Optical Energy Range Research Articles

Some peculiarities of triplet excitations dynamics in organic macromolecules and crystals

Spectral properties of polymer macromolecules in the optical energy range and relation of these properties to the chemical structure and energy levels system of polymers were examined. The nature of optical centers of the macromolecules with π-electron systems localized on separate groups (so-called chromophores) was analyzed. It was stressed that such vitally important biopolymers as DNA and RNA belong to this type of polymers. It was shown that in synthetic and biological macromolecules with pendant aromatic groups, the triplet excitons meet and annihilate with the very high probability due to large lifetime and one-dimensional motion. The presented results prove that efficiency of triplet-triplet annihilation processes (at the used excitation power) is higher than efficiencies of other electronic processes. Consideration of this fact in the kinetic equation for triplet excitons in macromolecule leads to inverse square root dependence of phosphorescence intensity on the macromolecule length. At the same time, for three-dimensional molecular crystals of stilbene and para-terphenyl, the intensity of the delayed fluorescence is less dependent on the size of the granules compared to the dependence of the delayed fluorescence intensity on the length for one-dimensional macromolecules.

Low resistivity Ru1-xTixO2 thin films deposited by hybrid high-power impulse magnetron sputtering and direct current magnetron sputtering technique

The present paper reports on an experimental investigation of the structural, electrical and optical properties of Ru rich Ru1-xTixO2 thin films. Rutile single-phase Ru1-xTixO2 thin films have been deposited by reactive hybrid High-power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) at a substrate temperature of 250 °C. The HiPIMS source was applied to the Ru target while the DCMS source was connected to the Ti target in order to vary the Ti content in the films. The films are well crystallized and compact with randomly orientated nanocrystallites. The optical properties have been investigated by ellipsometric measurements in the optical energy range from 1.3 eV to 3.3 eV, while the electrical resistivity has been measured in the Van der Paw configuration at room temperature. The electrical resistivity increases gradually from 70 μΩcm for pure RuO2 to about 243 μΩcm for Ru1-xTixO2 films with x = 0.13. The optical properties are correlated with the Ti doping. The refractive index n changes from a strong dispersion relationship to a moderate one with increasing Ti content.

Narrow band photocurrent response from partially phase separated a-SiNx:H thin films

We report static and dynamic photocurrent response from sub-stoichiometric a-SiNx:H thin films. The photocurrent spectral (PCS) response is peaked in the technologically important optical energy range of 2.2 to 4.5 eV. The transient photocurrent response with prolonged exposure is attributed to reduction in number of charge carriers due to trapping of photo-generated carriers at defect sites. The narrow PCS response is attributed to dominant photo-generation of carriers in the bandtails of stoichiometric Si3N4 phase and subsequent transport through the excess Si network.

Optical observations of PSR J0205+6449 – the next optical pulsar?

PSR J0205+6449 is a young ({\approx} 5400 years), Crab-like pulsar detected in radio and at X and {\gamma}-ray energies and has the third largest spin-down flux among known rotation powered pulsars. It also powers a bright synchrotron nebula detected in the optical and X-rays. At a distance of {\approx} 3.2 kpc and with an extinction comparable to the Crab, PSR J0205+6449 is an obvious target for optical observations. We observed PSR J0205+6449 with several optical facilities, including 8m class ground-based telescopes, such as the Gemini and the Gran Telescopio Canarias. We detected a point source, at a significance of 5.5{\sigma}, of magnitude i {\approx} 25.5, at the centre of the optical synchrotron nebula, coincident with the very accurate Chandra and radio positions of the pulsar. Thus, we discovered a candidate optical counterpart to PSR J0205+6449. The pulsar candidate counterpart is also detected in the g ({\approx}27.4) band and weakly in the r ({\approx}26.2) band. Its optical spectrum is fit by a power law with photon index {\Gamma}0 = 1.9{\pm}0.5, proving that the optical emission if of non-thermal origin, is as expected for a young pulsar. The optical photon index is similar to the X-ray one ({\Gamma}X = 1.77{\pm}0.03), although the optical fluxes are below the extrapolation of the X-ray power spectrum. This would indicate the presence of a double spectral break between the X-ray and optical energy range, at variance with what is observed for the Crab and Vela pulsars, but similar to the Large Magellanic Cloud pulsar PSR B0540-69.

CATALOG AND STATISTICAL STUDY OF X-RAY SELECTED BL LACERTAE OBJECTS

This paper presents a catalog of 312 X-ray selected BL Lacerate objects (XBLs), optically identified through the end of 2011. It contains the names from different surveys, equatorial coordinates, redshifts, multifrequency flux values, and luminosities for each source. In addition, the different characteristics of XBLs are statistically investigated (redshift, radio/optical/X-ray luminosities, central black hole (BH) mass, synchrotron peak frequency, broadband spectral indices, optical flux variability). Their values are collected through an extensive bibliographic and database search or calculated by us. The redshifts range from 0.031 to 0.702 with a maximum of the distribution at z = 0.223. The 1.4 GHz luminosities of XBLs log νL ν ~ 39-42 erg s–1 while optical V and X-ray 0.1-2.4 keV bands show log νL ν ~ 43-46 erg s–1. The XBL hosts are elliptical galaxies with effective radii r eff = 3.2625.40 kpc and ellipticities, = 0.040.52. Their R-band absolute magnitudes MR range from –21.11 mag to –24.86 mag with a mean value of –22.83 mag. The V – R indices of the hosts span from 0.61 to 1.52 and reveal a fourth-degree polynomial relationship with z that enables us to evaluate the redshifts of five sources whose V – R indices were determined from the observations but whose irredshifts values are either not found or not confirmed. The XBL nuclei show a wider range of 7.31 mag for MR with the highest luminosity corresponding to MR = –27.24 mag. The masses of central BHs are found in the interval log M BH = 7.39-9.30 solar masses (with distribution maximum at log M BH/M ☉ = 8.30). The synchrotron peak frequencies are spread over the range log νpeak = 14.56–19.18 Hz with a peak of the distribution at log νpeak = 16.60 Hz. The broadband radio-to-optical (α ro ), optical-to-X-ray (α ox ), and radio-to-X-ray (α rx ) spectral indices are distributed in the intervals (0.17,0.59), (0.56,1.48), and (0.41,0.75), respectively. In the optical energy range, the overall flux variability increases, on average, towards shorter wavelengths: Δm = 1.22, 1.50, and 1.82 mag through the R, V, B bands of Johnson-Cousins system, respectively. XBLs seem be optically less variable at the intranight timescales compared to the radio-selected BL Lacs (RBLs).

Electrical and optical properties of Ta-Si-N thin films deposited by reactive magnetron sputtering

The electrical and optical properties of TaxSiyNz thin films deposited by reactive magnetron sputtering from individual Ta and Si targets were studied in order to investigate the effects of nitrogen and silicon contents on both properties and their correlation to the film microstructure. Three sets of fcc-TaxSiyNz thin films were prepared: sub-stoichiometric TaxSiyN0.44, nearly stoichiometric TaxSiyN0.5, and over-stoichiometric TaxSiyN0.56. The optical properties were investigated by near-normal-incidence reflectivity and ellipsometric measurements in the optical energy range from 0.375 eV to 6.8 eV, while the d.c. electrical resistivity was measured in the van der Pauw configuration from 20 K to 300 K. The optical and electrical measurements were interpreted using the standard Drude-Lorentz model and the so-called grain boundary scattering model, respectively. The electronic properties were closely correlated with the compositional and structural modifications of the TaxSiyNz films due to variations in the stoichiometry of the fcc-TaNz system and the addition of Si atoms. According to the nitrogen and silicon contents, fcc-TaxSiyNz films can exhibit room temperature resistivity values ranging from 102 μΩ cm to about 6 × 104 μΩ cm. The interpretation of the experimental temperature-dependent resistivity data within the Grain Boundary Scattering model, combined with the results from optical investigations, showed that the mean electron transmission probability G and the free carriers concentration, N, are the main parameters that control the transport properties of these films. The results indicated that the correlation between electrical and optical measurements with the chemical composition and the nanostructure of the TaxSiyNz thin films provides a pertinent and consistent description of the evolution of the Ta-Si-N system from a solid solution to a nanocomposite material due to the addition of Si atoms.

Condensate of excited states in magnesium

The results of theoretical study of the condensate of excited states in magnesium are reported. Excitations are described in the framework of the Hartree-Fock method taking into account energy level widths. It is shown that conditions for the emergence of condensed excited states are created in the optical range of atomic excitation energies. In the Mg2 system, such conditions are created for any (indefinitely small) excitation fields in the optical energy range. The weaker the external field, the longer the lifetime and the shallower the potential well for the condensate of excitations. Most stable excitations in Mg2 were detected at atomic spacings on the order of 9 Bohr radii.

Anisotropic optical properties of single crystalline PTCDA studied by spectroscopic ellipsometry

We report anisotropic spectra of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) in the optical energy range 1.5–3.7 eV, measured at room temperature by spectroscopic ellipsometry. The results were obtained on single crystals of a-PTCDA grown by temperature gradient sublimation. Spectra were measured at highly symmetric positions of the plane of incidence relative to the sample crystallographic axes and are presented as pseudo-values of refractive index hni and extinction coefficient hki, which reflect a very large anisotropy of these optical functions. The spectroscopic properties of the excited states in the molecular plane (1 0 2) are analyzed; in particular, we identify clear Davydov splittings proving the formation of coherent excitons in the crystal. Out-of-plane, we observe a relatively narrow absorption peak

Optical functions and electronic structure ofCuInSe2,CuGaSe2,CuInS2,andCuGaS2

We report on the complex dielectric tensor components of four chalcopyrite semiconductors in the optical energy range (1.4-5.2 eV, from 0.9 eV for CuInSe2) determined at room temperature by spectroscopic ellipsometry. Our results were obtained on single crystals of CuInSe2, CuGaSe2, CuInS2, and CuGaS2. Values of refractive indices n, extinction coefficients k and normal-incidence reflectivity R in the two different polarizations are given and compared with earlier data where available. We analyze in detail the structures of the dielectric function observed in the studied energy region. Critical-point parameters of electronic transitions are obtained from fitting of numerically calculated second-derivative spectra. Experimental energies and polarizations are discussed on the basis of published band structure calculations.

Lightning Generation in a Jovian Thundercloud: Results from an Axisymmetric Numerical Cloud Model

An axisymmetric cloud model with detailed microphysics was used to calculate the electrical development of a jovian water cloud. The charge separation mechanism was based on the noninductive interaction between ice crystals and graupel particles in the presence of supercooled liquid droplets. The results show that for plausible concentrations of cloud condensation and freezing nuclei in the atmosphere, the electric field in a jovian thundercloud builds rapidly and exceeds its breakdown value. Low concentrations of cloud condensation nuclei produced shallow clouds and did not separate enough charge to produce critical fields. We simulated the lightning discharge by assuming that a flash occurred wherever the electric field, which resulted from the obtained space charge configuration, exceeded the local breakdown value. A lightning flash was assumed to neutralize a 20-Km channel within the cloud. The calculated flash rate suggests that the 192-sec exposure time of Voyager 1 camera, may have captured several superimposed lightning flashes. The energy calculated for such a simulated lightning discharge was of the order of 10 12-10 13 J, which translates to 10 9-10 10 J in the optical energy range, in agreement with Voyager's observations of Jupiter's lightning.

Continuous secondary light emission from silver films: on the origin of the inelastic background in SERS

When cryocondensed silver films at 40 K are excited by laser photons in the optical energy range, a broad distribution of secondary photons with an energy shift from 250 cm −1 to beyond 3500 cm −1 is emitted. Upon annealing to 250 K we observe a narrowing of the emission band accompanied by an order of magnitude increase of the peak emission intensity. The emission is quenched by oxygen exposure. The data are explained by a second order light scattering process involving surface state intraband excitations. Tentatively, the excitation band is assigned to the intrinsic surface state at (111) facets.