Long-wave Edge Research Articles

Reliable wavelength detection method of sapphire fiber Bragg gratings using added multimode fiber

Sapphire fiber Bragg gratings (SFBGs) are promising high-temperature sensors, which can be applied to measure temperature and strain in extreme environments. However, the multimode operation of SFBGs is susceptible to disturbance, leading to unreliable wavelength detection. Here, we propose by using added multimode fibers (AMMF) and tracing the longwave edge of reflection envelope to enhance the stability of wavelength detection for SFBG. The near-field profiles of transmission modes are investigated in sapphire fiber with different lengths of AMMF. It is found that the mode-field distribution of sapphire fiber can be improved by using AMMF with a length of 1000 m, which results in a reduction of relative standard deviation (RSD) from 57 % to 10 %. Then, the signal-to-noise ratio (SNR) in the reflection spectrum of SFBG is improved to 16 dB by polishing inclined end faces of sapphire fiber using the removal mechanism of hard-brittle materials. Furthermore, we detect the wavelengths of both the longwave edge and peak on the reflection envelope, which reveals lower fluctuations (i.e., SD = 0.02 nm) of the longwave edge, since lower-order modes are more stable during transmission. The effect of external disturbances (i.e., torsion and vibration) on demodulation of SFBG is also evaluated, with a maximum fluctuation of 0.06 nm (SD = 0.01 nm). A temperature experiment is carried out with the assembly and polynomial fitting curves with high fitness are obtained. Thus, our proposed methods enhance the reliability of wavelength detection in the reflection spectrum of SFBG, which is beneficial to improving the sensing performance of SFBG-based sensors.

Photophysical Processes in Indole Molecules in Ethanol at 77 K During Excitation at the Long-Wave Edge of the Absorption Spectrum

Photophysical Processes in Indole Molecules in Ethanol at 77 K During Excitation at the Long-Wave Edge of the Absorption Spectrum

Simulation of CrIS Radiances Accounting for Realistic Properties of the Instrument Responsivity That Result in Spectral Ringing Features

This paper provides a procedure for the simulation of radiances from the U. S. National Oceanic and Atmospheric Administration (NOAA) Cross-track Infrared Sounder (CrIS) Fourier Transform Spectrometer to include spectral ringing effects caused by the finite-band, non-flat instrument spectral response to incident radiation. A simulation using a line-by-line radiative transfer model is performed to illustrate the magnitude of the effect and to indicate which spectral channels are likely to be impacted. Comparisons with CrIS observations are made to show that for most channels this effect is negligibly small compared to errors in the radiative transfer calculations but for the longwave edge of the CrIS longwave band and a few other regions, the brightness temperature ringing is significant. While the ringing artifact described in this paper may appear to be removed when Hamming apodization is applied, as is done for the assimilation of CrIS data into Numerical Weather Prediction (NWP) models, it is still present, and its influence reappears if the spectral correlation induced by apodization is properly handled to preserve the information content that derives from high spectral resolution. Inclusion of the instrument responsivity in calculated spectra to properly mimic the observed spectra as defined here eliminates artifacts from this type of ringing. Users of CrIS radiances should consider whether this effect is important for their application.

Polymethine Dye as Sensors of NH3 and CO

We have investigated the properties of polymethine dyes (PMD) and the purpose of using them as sensors of hazardous gases presence. Research indicates that in case of utilizing PMD as a sensor of hazardous gases we need to use the monochromatic light which wavelength corresponds to the inflection point of the long-wave absorption edge of PMD. Such sensor of hazardous gases can detect changes in the optical density of the sensor layer or the light intensity transmitted through the layer.

The Temperature Dependence of the Thermodynamic Density of States and Urbach Rule

It is invited statistical explanation of the frequency and temperature dependence of the absorption coefficients of semiconductors on the long-wave edge of the fundamental absorption. With the help of mathematical modeling, it shows that the thermal broadening of the energy states of the conduction band and the discrete states in the band gap can cause long-wave decline according to the Urbach rule.

TEMPERATURE DYNAMICS OF POLARIZATION SENSITIVITY SPECTRA OF INTRINSIC OXIDE–p-InSe HETEROJUNCTIONS

Temperature dependence of the photopleochroism coefficient for the intrinsic oxide–pInSe heterojunction was investigated. We observed different temperature dependence of the shift of longwave edge of photocurrent for two polarization orientations: Е||С and Е┴С.

Facile synthesis, growth mechanism, and optical properties of CdSe nanoparticles in self-assembled micellar media and their efficient conjugation with proteins

This article demonstrates the influence of various surfactants of different polarities—anionic, sodium dodecyl sulfate, cationic, hexadecyltrimethylammonium bromide and non-ionic, and polyoxyethylene iso-octyl phenyl ether (TX-100)—on the formation of CdSe nanoparticles in aqueous solutions. The surfactant-stabilizing effect has been monitored using transmission electron microscopy. Spectral properties of CdSe nanoparticles have been investigated; the structure of the long-wave edge of the fundamental absorption band of CdSe nanoparticles has been analyzed. It has been shown that the variation of the synthesizing conditions (stabilizer’s nature and concentration, CdSe concentration, etc.) allows the tailoring of the CdSe nanoparticle size in the range of 8–17 nm. Lifshitz–Slyrzov–Wagner kinetic analysis has also been performed using the size variation according to ripening temperature and time period. The differences in the stabilization ability of tested substances are discussed with respect to their structure and possible mechanism of the surface interaction with the nanoparticles. The flexible surface chemistry of the CdSe-micelles causes them to be water soluble and allows their further conjugation with protein molecules through electrostatic attraction. The interaction between functionalized CdSe nanoparticles with protein molecules have been investigated using fluorescence spectroscopy.

Zinc sulfide nanoparticles: Spectral properties and photocatalytic activity in metals reduction reactions

Formation of zinc sulfide nanocrystals in aqueous solutions of various polymers has been studied. Spectral properties of ZnS nanoparticles have been investigated, the structure of the long-wave edge of the fundamental absorption band of ZnS nanocrystals has been analyzed. It has been shown that the variation of the synthesis conditions (stabilizer nature and concentration, solution viscosity, ZnS concentration, etc.) allows tailoring of the ZnS nanocrystals size in the range of 3–10 nm.

Calculation of the Spectrum of Spontaneous Emission by a Many-Particle Electron-Hole System with Coulomb Interaction of Carriers

Based on numerical solution of the many-particle Schrodinger equation, the spontaneous emission spectrum of two and three interacting electron-hole pairs has been modeled. It is shown that the longwave edge of the emission spectrum decays exponentially and the asymmetry of the form factor of the lines of spontaneous transitions increases on decrease in temperature.

Tunable Photoluminescence Spectra of Doped Semiconductor Superlattices

Taking into account the density state tails appearing due to fluctuations of impurity concentrations, the spontaneous emission spectra of doped semiconductor superlattices are calculated. In the framework of the model developed, the explanation of the experimentally observed longwave edge and the shift of the photoluminescence spectra with increase in the excitation level and temperature is given. The role of the defects formed on α-irradiation is discussed, and the lifetime of current carriers is evaluated depending on the design parameters and excitation conditions of the GaAs doped superlattices.

Photoresponse spectral investigations for anisotropic semiconductor InSe

Photoresponse spectra of anisotropic InSe crystals are investigated depending on the orientation of an illuminated sample surface with respect to light direction. We have detected the differences in the photoresponse spectra in the E∥C and E⊥C configurations. They consist in a different energy location of the long-wave edge of the fundamental absorption, the shift is 0.13 eV, as well as their shape. The room temperature presence of an intensive narrow peak at the edge of the photoresponce spectra was only observed in the E∥C configuration and is connected to excitonic absorption. Its excitonic origination is confirmed by the low-temperature measurements. In the framework of the three-dimensional model of excitons we have determined the binding energy of direct excitons equal to 65±1.8 meV. It is established for the effect of photopleochroism to be observed at the illumination of the (1 1 0) surface by an in-plane polarized light. In the wavelength range 1.03–1.06 μm a measured coefficient of photopleochroism has the value of about 60% and is caused by the anisotropic properties of layered InSe.

Manifestation of vibronic intensity borrowing in fluorescence spectra of metalloporphyrins

In selective laser excitation and at T=4.2 K, fine-structure spectra of the fluorescence of the complexes of Mg, Zn, In, and TiO with octaethylporphyrin are obtained. It is shown that the fine-structure fluorescence spectra of these compounds are formed to a large aegree by ribronic interaction between quasi-degenerate S1 and S2 electron states. An increase in the relative intensities of a number of negatively polarized fluorescence lines in displacement of the excitation line from a longwave edge of the band of an S0→S1 transition in the shortwave direction is revealed.

Photoelectric properties of In/p-(Cu, Ag)Ga(Se, Te)2 surface-barrier structures

Based on single crystals of AgGaSe2, AgGaTe2, CuGaTe2 of the p-type, surface-barrier structures were manufactured by vacuum thermal deposition on illumination of which the photovoltaic effect was observed. It is established that the longwave edge of the photosensitivity of such structures possesses several inflections attributable to photoactive absorption involving paracipation of levels of lattice defects. It is shown that In/p-(Cu, Ag)Ga(Se, Te)2 surface-barrier structures can be used as wide-band transducers and photoanalyzers of linearily polarized radiation.

Structural effects in the electron absorptio and luminescence spectra of decaborane(14) derivatives B10H12L2

The electron absorption and luminescence spectra of some adducts B10H12L2 with L-alkylsubstituted pyridines are compared. In each subgroup with mono- and disubstituted pyridines, the largest hypsochromic shift of the long-wave edge of the charge transfer band (CTB) and the increased fluorescence yield correspond to the maximum basicity of L. Steric strains between the ortho methyl group of L and |B10H12| result in an insignificant bathochromic shift of the CTB and decrease the fluorescence yield. The optimal interactions |B10H12|→L, which are responsible for the absorption and emission properties of the adducts, should correspond to conformations where the planes of the heterocyclic system of L make an angle of 30° and are symmetric relative to the |B10H12| plane.

Photoelectric properties of In2O3-CdSiAs2 structures

Photosensitive rectifying heterostructures were prepared based on single crystals of p-CdSiAs2 doped with group-III impurities by depositing In2O3 layers. It was established that the slope of the long-wave edge of the photosensitivity of the obtained structures decreases as the CdSiAs2 hole concentration increases. Based on polarization investigations of the photocurrent, a conclusion is drawn concerning the possibilities for practical application of diode structures in polarization photoelectronics.

Electron-hole plasma and electron-hole liquid in layered indium selenide

Photoluminescence spectra of layered indium selenide have been stadied in wide temperature range 4.2 + 100 K and a wide interval of optical excitation density (Nex). It is demonstrated that the longwave edge of the K-line undergoes a violet shift with increasing temperature, which confirms the conclusion of /1/ that the K-line (hvmax=1.32 eV) is due to radiative recombination of the e-h pairs in electron-hole liquid (EHL). At pulse excitation (Nex ∼ 1022 phot/sm2.sec) a broad band is observed at the place of excitonic emission lines. The form of this band is described satisfactorily by recombination of the electron-hole plasma. The e-h plasma temperature on the excitation level is estimated. The character of electric field influence upon radiative recombination spectra allows to discuss the mechanism of EHL origin in InSe.

On the nanosecond mobility in proteins. Edge excitation fluorescence red shift of protein-bound 2-(p-toluidinylnaphthalene)-6-sulfonate.

The fluorescence of 2-(p-toluidinylnaphthalene)-6-sulfonate associated with beta-lactoglobulin, beta-casein, and bovine and human serum albumins are shown to depend on excitation wavelength. A long-wave shift of the spectra is observed at the long-wave edge excitation, reaching 10 nm and above. A similar phenomenon is found in glucose glass and in glycerol at +1 degrees C, i.e., in systems with delayed dipolar solvent relaxation, but not in liquid solutions. This phenomenon is proposed to be based on relaxation processes in the excited state. There exists a distribution of chromophore microstates with different interactions with surrounding groups which results in heterogeneous broadening of the electronic spectra and allows photoselection of a part of this distribution, being characterized by a low transition energy. The fast structural relaxation results in an altered distribution and, if this is the case, the effect of edge excitation of fluorescence spectra is not observed. If the structural relaxation during the excited state lifetime is absent, this effect is maximal. This interpretation is in agreement with results on the influence of red edge excitation on the low-temperature fluorescence spectra of dyes and with the data on time-resolved nanosecond fluorescence spectroscopy. The results of this work strongly support the significant dye fluorescence spectral shifts on protein binding, being determined not only by polarity changes in their environment, but also by relaxation properties of protein groups in this environment. These results also indicate that on the nanosecond time scale, the structural relaxation around the excited chromophore in proteins may be incomplete.

Acceptor boron in α-SiC (6H): Investigation by the photocapacitance method

Recombination centres in luminescent crystals n-SiC(6H) doped with nitrogen and compensated with boron during the diffusion process are investigated by photocapacitance method. Boron diffusion results in appearance of a deep centre which is able to capture holes effectively. The ionization energy of this centre ET = (0.4 ± 0.02) eV coincides with the boron ionization energy in p-SiC(6H): B crystals and the spectral dependence of photoionization cross-section qp is similar to the spectral dependence of absorption near the long-wave edge of the absorption band of these crystals. But such centre is not observed in n-SiC(6H): B original samples in spite of the large quantity of boron in them. Based on these facts the conclusion can be made that boron with respect to the capture of the holes may be either in active or in bound states depending on the method of doping. This results in different efficiency of photoluminescence of crystals doped with boron in the growth and diffusion processes. [Russian Text Ignored].

Fluorescence energy transfer studies on the active site of papain.

Measurements have been performed of the excited-state lifetimes and fluorescence yields of papain tryptophan units when acyl derivatives of Phe-glycinal are bound at the active site of the enzyme. The enhancement of tryptophan fluorescence in complexes of papain with the acetyl or benzyloxycarbonyl derivatives is not stereospecific with respect to the configuration of the phenylalanyl residue, and the L and D isomers are equally effective as active-site-directed inhibitors of papain action. Evidence is offered in favor of the conclusion that this enhancement is primarily a consequence of the interaction of the phenylalanyl side chain of the inhibitor with Trp-69 of the enzyme. This residue can exchange fluorescence energy with the other four tryptophans of papain (Trp-7, Trp-26, Trp-177, Trp-181) upon excitation near their absorption maxima, but such "homotransfer" is absent if they are excited at the long-wave edge of their absorption spectra. Crystallographic data indicate that Trp-26 is most favorably positioned for efficient energy exchange with Trp-69, and the fluorescence data have been used to calculate a distance of 11 A between the two residues; this value is in satisfactory agreement with that found by crystallography. When derivatives of Phe-glycinal bearing an amino-terminal mansyl [6-(N-methylanilino)-2-naphthalene sulfonyl] group are bound at the active site of papain, the tryptophan fluorescence is quenched, as compared with that of the complex of papain with acetyl-Phe-glycinal, indicating energy transfer from papain tryptophan (most probably via Trp-26) to the fluorescent probe group. Although the L and D isomers of mansyl-Phe-glycinal are equally effective as inhibitors of papain action, the fluorescence quenching by the two isomers is different.

Photoconductivity and dember effect in Zn 3P 2∗

The photovoltaic properties of Zn 2P 2 monocrystals in photoconductivity (PC) and Dember photovoltaic (D-PV) modes have been investigated in the 0.5–1.2 μm wavelength range. The analysis of long-wave edge and a possible application as a high-sensitivity detector are presented.