Anomalous Absorption Research Articles

Anomalous absorption in glycolaldehyde in a cosmic object

The glycolaldehyde is detected towards the Galactic center source Sgr B2(N) and towards the massive star-forming region G31.41+0.31 through b-type transitions. The levels for b-type transitions can be classified into two groups: (i) with ka+kc = odd (set I) and (ii) with ka+kc = even (set II). For each of the sets I and II, we have calculated energies of 100 rotational levels. These levels are connected through radiative and collisional transitions. The Einstein A-coefficients for the radiative transitions among the levels are calculated. The collisional rate coefficients are calculated with the help of a scaling law. Using the radiative and collisional transitions probabilities, for each of the sets I and II, we have solved a set of statistical equilibrium equations coupled with the equations of radiative transfer. Two transitions 110−101 and 312−303 at 13.477 GHz and 17.981 GHz, respectively, of set I, and one transition 211−202 at 15.176 GHz of set II are found to have anomalous absorption. These transitions may play important role in the identification of glycolaldehyde in a cosmic object.

Enhanced absorption of surface plasma wave by metal nano-particles in the presence of external magnetic field

The absorption of surface plasma wave (SPW) by metal nanoparticles embedded on the metal surface is studied in the presence of an external magnetic field. As a surface wave of frequency propagates through nanoparticles, electrons start oscillating and anomalous absorption of energy takes place at resonance frequency , where is the plasma frequency of electrons inside the nanoparticles. The absorption of the surface plasma wave by the nanoparticles enhances significantly in the presence of a magnetic field at modified resonance frequency (where is the cyclotron frequency). The absorption constant is directly proportional to the cube of a nanoparticle radius and inversely proportional to the square of interparticle separation. Maximum absorption constant is achieved for gold nanoparticles of the radius with interparticle separation and normalized cyclotron frequency . These results are of direct importance in nanoparticle based magneto-plasma solar cells.

Metamaterial Absorbers for Infrared Detection of Molecular Self-Assembled Monolayers.

The emerging field of plasmonic metamaterials has introduced new degree of freedom to manipulate optical field from nano to macroscopic scale, offering an attractive platform for sensing applications. So far, metamaterial sensor concepts, however, have focused on hot-spot engineering to improve the near-field enhancement, rather than fully exploiting tailored material properties. Here, we present a novel spectroscopic technique based on the metamaterial infrared (IR) absorber allowing for a low-background detection scheme as well as significant plasmonic enhancement. Specifically, we experimentally demonstrate the resonant coupling of plasmonic modes of a metamaterial absorber and IR vibrational modes of a molecular self-assembled monolayer. The metamaterial consisting of an array of Au/MgF2/Au structures exhibits an anomalous absorption at ~3000 cm−1, which spectrally overlaps with C-H stretching vibrational modes. Symmetric/asymmetric C-H stretching modes of a 16-Mercaptohexadecanoic acid monolayer are clearly observed as Fano-like anti-resonance peaks within a broad plasmonic absorption of the metamaterial. Spectral analysis using Fano line-shape fitting reveals the underlying resonant interference in plasmon-molecular coupled systems. Our metamaterial approach achieves the attomole sensitivity with a large signal-to-noise ratio in the far-field measurement, thus may open up new avenues for realizing ultrasensitive IR inspection technologies.

Fusion Research in Ioffe Institute

In this paper we present the fusion related activities of the Plasma Physics Division at the Ioffe Institute. The first experiments on lower hybrid current drive (LHCD) in a spherical tokamak performed at the Globus-M tokamak (R = 0.36 m, a = 0.24 m, Bt = 0.4 T, Ip = 200 kA) with a novel poloidally oriented grill resulted in an RF driven current of up to 30 kA at (100 kW, 2.5 GHz), exceeding the modelling predictions. At the FT-2 tokamak (R = 0.56 m, a = 0.08 m, Bt = 3 T, Ip = 30 kA) experiments with a traditional toroidally oriented grill revealed no strong dependence of the LHCD density limit on the H/D ratio in spite of LH resonance densities differing by a factor of 3. Microwave Doppler reflectometry (DR) at the Globus-M, and DR and heavy ion beam probe measurements at the tokamak TUMAN-3M (R = 0.53 m, a = 0.24 m, Bt = 1.0 T, Ip = 190 kA) demonstrated geodesic acoustic mode (GAM) suppression at the L to H transition. Observations at FT-2 using Doppler Enhanced Scattering showed that the GAM amplitude is anti-correlated both spatially and temporally to the drift turbulence level and electron thermal diffusivity. For the first time turbulence amplitude modulation at the GAM frequency was found both experimentally and in global gyrokinetic modelling. A model of the L–H transition is proposed based on this effect. The loss mechanisms of energetic ions' (EI) were investigated in the neutral beam injection (NBI) experiments on Globus-M and TUMAN-3M. Empirical scaling of the 2.45 MeV DD neutron rate for the two devices shows a strong dependence on toroidal field and plasma current justifying the Bt and Ip increase by a factor of 2.5 for the proposed upgrade of Globus-M. Bursts of ∼1 MHz Alfvenic type oscillations correlating with sawtooth crashes were observed in ohmic TUMAN-3M discharges. The possibility of low threshold parametric excitation of Bernstein and upper hybrid waves trapped in drift-wave eddies resulting in anomalous absorption in electron cyclotron resonance heating (ECRH) experiments in toroidal plasmas was identified theoretically. A novel method of radial correlation Doppler reflectometry is shown to be capable of measuring the turbulence wave-number spectrum in realistic 2D geometry. On the progress in design and fabrication of three diagnostics for ITER developed in the Ioffe institute is reported: neutral particle analysis, divertor Thomson scattering and gamma spectroscopy.

Signatures of nematic quantum critical fluctuations in the Raman spectra of lightly doped cuprates

We consider the lightly doped cuprates Y$_{0.97}$Ca$_{0.03}$BaCuO$_{6.05}$ and La$_{2-x}$Sr$_x$CuO$_4$ (with $x=0.02$,0.04), where the presence of a fluctuating nematic state has often been proposed as a precursor of the stripe (or, more generically, charge-density wave) phase, which sets in at higher doping. We phenomenologically assume a quantum critical character for the longitudinal and transverse nematic, and for the charge-ordering fluctuations, and investigate the effects of these fluctuations in Raman spectra. We find that the longitudinal nematic fluctuations peaked at zero transferred momentum account well for the anomalous Raman absorption observed in these systems in the $B_{2g}$ channel, while the absence of such effect in the $B_{1g}$ channel may be due to the overall suppression of Raman response at low frequencies, associated with the pseudogap. While in Y$_{0.97}$Ca$_{0.03}$BaCuO$_{6.05}$ the low-frequency lineshape is fully accounted by longitudinal nematic collective modes alone, in La$_{2-x}$Sr$_x$CuO$_4$ also charge-ordering modes with finite characteristic wavevector are needed to reproduce the shoulders observed in the Raman response. This different involvement of the nearly critical modes in the two materials suggests a different evolution of the nematic state at very low doping into the nearly charge-ordered state at higher doping.

Comparison of magnetron sputtering and gas aggregation nanoparticle source used for fabrication of silver nanoparticle films

Magnetron sputtering and gas aggregation sources are commonly used techniques for the preparation of metallic nanoparticles. In this study we compare both of these techniques used for the production of thin Ag nanoparticle films from the point of view of their morphology, topography and optical properties in dependence on the deposition time and substrate material. It is shown that in the case of sputter deposition, the morphology and optical properties of prepared films are dependent on the substrate material and deposition time and the resulting films are smooth with root-mean-square roughness 2nm. By contrast, films produced using gas aggregation source are considerably rougher (root-mean-square roughness 12nm) and consist of individual Ag nanoparticles. The deposition time affects in this case only the amount of nanoparticles on the surface and intensity of an anomalous absorption peak.

Ultrafast self-action of surface-plasmon polaritons at an air/metal interface

We investigate both theoretically and experimentally the nonlinear propagation of surface-plasmon polaritons (SPP) on a single air/metal interface. Inspired by nonlinear dielectric waveguide theory, we analytically derive a model that describes the nonlinear propagation of SPPs, thus bridging the description of plasmonic and dielectric waveguides. The model, the numerical simulations, and the experiments, which are carried out in the 100 fs regime, reveal that the SPP undergoes strong ultrafast self-action which manifests itself through self-induced absorption. Our observations are consistent with a large, bulk, third-order nonlinear susceptibility $({\ensuremath{\chi}}^{(3)})$ of gold and provide a self-consistent theory of self-action of SPPs at an air/metal interface. Experimentally, we find $\mathrm{Im}{{\ensuremath{\chi}}^{\ensuremath{-}(3)}}\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{2}/{\mathrm{V}}^{2}$. These findings have important implications in the nonlinear physics of plasmonics and metamaterials as they provide evidence that nonlinear absorption has a significant effect on the propagation of SPPs excited by intense optical pulses. This self-action is also expected to affect the anomalous absorption of light near subwavelength structures as well as the strength of desirable nonlinear processes such as third-harmonic generation and four-wave mixing, which will inevitably compete with nonlinear absorption.

Studying processes of crystallization and cation ordering in Eu2Hf2O7

Methods of local X-ray anomalous diffraction and X-ray absorption spectroscopy based on the interaction of synchrotron radiation with condensed matter have been used to study the processes of formation and evolution of the crystal structure in Eu2Hf2O7 powders. It has been shown that the isothermal annealing of the X-ray amorphous mixed hydroxide leads initially to the formation of nanocrystalline powders, which have a defect fluorite structure with a clearly pronounced nonequivalence of the local environment of the Eu3+ and Hf4+ cations. An increase in the temperature of heat treatment to ≥1200°C leads to the nucleation and growth of nanodomains with a superstructural cation ordering of the pyrochlore type inside the coarse crystallites of the defect fluorite and, finally, at T ≥ 1500°C, to the complete phase transition of the fluorite-pyrochlore type in the Eu2Hf2O7 system. In the pyrochlore Eu2Hf2O7 structure, there was for the first time revealed a simultaneous broadening of the shape of the L3 absorption edges of both hafnium and europium, which indicates a partial change in the symmetry of the nearest oxygen environment of both cations.

Numerical study of anomalous absorption of O mode waves on magnetic field‐aligned striations

AbstractSimple expressions that describe mode conversion and anomalous absorption of ordinary (O) mode waves injected at angles between the vertical and magnetic zenith to upper hybrid (UH) oscillations in the presence of field‐aligned density striations are presented. The absorption takes place in a region above the UH resonance layer where the striations allow trapped eigenmodes, leading to excitation of large‐amplitude UH waves. The derivation of the expressions is guided by dimensional analysis and numerical simulations. The results are relevant in interpreting high‐latitude heating experiments where anomalous absorption due to striations plays a crucial role.

Anomalous absorption of a lower hybrid wave in a plasma with density fluctuations

Anomalous absorption of a lower hybrid wave via mode coupling to short parallel wavelength density fluctuations in a magnetized plasma is investigated. The mode coupling produces a beat mode with the frequency of the lower hybrid wave but an enhanced parallel wave number. This mode is Landau damped on electrons. The oscillatory velocity associated with the beat mode couples with the density ripple to modify the density perturbation of the lower hybrid wave introducing anomalous resistivity. The anomalous resistivity increases with the normalized wave number of the density ripple.

Anomalous collisional absorption of laser pulses in underdense plasma at low temperature.

In a previous paper [M. Kundu, Phys. Plasmas 21, 013302 (2014)], fractional collisional absorption (α) of laser light in underdense plasma was studied by using a classical scattering model of electron-ion collision frequency ν(ei), where total velocity v=√[v(th)(2)+v(0)(2)] (with v(th) and v(0) as the thermal and the ponderomotive velocity of an electron) dependent Coulomb logarithm lnΛ(v) was shown to be responsible for the anomalous (unconventional) increase of ν(ei) and α(∝ν(ei)) with the laser intensity I(0) up to a maximum value about an intensity I(c) in the low temperature (T(e)<15eV) regime and a conventional ≈I(0)(-3/2) decrease when I(0)≫I(c). One may object that the anomalous increase in ν(ei) and α were partly due to the artifact introduced in lnΛ through the maximum cutoff distance b(max)∝v. In this work, we show similar anomalous increase in ν(ei) and α versus I(0) (in the low temperature and underdense density regime) with more accurate quantum and classical kinetic models of ν(ei) without using lnΛ, but with a proper choice of the total velocity dependent inverse cutoff length k(max)∝v(2) (classical) or k(max)∝v (quantum). For a given I(0)<5×10(14)Wcm(-2), ν(ei) versus T(e) also exhibits so far unnoticed identical anomalous increase as ν(ei) versus I(0), even if the conventional k(max)∝v(th)(2) or k(max)∝v(th) (without v(0)) is chosen. The total velocity dependent k(max) in the kinetic models, as proposed here, is found to explain the anomalous increase of α with I(0) measured in some earlier laser-plasma experiments.

Long-term aging of Ag/a-C:H:O nanocomposite coatings in air and in aqueous environment

Nanocomposite coatings of silver particles embedded in a plasma polymer matrix possess interesting properties depending on their microstructure. The film microstructure is affected among others also by the RF power supplied during the deposition, as shown by transmission electron microscopy. The optical properties are characterized by UV–vis–NIR spectroscopy. An anomalous optical absorption peak from the Ag nanoparticles is observed and related to the microstructure of the nanocomposite films. Furthermore, a long-term aging of the coatings is studied in-depth in ambient air and in aqueous environments. It is shown that the studied films are not entirely stable. The deposition conditions and the microstructure of the films affect the processes taking place during their aging in both environments.

Anomalous sound absorption in lattices of cylindrical perforated shells

This work reports the enhancement of sound absorption by sonic crystals slabs made of cylindrical perforated shells. These building units, with perforations of millimeter size, show small losses and cannot explain the strong absorption observed at some specific frequencies when the slabs consist of just a few number of rows. It is found that this phenomenon is due to a resonant Wood anomaly which occurs when the incident wave couples with a leaky guided mode supported by the slab. This effect results in an enhancement of the absorption, since the energy transferred to the guided mode travels within the slab, along a direction perpendicular to the incident one. Multiple scattering and finite element simulations give support to the proposed behavior, the transmittance results being in good agreement with experimental data previously reported.

Anomalous absorption, plasmonic resonances, and invisibility of radially anisotropic spheres

AbstractThis article analyzes the response of a sphere with radially anisotropic permittivity dyadic (RA sphere), in both the electrostatic and full electrodynamic settings. Depending on the values and signs of the permittivity components, the quasistatic polarizability of the RA sphere exhibits several very different interesting properties, including invisibility, field concentration, resonant singularities, and emergent losses. Special attention is given to the anomalous losses that appear in the case of certain hyperbolic anisotropy values. We show that their validity can be justified in a limiting sense by puncturing the sphere at the origin and adding a small imaginary part into the permittivity components. A hyperbolic RA sphere with very small intrinsic losses can thus have significant effective losses making it an effective absorber. With different choices of permittivities, the RA sphere could also perform as a cloak or a sensor. The Mie scattering results by an RA sphere are used to justify the quasistatic calculations. It is shown that in the small parameter limit the absorption efficiency of an RA sphere is nonzero for certain lossless hyperbolic anisotropies. The absorption and scattering efficiencies agree with the quasistatic calculations fairly well for spheres with size parameters up to 1/3.

Perfect Anomalous Absorption of TM Polarized Light in Metallic Grating Situated in Asymmetric Surroundings

In this paper, we predict an unexpected perfect optical absorption phenomenon of oblique-incident transverse magnetic polarized light in a metallic grating situated in asymmetric surroundings. Two physical processes result in the anomalous absorption: One is the total internal reflection at the grating's interface; another is the Fabry–Perot-like resonance supported in the grating's slits. For small filling factor grating $({\rm f} , the enhanced anomalous absorption only appears at grazing incidence with incident angle larger than 85 $^{\circ}$ ; however, if the filling factor is sufficiently large $({\rm f} > 0.9)$ , anomalous absorption is realizable only if the total internal reflection occurs. The influences of structural parameters, such as grating thickness, slits material on the anomalous absorption are investigated. Based on these properties, a plasmonic absorption device with a designed absorption line shape is proposed.

Photothermal Characterization of Thermochromic Materials for Tunable Thermal Devices

A detailed infrared study of the semiconductor-to-metal transition (SMT) in a vanadium dioxide \((\hbox {VO}_{2})\) film deposited on a silicon wafer is presented. The \(\hbox {VO}_{2}\) phase transition is studied in the mid-infrared (MIR) region by analyzing the transmittance and the reflectance measurements, and the calculated emissivity. The temperature behavior of the emissivity during the SMT puts into evidence the phenomenon of the anomalous absorption in \(\hbox {VO}_{2}\) which has been explained by applying the Maxwell-Garnett effective medium approximation theory, together with a strong hysteresis phenomenon, both useful to design tunable thermal devices. Photothermal radiometry has been applied in order to study the changes in the modulated emissivity induced by a laser. Experimental results show how the use of these techniques represent a good tool for a quantitative measurement of the optothermal properties of vanadium dioxide-based structures.

Soliton building from spontaneous emission by ring-cavity fiber laser using carbon nanotubes for passive mode locking

We investigate the generation of a chirped pulse in a single-mode, ring-cavity, erbium-doped fiber laser employing carbon nanotubes (CNTs) as a saturable absorber (SA). The pulse propagation is simulated using analytical methods to understand and quantify the role of multiple SA properties, particularly in the propa- gation dynamics of the laser pulse. The soliton solution is obtained on the basis of nonlinear effects, such as gain dispersion, second anomalous group-velocity dispersion, self-phase modulation, and two-photon absorption for a generalized nonlinear Schrodinger equation. The influences of the SA parameter in the range from 0.1 to 0.4 on the chirp, power, and width of the soliton are calculated. A stable, passively mode-locked fiber laser using CNTs as an SA is modeled. In addition, the power, width, chirp, and phase of the soliton pulses can be tuned by choosing suitable SA parameters. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.OE .54.1.011005)

Collisional excitation of vinylidene (H2CC)

Though H2CO, H2CS, H2CCC, H2CCCC, H2CCO have been identified in cool interstellar molecular clouds, identification of H2CC is still awaited. To analyze its spectrum, collisional rate coefficients are required. We have calculated collisional rate coefficients for rotational transitions between 23 levels of ortho and para H2CC for kinetic temperatures 10, 20, 30, 40, and 50K. The scattering problem is analyzed using the computer code MOLSCAT where the colliding partner is He atom. The interaction between H2CC and He has been calculated with GAUSSIAN 2003. For the interaction potential obtained with GAUSSIAN 2003, MOLSCAT is used to derive the parameters q(L,M,M′|E) as a function of energy E of the colliding partner. After averaging the parameters q(L,M,M′|E) over a Maxwellian distribution, the parameters Q(L,M,M′|T) as a function of the kinetic temperature T in the cloud are obtained. Finally, the collisional rate coefficients have been calculated.We have also calculated radiative transition probabilities for the transitions between the rotational levels. Finally, for ortho-H2CC, we have solved a set of statistical equilibrium equations coupled with the equations of radiative transfer and found that the H2CC may be identified through anomalous absorption of its transition 111–110 at 4.89GHz.

Anomalous water absorption by microelectronic encapsulants due to hygrothermal‐induced degradation

ABSTRACTEpoxy molding compounds are widely used as microelectronic encapsulants to protect the electronic circuitry from moisture. Since these compounds are hydrophilic they impose a reliability risk, which is assessed by lifetime tests. The interpretation of these tests is generally based on Fickian absorption. However, this work demonstrates that water absorption by microelectronic encapsulants shows anomalous behavior due to hygrothermal‐induced degradation of the material. Namely, experimental data show that the absorption by maiden samples is much slower than subsequent (de)sorption cycles, whereas the solubility depends on the highest water content that was reached in the history of the material. Moreover, at temperatures above glass transition the material might even physically decompose due to water exposure. Comparing these results with common theoretical models for anomalous water absorption shows that the experimental observed anomalies are most likely triggered by internal degradation of the encapsulant, which will impact the reliability assessment of epoxy encapsulated microelectronics. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41192.

活动星系核中的尘埃

Dust is the cornerstone of the unification theory of active galactic nuclei (AGNs). This theory proposes that all AGNs are essentially born equal: all types of AGNs are surrounded by an optically thick dust torus and are basically the same object but viewed from different lines of sight. The large diversity in the observational properties of AGNs is simply caused by the viewing-angle-dependent obscuration of the nucleus: those viewed face-on are unobscured (allowing for a direct view of their nuclei) and recognized as 1 AGNs, while those viewed edge-on are AGNs with most of their central engine and broad line regions being hidden by the obscuring dust. However, little is known about the dust in the circumnuclear torus of AGNs. There is evidence suggesting that the size and composition of the dust in AGNs may differ substantially from that of the Galactic interstellar dust, as reflected by the flat gray extinction curves, the 2175 A extinction bump is not (or at least rarely) seen in AGNs, and the anomalous silicate emission or absorption features observed respectively in type1 and type 2 AGNs. This review summarizes our current understanding of the extinction and infrared emission properties of the circumnuclear dust in AGNs as well as the inferred dust composition and size distribution.