Microwave Photonic Signal Down‐Conversion Using a Novel Two‐Frequency Bragg Grating Based Brillouin Fiber Laser

A simple technique using a novel twofrequency Bragg grating based Brillouin fiber laser to downconvert high frequency microwave photonic signals is presented. The mechanism of the Brillouin fiber laser and the principle of this technique for microwave photonic signal downconversion are analyzed. The 12GHz microwave photonic signals are experimentally downconverted to 1.13GHz IF signal with the technique.     

Influence of IR Radiation on the Electron Mobility in Submicron Layers of GaAs

The influence of optical radiation near the impurity absorption band on the electron mobility in submicron doped gallium arsenide layers formed on semiinsulating substrates is investigated. To determine the lowfield mobility of carriers, a method is used which is based on measurements of the mutual conductance and series resistances of a fieldeffect transistor at low sourcetodrain voltage. It has been established that the electron mobility increases under IR illumination as a consequence of decrease in electron scattering, and this is related to the photoneutralization of deeplying chrome acceptors.     

Two‐Wave CO2 Laser with Loss Modulation in Both Channels

The nonlinear dynamics of a twowave CO₂ laser with continuous pumping by an electric discharge and loss modulation in both channels is investigated theoretically. In modulation of losses with the same frequencies it is possible, by changing the shift of the phases of modulating signals, to monitor simply enough the amplitude, form, duration, and depth of modulation and also the repetition rate of radiation. Depending on the shift of phases, the maximum response can be concentrated in the lowfrequency region or propagate also to the region of high frequencies. If losses in both channels are modulated with different frequencies, a change in the relationship between these frequencies predominantly leads to a change in the shape, magnitude, and structure of response in the lowfrequency region of the amplitudefrequency characteristic (AFCh). In the highfrequency region of the amplitudefrequency characteristic, beginning from the peaks of the doubling of the vibration period, where inphase modes of radiation are implemented, the response virtually does not change. Similar regularities are observed on change in the shift of phases.     

Calculation of Out‐of‐Plane Vibrations of a Porphin Molecule

Using the DFT/B3LYP method with the base set 631G^**, we carried out calculation of the frequencies of the normal vibrations of porphin and of its five isotopic types. Scaling of force constants for outofplane vibrations has been performed in independent natural coordinates. The symmetry coordinates are introduced and a force field for outof plane vibrations of a porphin molecule in independent coordinates of symmetry is obtained. A new correlation of the frequencies of vibrations in the type of the symmetry B _1u for the isotopic type of the d ₂ porphin molecule is suggested on the basis of discrete analysis of the distribution of a potential energy.     

Calculation of Quantum‐Chemical Characteristics of the Ground and Excited Electronic States of Porphin and Its Tetrapyrrole Isomers

Using the CNDO/S method, we have performed quantumchemical calculations of the ground and excited electronic states of porphin molecules (symmetry D _2h ) and a number of porphin isomers: porphycene (C_2h ), hemiporphycene, corphycene (C_2v ), isoporphycene, and three nonsynthesized structural isomers of the porphin skeleton by its bridge groups —(CH) _meso —. The results of the calculations are compared with the corresponding data for the freebase porphin molecule (H₂P). Near the boundary between the occupied and vacant orbitals the isomers form rows of singleelectron levels with similar energy characteristics. For the MOs of these isomers, the H₂P MOs closest in distribution on the comparable atomic centers are given. The weak (Q) and strong (B) transitions in the visible and near UV regions point to the porphyrin type of spectra of all the isomers. The calculation data on the excited electronic states of N, g, and ntype H₂P near and above the B states are given; the presence of such states in other isomers is shown. The calculation does not point to a difference in the position of the first singlet transitions in the first five isomers. The calculation data on the lower singlettriplet transitions are also reported.     

An ARC Facility for Studying Carbon Plasma and Obtaining Low‐Dimensional Carbon Structures

An experimental DUF2000 facility for spectroscopic investigations of a reducedpressure carbon arc and also for production of lowdimensional carbon structures (fullerenes, nanotubes, etc.) is described.     

Novel Bandpass Filter Configuration Using Coupled Linear Tapered Line Resonators

A novel tapped bandpass filter composed of twocoupled linear taperedline resonators (LTLRs) is proposed. Multistepped resonators are applied to analyzing LTLRs, which are difficult to analyze directly. Through this analysis method, fundamental characteristics of LTLRs and their filter design parameters can be easily derived. This new filter has insertion loss less than 0.6dB at 1.9 GHz, the return loss less than 18dB in the range 1.81.93GHz and 12.3% 3dB bandwidth. Experimental results of fabricated filter are in good agreement with the design results.     

Equations for the Magnetization Modes in a System Having a Quadruple Nucleus with the Spin S = 1

Within the framework of the method of a density matrix, differential equations are obtained that describe the evolution of the modes of magnetization <Î₊>, <Î_{+ z} >, and <Î_{+ z} ²> for a spin system containing a nucleus with a 1/2 spin connected scalarly with the quadruple nucleus of the spin S = 1 in the presence of crosscorrelation between the dipole ISinteractions, anisotropy of the chemical shift of the I and S nuclei, and quadruple interaction of the S nucleus. The equations are used for analysis of the evolution of the intensities of each line in the triplet of the Raman spectrum of the 1/2 spin. Expressions for the times of crossrelaxation and the times of transverse relaxation of each of the lines of the triplet are obtained.     

Analog of the Auger Effect in Radiative Decay of a Trion in a Quantum Well

We have analyzed the energetics of decay of the X ^minus trion (exciton + electron) on the assumption that the exciton and trion are independent excitations of a single twodimensional semiconducting quantum well. For the first time, it has been shown that in filling a well with electrons from a selective donordoped matrix, the binding energy of the trion (of the electron with the exciton) increases linearly with a shift of the Fermi level into the depth of the c band. This agrees with the wellknown experimental data on the lowtemperature radiative decay (photoluminescence) of trions in the heterostructures ZnSe/Zn_0.89Mg_0.11S_0.18Se_0.82 and CdTe/Cd_0.7Mg_0.3Te.     

Manifestation of Extracoordination in the Resonance Raman Spectra of Water‐Soluble Cation Co‐Porphyrins

Resonance Raman spectra (RRS) of Co(II) and Co(III)5,10,15,20tetrakis(4Nmethylpyridinium)porphyrin ((Co^II(TmpyP4), and Co^III(TMPyP4)) in aqueous solutions at different pH as well as in organic solvents (methanol, ethanol, DMSO, DMF) are obtained. The increased sensitivity of the oscillation frequencies ₂, ₄, ₈, and ₆ — the markers of the oxidation state of a metal — to the nature of an axial ligand has been revealed. For Co^III(TmpyP4), the shifts of the indicated frequencies in extracoordination have turned out to be twofold larger than those for Co^II(TmpyP4). The spectral effects observed are related to different electron influence of the extraligands on the system of the porphyrin ring. In the case of Co(III)porphyrin, interaction of the d orbitals of the metal and the e _g ^*orbitals of the macrocycle is more efficient since its ionic radius is smaller than for the Co(II)complex. For Co^III(TmpyP4), a linear correlation between the oscillation frequencies ₂, ₄, ₈, and ₆ and the experimental Gutmann parameters characterizing the electronacceptor properties of solvents is found.     

Spectral‐Luminescence and Generation Properties of 1‐Aza‐2‐Methyl‐6‐Aminopyrene and of Its Protolytic Forms

Spectral manifestations of protolytic forms of 1aza2methyl6aminopyrene in ethanol and aqueous solutions are investigated. The ionization constants of the protolytic forms are determined. The generation properties and photostability of a neutral molecule and a cation in excitation by an excimer XeCl laser are studied.     

Infrared Spectroscopic Study of N,N‐Dimethylthioformamide Complexes of the Hofmann Type

Four new Hofmanntype complexes, M(DMTF)₂Ni(CN)₄, (where DMTF is dimethylthioformamide, M=Mn, Cd, Co, or Ni) were synthesized and their structure was determined by an elemental analysis and infrared spectroscopy. The IR spectra of DMTF and its nickel tetracyanine complexes with Mn(II), Cd(II), Co(II), and Ni(II) have been investigated within the range 4000–400 cm^–1. The frequency shifts in the metal complexes agree with the assignment of the CS and CN frequencies. The complexes consist of infinite planar polymer layers of |MNi(CN)₄|. Ndimethylthioformamide is coordinated to this layer from above and below; it is a monodentate ligand and is Sbonded through the metal atom in these complexes.     

Calculation of the Tautomeric Properties of 3‐Formyl‐Tetrinic Acid by the ab initio and DFT Methods

We have carried out a nonempirical quantumchemical calculation with full optimization of the geometry of all theoretically possible tautomeric forms of 3formyltetrinic acid (FTRA) according to the Møller–Plesset secondorder perturbation theory with the use of a 6–31G(d) double zeta basis set. The correlation corrections to the total energy of molecules for optimized geometric configurations were calculated in the 631G(d,p) basis. All the possible tautomeric forms of FTRA and the harmonic vibrational frequencies were also calculated within the density functional theory (DFT) with the use of the Perdew–Burke–Ernzerhof (PBE) functional in a threeexponent basis. It is shown that FTRA in vapors (in the perfect gas approximation) exists in the form of a mixture of three enol forms, among which two exoforms predominate. The frequencies and forms of normal vibrations for each cisenol tautomer in the region of vibrations of ketogroups and double bonds differ widely, which permits identification of the tautomers present in the mixture. The possible mechanisms of enolenol transformations of 3acyltetrinic acids are discussed.     

Electroluminescence and Spectral Properties of N9‐Isobutyl‐2‐Oxo‐3‐Phenyl‐3N‐Benzo[F]Chromene‐9‐Sulfonamide

Experimental data on the synthesis and spectral properties (UV, IRFourier, xray photoelectronic, and luminescence spectra) of the sulfonamide derivative of benzocoumarin in an isopropanol solution and in a film applied by thermal vacuum deposition (TVD film) are reported. The use of TVD films of the investigated substance as electroluminophors is shown to be promising.     

Formation Dynamics of Absorbing Layers in a Two‐Stage Atomizer

An experimental spatialresolution facility for recording the formation dynamics of absorbing layers in a twostage atomizer is described. An optical scheme with a convergent raying beam in the atomizer zone and a hollow cathode as a radiation source is considered. The dynamics of the absorptivity signal at evaporation of Rb, NaCl, and a standard sample CASS2 has been investigated under different operating conditions of the atomizer. It is shown that the proposed evaporation–condensation–atomization regime considerably lowers the spatial gradients of absorptivity and the level of nonselective absorption in recording the atomic absorption signal.     

Influence of Close‐Range Dipole‐Dipole Interactions on the Real Part of the Susceptibility of a Dense Resonance Medium

Based on a solution of the stationary modified Bloch equations, an investigation is made of the influence of the effect of internal optical bistability (IOB) on the behavior of the refractive index of a dense resonance medium as a function of the constant b of closerange dipoledipole interactions, frequency detuning, and the intensity of optical radiation. The conditions of existence of the IOB effect of the system dense resonance medium + optical radiation are found and the dynamics of the loop width of the hysteresis dependence of the population difference of the resonance levels of the medium on the characteristics of the system is traced. The domains of the parameters are determined in which the effects of selffocusing and selfdefocusing of the radiation propagating in a dense resonance medium can take place.     

Anti‐Stokes Luminescence of Cadmium Telluride Nanocrystals

For the first time, the antiStokes luminescence in colloidal solutions of CdTe nanocrystals on excitation below the absorption edge has been discovered. The maximum spectral shift to the shortwave region relative to the excitation energy E _con ^max = 319 meV is obtained for meansized nanocrystals (2.5 nm). The conversion efficiency of the absorbed radiant energy is 1.3·10^–2%. The rise in the antiStokes photoluminescence intensity with increasing temperature and the linear dependence on the exciting radiation intensity have been established. It is shown that the effect observed cannot be caused by twophoton excitation or by Auger recombination. It is assumed that the basic mechanism of the luminescence observed is the radiative recombination through the energy levels of the states attributable to the disturbance of the crystal structure in the nanocrystals.     

Kinetics of the Decay of Prolonged Luminescence of Disordered Chrysene under the Conditions of Nonequilibrium Transfer of Energy

We present the results obtained in investigation of the decay of the prolonged luminescence of disordered chrysene in a microsecond range. At the temperature of liquid nitrogen, a highly nonexponential decay of both phosphorescence and annihilation of delayed fluorescence is observed. The observed character of decay is due to relaxation of the energy of electronic excitation in a system of energydisordered centers, when the value of kT is much smaller than the width of the excitedstate energy distribution. At the same time, in the system investigated there is a classical relationship between phosphorescence and delayed fluorescence, i.e., the rate coefficient for the reaction of triplettriplet annihilation is a constant.     

Procedure for Automated Measurement and Calculation of the Electrophysical Parameters of Solar Cells

We described the procedures for automated measurement and calculation of the electrophysical parameters of solar cells on the basis of the IBM PC, a solar radiation simulator, V721A digital voltmeters, and a programcontrolled potentiometer which ensure the programmed assignment of the load resistance in the range 0.002–15,000 and measurement of the light voltampere characteristics of the solar cells, a shortcircuit current, and the opencircuit voltage and also calculated the basic parameters of the solar cells, such as the efficiency, the fullfactor of the voltampere characteristics, optimum and maximum power, optimum load resistance, series and shunt resistance, and the matching factor for the ideal and experimental voltampere characteristic of the solar cells. The error in the measurement and calculation of the solar cell parameters does not exceed 0.2%.     

Updated Analysis of Gallium Chelate and Vanadium Chelate Solutions with 4‐(2‐Pyridylazo)Resorcinol and Xylenol Orange

The characteristic factors of the gallium and vanadium chelates with the ligands 4(2pyridylazo)resorcinol (PAR) and xylenol orange (XO) have been determined with the aid of the principle of correction, which makes it possible to eliminate the influence of the surplus ligand in the solution of its chelate with methane (which makes calculation easier) and thereby provides a more acceptable method in comparison with others. The real molar coefficients of extinction of the chelates Ga and V with PAR and XO have been determined and a detailed calculation of the stoichiometric ratios of chelates has been made. The results have shown that the chelates formed have the following structure: Ga(PAR), Ga(XO), V(PAR)₂, and V(XO).