds

Abstract. The article describes a scanning polarization lidar, LOSA-M3, developed at the V. E. Zuev Institute of Atmospheric Optics, the Siberian Branch of the Russian Academy of Sciences (IAO SB RAS), as part of the common use center “Atmosphere”. The first results of studying the crystalline particle orientation by means of this lidar are presented herein. The main features of the LOSA-M3 lidar are the following: (1) an automatic scanning device, which allows changing the sensing direction in the upper hemisphere at the speed up to 1.5∘ s−1 with the accuracy of the angle measurement setting of at least 1 arcmin, (2) separation of the polarization components of the received radiation that is carried out directly behind the receiving telescope without installing the elements distorting polarization, such as dichroic mirrors and beam splitters, and (3) continuous alternation of the initial polarization state (linear–circular) from pulse to pulse that makes it possible to evaluate some elements of the scattering matrix. For testing lidar performance several series of measurements of the ice cloud structure in the zenith scan mode were carried out in Tomsk in April–June 2018. The results show that the degree of horizontal orientation of particles can vary significantly in different parts of the cloud. The dependence of signal intensity on the tilt angle reflects the distribution of particle deflection relative to the horizontal plane and is well described by the exponential dependence. The values of the cross-polarized component in most cases show a weak decline of intensity with the angle. However, these variations are smaller than the measurement errors. We can conclude that they are practically independent of the tilt angle. In most cases the scattering intensity at the wavelength of 532 nm has a wider distribution than at 1064 nm.

Vibrational Imaging and Quantification of Two-Dimensional Hexagonal Boron Nitride with Stimulated Raman Scattering.

Hexagonal boron nitride (h-BN) is an important member of two-dimensional (2D) materials with a large direct bandgap, and has attracted growing interest in ultraviolet optoelectronics and nanoelectronics. Compared with graphene and graphite, h-BN has weak Raman effect because of the far off-resonance excitation; hence, it is difficult to exploit Raman spectroscopy to characterize important properties of 2D h-BN, such as thickness, doping, and strain effects. Here, we applied stimulated Raman scattering (SRS) to enhance the sensitivity of the E2g Raman mode of h-BN. We showed that SRS microscopy achieves rapid high resolution imaging of h-BN with a pixel dwell time 4 orders of magnitude smaller than conventional spontaneous Raman microscopy. Moreover, the near-perfect linear dependence of signal intensity on h-BN thickness and isotropic polarization dependence allow convenient determination of the flake thickness with SRS imaging. Our results indicated that SRS microscopy provides a promising tool for high-speed quantification of h-BN and holds the potential for vibrational imaging of 2D materials.

Rapid and direct mass spectrometric analysis of antibiotics in seawater samples.

A method based on droplet spray ionization (DSI) mass spectrometry was described for rapid, direct analysis of seawater samples. By spontaneous desalting (SD) of droplet seawater on a cover slip corner, the target analytes could be separated from the salts. The separated targets are then dissolved in a spray solvent for mass spectrometric analysis. The desorption/ionization of salts is impeded due to their microsolubility or even insolubility in the spray solvent, thus greatly reducing the suppression of ionization of the analyte. It has been demonstrated that the desalting process is spontaneous and highly effective, which simplifies the operation. The dependence of signal intensity on the operation parameters was investigated as well. With this method, a wide range of antibiotics including sulfonamides, macrolides, amphenicols, quinolones, rifamycins, and mixtures in seawater have been successfully detected in either positive or negative ion modes. Limits of detection (S/N ≥ 3) were determined to be 0.52 and 0.20 pg for trimethoprim and clarithromycin, respectively. Moreover, satisfactory accuracy and precision were obtained according to the analysis of real seawater samples. Our results show that the combination of DSI and spontaneous desalting is a simple, sensitive, and rapid method for direct detection of analytes in seawater.

A high‐performance multifunctional substrate of ultrathin‐layer chromatography (UTLC) and surface‐enhanced Raman scattering (SERS) for rapid biochemical mixture screening

AbstractWe present a multifunctional substrate of ultrathin‐layer chromatography (UTLC) and surface‐enhanced Raman scattering (SERS), which enables analytes separation and label‐free detection simultaneously. This integrated substrate is composed of silicon nanowires array (SiNWA), decorated with silver nano‐dendrites (AgNDs). This SiNWA is fabricated by a facile and low‐cost metal‐assisted chemical etching process, and the AgNDs are then decorated onto SiNWA by chemical reduction process. These AgNDs provide abundant hot spots by inducing strong localized electric field, which is confirmed by finite‐difference time‐domain simulation calculations. With the optimized multifunctional substrate, the screening of melamine is successfully validated. The high linear dependence of signal intensity and melamine concentrations from 15 to 1,500 ppm with small deviation was carried out by our developed UTLC–SERS substrate, providing a great potential for quantitative detection. Besides, the SERS signals further show a low relative standard deviation of 8.7%, benefited from the calibration by a peak located at 520 cm−1 of silicon. In short, such a low‐cost, high‐stable multifunctional substrate of UTLC and SERS can be readily employed for practical applications of rapid biochemical mixture screening.

Optimization of detection range of hydrazides of carboxylic acids and 2-acylhydrazinсarbothioamids by HPLC-ECI-MC

Elaboration of control steps of hydrazids and сarbothioamids, raw materials in the synthesis of 1,2,4-triazol-3-yl-thioacetate acids, potential drug substances on research and production stage is an important task. The study of adsorption, distribution, metabolism and excretion of these substances has great importance. The HPLC-MS is the most universal and selective method used in these cases.
 The aim of our study was to determine the optimal conditions for mass spectrometric detection of ionization in electrospray in HPLC-MS іzonіcotinohydrazide, furan-2-carbohydrazide, 2-morpholinoacetohydrazide, 2-methoxybenzohydrazide, 2-isonicotinoyl-N-(2-methoxyphenyl)hydrazine-1-carbothioamide, 2-(furan-2-carbonyl)-N-phenylhydrazine-1-carbothioamide, 2-(2-morpholinoacetyl)-N-phenylhydrazine-1-carbothioamide, N-methyl-2-(2-morpholinoacetyl)hydrazine-1-carbothioamide, 2-(2-methoxybenzoyl)hydrazine-1-carbothioamide, precursor substances in the synthesis of salts of 1,2,4-triazol-3-yl-thioacetate acids for 8 synthetic schemes using full factorial design on 3 factors and polynomial regression equations.
 Work was carried out using flow injection analysis (the technique of direct sample introduction into the ion source) on a liquid chromatograph Agilent 1260 Infinity HPLC System with a single quadrupole mass spectrometer Agilent 6120.
 The optimal conditions of mass spectrometric detection series hydrazides and сarbothioamides for HPLC-ESI-MS on the basis of the calculated maxima polynomial regression functions were obtained. The equation of polynomial regression for the corresponding hydrazides and carbatioamides were suggested. The equations show the dependence of the mass detector signal intensity on three important factors: dryng gas temperature, the fragmentor voltage, the nebulizer pressure. The optimal conditions of mass spectrometric detection choice to maximize the signal detector and thus increase the sensitivity and selectivity of the determinations. It may allow partially separate the signal of these substances from the impurities signal because these conditions have specificity.

ESR Study of Irradiated Polysaccharides ESR investigation of gamma irradiated pectin

Polysaccharides irradiation is usually used for their decontamination of fungi, pathogenic bacteria, toxigenic molds, parasitic organisms. ESR studies are performed just to evidence their irradiation. Therefore the accent is put on radical stability in time and ESR signal intensity dependence on irradiation dose. Less attention is given to radical nature and their dependence on plant nature. In this report a study of gamma irradiated pectin is given. Dose dependence of double integrated ESR signal is analyzed in terms of a recombination reaction during the radiation period. Radical stability dependence on water content is put in evidence.

Resolution enhancement of pump–probe microscope with an inverse-annular filter

Optical pump–probe microscopy can provide images by detecting changes in probe light intensity induced by stimulated emission, photoinduced absorbance change, or photothermal-induced refractive index change in either transmission or reflection mode. Photothermal microscopy, which is one type of optical pump–probe microscopy, has intrinsically super resolution capability due to the bilinear dependence of signal intensity of pump and probe. We introduce new techniques for further resolution enhancement and fast imaging in photothermal microscope. First, we introduce a new pupil filter, an inverse-annular pupil filter in a pump–probe photothermal microscope, which provides resolution enhancement in three dimensions. The resolutions are proved to be improved in lateral and axial directions by imaging experiment using 20-nm gold nanoparticles. The improvement in X (perpendicular to the common pump and probe polarization direction), Y (parallel to the polarization direction), and Z (axial direction) are by 15 ± 6, 8 ± 8, and 21 ± 2% from the resolution without a pupil filter. The resolution enhancement is even better than the calculation using vector field, which predicts the corresponding enhancement of 11, 8, and 6%. The discussion is made to explain the unexpected results. We also demonstrate the photothermal imaging of thick biological samples (cells from rabbit intestine and kidney) stained with hematoxylin and eosin dye with the inverse-annular filter. Second, a fast, high-sensitivity photothermal microscope is developed by implementing a spatially segmented balanced detection scheme into a laser scanning microscope using a Galvano mirror. We confirm a 4.9 times improvement in signal-to-noise ratio in the spatially segmented balanced detection compared with that of conventional detection. The system demonstrates simultaneous bi-modal photothermal and confocal fluorescence imaging of transgenic mouse brain tissue with a pixel dwell time of 20 µs. The fluorescence image visualizes neurons expressing yellow fluorescence proteins, while the photothermal signal detected endogenous chromophores in the mouse brain, allowing 3D visualization of the distribution of various features such as blood cells and fine structures most probably due to lipids. This imaging modality was constructed using compact and cost-effective laser diodes, and will thus be widely useful in the life and medical sciences. Third, we have made further resolution improvement of high-sensitivity laser scanning photothermal microscopy by applying non-linear detection. By this, the new method has super resolution with 61 and 42% enhancement from the diffraction limit values of the probe and pump wavelengths, respectively, by a second-order non-linear scheme and a high-frame rate in a laser scanning microscope. The maximum resolution is determined to be 160 nm in the second-order non-linear detection mode and 270 nm in the linear detection mode by the PT signal of GNPs. The pixel rate and frame rate for 300 × 300 pixel image are 50 µs and 4.5 s, respectively. The pixel and frame rate are shorter than the rates, those are 1 ms and 100 s, using the piezo-driven stage system.

Hyperfine Structure in the OD ESR Spectra of Recombining Charge Pairs in Doped Polyethylene Matrices

The hyperfine structure has been resolved in the optically detected electron spin resonance (OD ESR) spectra of radical ion pairs generated by ionizing radiation at a low dopant concentration in a solid polyethylene matrix at room temperature. The different organic molecules that can capture electrons and holes were used as the dopants. The spin-lattice relaxation times T1 for radical ions of dopants were estimated to be tens of microseconds. The temperature dependence of OD ESR signal intensity indicates the diffusion-assisted mechanism of recombination of radical ion pairs in polyethylene.

Influence of behaviors of magnetic particles in ferrofluids under alternating magnetic fields on harmonic responses

We describe the relationship between the excitation frequency dependence of harmonic signal intensity under alternating magnetic fields and the hydrodynamic size of magnetic particles in ferrofluids. The hydrodynamic size estimated from magnetic susceptibility increases with the increase in ion and particle concentrations in the ferrofluids. The excitation frequency dependence of the fifth-harmonic signal intensity exhibits a minimum point at a certain frequency. The frequency of the minimum point shifts to the lower-frequency range, and after reaching the minimum, it increases with the increase in ion and particle concentrations, reflecting the increase in hydrodynamic size owing to the aggregation of magnetic particles. These behaviors may be useful for applications in ion sensing by a magnetic technique.

Preparation of CuGaO<sub>2</sub> Thin Film by a Sol-Gel Method Using Two Kinds of Metal Source Combination

We prepare CuGaO2 thin films on SiO2 substrates by using the sol-gel spin-coating method with two combinations of Cu and a Ga source, Cu and Ga nitrate, or acetylacetonate. X-ray diffraction analysis reveals that the thin films prepared using nitrate sol that are annealed at a temperature of 850°C - 950°C show both c-axis-orientated peaks, (006) and a non-c-axis-oriented peak (012) with similar intensity; little dependence of signal intensity on annealing temperature is also shown. The films are opaque in appearance at these annealing temperatures. Scanning electron microscope observation reveals that the opaque appearance is due to the texture or cracks on the surface of the films. In contrast, the films prepared using acetylacetonate show a (006) peak with higher signal intensity than the (012) peaks. The films show more transparent appearance than that of the films by nitrate. The highest conductivity of the film is 5.7 × 10-4Ω-1·cm-1, obtained in the films by nitrate annealed at 850°C.

Preparation of Copper-Doped Nickel Oxide Thin Films by Sol-Gel Method Using Nickel and Copper Acetate

We have prepared nondoped and Cu-doped NiO thin films by sol-gel method on SiO2 substrate using nickel acetate and copper acetate as precursors. Thin films of NiO were formed by thermal annealing of gel films at 500 - 900°C for 10 h in air. X-ray diffraction (XRD) peaks of NiO have been observed at higher annealing temperature than 500°C, and intensity of the peaks increased with annealing temperature until 800°C. On the other hand, the dependency of XRD signal intensity on annealing temperature becomes less significant by Cu-doping. Nondoped NiO films show high transparency at lower annealing temperatures than 800°C. The result means that the film with high crystalline volume ratio is not consistent with the films with high transparency. Cu-doping decreases the transmittance of the films with low crystalline volume ratio. It is considered that the doped Cu atoms exist in amorphous fraction make the transmittance lower. Conductivity of the films is increased with Cu-doping only in the films annealed at 500 - 700°C. The highest conductivity obtained in the Cu-doped film is around 10-6 W-1cm-1 at 600°C. On the other hand, the Cu-doped films show similar conductivity to nondoped films at high annealing temperature, 800 or 900°C.

Differentiated correction on the signal intensity dependence of GasBench II-IRMS from blank effect and instrument nonlinear effect

Continuous-Flow Isotope Ratio Mass Spectrometry (CF-IRMS) coupled with a GasBench II was designed to rapidly analyze δ13C in carbonate or CO2 in air. The dependence of measured δ13C (δ13Cm) on signal intensity (peak area or peak height) was the main error source resulting from blank effect of samples and/or instrument itself effect. To determine the reasons and origins of signal intensity dependence, eight signal intensity gradients for two carbonate (δ13C values were −49.64 and 1.61‰, respectively) and a gas mixture of 0.3% CO2 in He (δ13C=−19.32‰) standards were made respectively. The results showed that there was obvious signal intensity dependence, in particular when sample amount (peak area) was smaller. Given that the dependence was caused by blank effect and/or instrument nonlinear effect, without considering the blank effect, the signal intensity dependence could not be eliminated directly by the instrument nonlinear correction (empirical equation) methods However, it could be eliminated by blank correction (indirect subtraction method). In practice, blank effect should be corrected first, and then the instrument nonlinear effect.