Anomalous Absorption Research Articles

Possible origin of the anomalous far-infrared absorption by small metal particles

We carried out the far-infrared transmission measurements on the ligand stabilized Au55 particles dispersed in CsI. We found that the far-infrared absorption coefficient recovers the ω2-dependence (the same behavior as the classical electric dipole-like absorption) for frequencies above the crossover energy Ec=ℏ2/2mea2∼160cm−1 (a=particle radius) while the absorption coefficient below Ec, which arises from the transitions of the electrons between the discrete energy levels, saturates to a value ∼4cm−1 at ω∼Ec. Since Ec of the small metal particles (a>20Å) studied in the past falls well below the lowest frequency typically accessible for the far-infrared spectroscopy (ω∼20cm−1), we conclude that all the previously measured far-infrared absorption must have been an extension of the absorption of the quantum regime set at Ec, making the absorption measured in the typical far-IR window (20cm−1<ω<120cm−1) anomalously large when compared with the classical electric dipole absorption by the same size particles.

Use of the WiNRADiO G305e scanning receiver in the riometer for measuring the anomalous absorption of cosmic radio radiation

A method for measuring the radio noise absorption by the ionosphere and a device—a riometer—developed on its basis are described. The idea behind the device is to record the cosmic radio radiation power at several close frequencies from the band in use. A commercially produced WiNRADiO G305e radio receiver is used in the riometer. The measurement technique allows one to tune out narrowband noise, improving thereby the quality of riometric observations. The riometer is located at the Lovozero observatory of the Polar Geophysical Institute (Kola Research Center, Russian Academy of Sciences). This device is distinguished by the simple design, high reliability, and ease in operation.

Effect of anomalous absorption of neutrons undergoing Laue diffraction at Bragg angles close to π/2

A direct experimental observation of the anomalous absorption of neutrons undergoing Laue diffraction in a highly perfect silicon single crystal of size about 200 mm at Bragg angles close to π/2 is reported. It is shown that, in the case of diffraction at the (220) plane, the neutron absorption length may be several meters, which is nearly one order of magnitude longer than the mean absorption length for neutrons of the same wavelength. This circumstance makes it possible to study effects accompanying Laue diffraction at Bragg angles of up to 88° and a crystal size of about 200 mm.

On the transition between complementary medium and zero-refractive-index medium

It is known that “complementary media” which are constructed as slabs that optically cancel each other have optical properties that are different from materials with a zero refractive index. However, a zero-refractive-index material can be viewed as a special case of complementary media in which the constitutive parameters go to zero. This apparent inconsistency is resolved as we find that the optical property of a system can change from complementary-like to a zero-index–like as the system parameters change when absorption is considered properly and there is an intermediate regime in which the complementary system absorbs half of the incident light. The physical reason underlying this anomalous absorption is explained.

Importance of collisional rates for anomalous absorption in H2CC molecule

Formaldehyde (H2CO) is the first organic molecule identified in a number of galactic and extragalactic sources. It was identified through its transition 110–111 at 4.829GHz in absorption. Later on, this transition of formaldehyde was found as showing anomalous absorption in the direction of four dark nebulae. Anomalous absorption is an unusual phenomenon. Structure of H2CC is very similar to that of H2CO and H2CS. Both H2CO and H2CS have already been identified in a number of cosmic objects. Since cosmic abundance of carbon is 20 times larger than that of sulfur, we propose that H2CC may be identified in cool cosmic objects through its transition 110–111 at 4.85GHz. Keeping in view of the similarity of energy levels of H2CC with H2CO, in the present investigation we have performed calculations for three sets of collisional rates for rotational transitions in ortho-H2CO due to collisions with (i) He atom, (ii) ortho-H2 (J=1), and (iii) para-H2 (J=0). All the three sets of calculations showed the anomalous absorption of 110–111 transition of H2CC. However, the anomalous absorption of 211–212 transition is found to be weak.

Anomalous absorption of electromagnetic waves of the 10-cm wavelength band in water

Results of investigations of propagation of electromagnetic waves in water are presented. It is shown that, in the frequency range around 2800 MHz, anomalous energy absorption is observed. The experimental results obtained by the authors and the published data obtained by other researchers are justified.

On the possibility of low-threshold anomalous absorption in tokamak 2nd-harmonic electron cyclotron resonance heating experiments

The parametric decay of an extraordinary electron cyclotron pump wave to electron Bernstein (EB) wave and ion Bernstein wave leading to anomalous absorption in 2nd-harmonic electron cyclotron resonance heating (ECRH) experiments is analyzed. It is shown that in an axisymmetric system, like tokamak, excitation of the low-threshold absolute parametric decay instability (PDI) is possible in the case of non-monotonic behaviour of plasma density in radial direction and due to poloidal magnetic-field inhomogeneity. The threshold of the absolute PDI instability determined by linear dissipation of the EB wave is shown to be substantially exceeded in nowadays 2nd-harmonic ECRH experiments in tokamaks that provide an explanation for the mysterious ion acceleration effect observed there.

Importance of collisional rates for anomalous absorption in H2CO molecule

Formaldehyde (H2CO) is the first organic molecule identified in a number of galactic and extragalactic radio sources through its transition 110–111 at 4.830GHz in absorption. Later on, this transition was found in anomalous absorption. In some cosmic objects, this transition however was found in emission and even as a maser radiation. Since the transition 110–111 of ortho-H2CO is considered as a unique probe of high density gas at low temperature, the study of H2CO has always been of great importance for astrophysicists as well as for spectroscopists. In view of the availability of better input data required for such investigation, it is worth while to investigate again about the radiations from ortho-H2CO. In the present study, we have investigated anomalous absorption of 110–111, 211–212 and 312–313 transitions of ortho-H2CO. The present results are more reliable as compared to those obtained earlier.

Photoelectrochemical study of ZnSe electrodeposition on Cu electrode

The paper describes the photoelectrochemical studies and the electrochemical synthesis of zinc selenide thin films. Obtained results specify the range of potentials where semiconducting compound is deposited. Photocurrent profiles indicate the p-type conductivity of the electrodeposited semiconductor. The generated photocurrent indicates the anomalous absorption of the light below the band gap range of ZnSe and suggests a plasmon–exciton coupling effect.

On the interference absorption of X-rays in crystals with weak deformations

The problem of Borrmann absorption (anomalous absorption) of X-rays in weakly deformed crystals is considered on the basis of Takagi’s approach to the dynamical theory. Using wave function considerations, the attenuation of rays is represented by exp(−σl) where the attenuation factor σ includes a parameter of the lattice deformation field. The possibility of cases σ = 0 and even σ < 0 is discussed.

In Situ Anomalous Small-Angle X-ray Scattering and X-ray Absorption Study of Fuel Cell Catalysts

not Available.

Three-dimensional simulations of anomalous absorption of laser radiation by plasma with supercritical density

A three-dimensional (3D) model of the interaction of laser radiation with plasma in the framework of Maxwell-Vlasov equations has been used to calculate the anomalous optical absorption in plasma of supercritical density. The results of calculations confirmed the development of anomalous absorption that was previously revealed by 2D models, which were insufficient for comparison to the experiment. Calculations were performed for a system containing about 106 macroparticles that allowed the absorption coefficient and other characteristics of anomalous absorption in plasma with an inhomogeneous surface to be determined as functions of various parameters of the incident radiation and plasma target. Results are analyzed and estimations are obtained for the contributions of ionization processes and pair collisions of electrons, which show that these factors were quite reasonably ignored in the model. All quantitative results are obtained for the third harmonic of neodymium laser (λ = 0.351 μm) at a tenfold excess of the substance density over a critical value for this radiation.

Description of anomalous Zeeman patterns in stellar astrophysics

The influence of a magnetic field on the broadening of spectral lines and transition arrays in complex spectra is investigated. The anomalous absorption or emission Zeeman pattern is a superposition of many profiles with different relative strengths, shifts, widths, asymmetries and sharpnesses. The "sigma" and "pi" profiles can be described statistically, using the moments of the Zeeman components. We present two statistical modellings: the first one provides a diagnostic of the magnetic field and the second one can be used to include the effect of a magnetic field on simulated atomic spectra in an approximate way.

Optical properties of X-rays – dynamical diffraction

The first attempts at measuring the optical properties of X-rays such as refraction, reflection and diffraction are described. The main ideas forming the basis of Ewald‘s thesis in 1912 are then summarized. The first extension of Ewald‘s thesis to the X-ray case is the introduction of the reciprocal lattice. In the next step, the principles of the three versions of the dynamical theory of diffraction, by Darwin, Ewald and Laue, are given. It is shown how the comparison of the dynamical and geoämetrical theories of diffraction led Darwin to propose his extinction theory. The main optical properties of X-ray wavefields at the Bragg incidence are then reviewed: Pendellösung, shift of the Bragg peak, fine structure of Kossel lines, standing waves, anomalous absorption, paths of wavefields inside the crystal, Borrmann fan and double refraction. Lastly, some of the modern applications of the dynamical theory are briefly outlined: X-ray topography, location of adsorbed atoms at crystal surfaces, optical devices for synchrotron radiation and X-ray interferometry.

Anomalous phenomena in ECRH experiments at toroidal devices and low-threshold parametric decay instabilities

In the paper the possibility of total 3D trapping of electron Bernstein ( EB) waves in the tokamak equatorial plane in the vicinity of the local density maximum produced by electron pump -out-effect is demonstrated. Thresholds and growth rates of the associated absolute (temporally growing) parametric decay instability (PDI) leading to anomalous absorption ispredicted in the range of less than 10 0 kW.Itspossible role inexplanation of ion acceleratio n observed inECRH experiments as well as in redistribution of the deposited power is discussed .

Optical properties of X-rays – dynamical diffractionThis Laue centennial article has also been published inZeitschrift für Kristallographie[Authier (2012).Z. Kristallogr.227, 36–51

The first attempts at measuring the optical properties of X-rays such as refraction, reflection and diffraction are described. The main ideas forming the basis of Ewald's thesis in 1912 are then summarized. The first extension of Ewald's thesis to the X-ray case is the introduction of the reciprocal lattice. In the next step, the principles of the three versions of the dynamical theory of diffraction, by Darwin, Ewald and Laue, are given. It is shown how the comparison of the dynamical and geometrical theories of diffraction led Darwin to propose his extinction theory. The main optical properties of X-ray wavefields at the Bragg incidence are then reviewed: Pendellösung, shift of the Bragg peak, fine structure of Kossel lines, standing waves, anomalous absorption, paths of wavefields inside the crystal, Borrmann fan and double refraction. Lastly, some of the modern applications of the dynamical theory are briefly outlined: X-ray topography, location of adsorbed atoms at crystal surfaces, optical devices for synchrotron radiation and X-ray interferometry.

Anisotropic optical response of the mixed-valent Mott-Hubbard insulator NaCu2O2

We report the results of a comprehensive spectroscopic ellipsometry study of NaCu2O2, a compound composed of chains of edge-sharing Cu2+O4 plaquettes and planes of Cu1+ ions in a O-Cu1+-O dumbbell configuration, in the spectral range 0.75-6.5 eV at temperatures 7 -300 K. The spectra of the dielectric function for light polarized parallel to the Cu1+ planes reveal a strong in-plane anisotropy of the interband excitations. Strong and sharp absorption bands peaked at 3.45 eV (3.7 eV) dominate the spectra for polarization along (perpendicular) to the Cu2+O2 chains. They are superimposed on flat and featureless plateaux above the absorption edges at 2.25 eV (2.5 eV). Based on density-functional calculations, the anomalous absorption peaks can be assigned to transitions between bands formed by Cu1+ 3dxz(dyz) and Cu2+ 3dxy orbitals, strongly hybridized with O pstates. The major contribution to the background response comes from transitions between Cu1+ 3dz2 and 4px(py) bands. This assignment accounts for the measured in-plane anisotropy. The dielectric response along the Cu2+O2 chains develops a weak two-peak structure centered at 2.1 and 2.65 eV upon cooling below 100 K, along with the appearance of spin correlations along the Cu2+O2 chains. These features bear a striking resemblance to those observed in the single-valent Cu2+O2 chain compound LiCuVO4, which were identified as an exciton doublet associated with transitions to the upper Hubbard band that emerges as a consequence of the long-range Coulomb interaction between electrons on neighboring Cu2+ sites along the chains. An analysis of the spectral weights of these features yields the parameters characterizing the on-site and long-range Coulomb interactions.

Anomalous microwave absorption in multi-walled carbon nanotubes filled with iron

The interaction of millimeter-wave radiation (MWR) with vertically oriented carbon nanotubes filled with iron (Fe-MWCNT) in solid monolith has been investigated. Fe-MWCNT demonstrated high-efficiency towards electromagnetic shielding due to a high conductivity of CNT and iron-containing filling compound. The shielding efficiency and the reflection loss depending on the CNT orientation have been measured in a rectangular waveguide. A resonant absorption of millimeter waves has been revealed with the orthogonal Fe-MWCNT orientation with respect to the MWR electric field in the waveguide.

Anomalous optical conductivity in disordered condensed matter

The real and imaginary optical conductivities in disordered semiconductors (and metals) do not follow classical Drude's law in the near infrared region. We discuss an origin of the anomalous free carrier absorption in metallic (and near metallic) states of chalcogenide materials (phase-change GST), dye-sensitized nanocrystalline TiO2 and nanocrystalline silicon films. A series sequence of “localized” and “extended” state type behavior of carriers produces a Lorentz-type resonance which is caused by “bound” (localized) electrons. The analytical expressions were fit to the experimental data and produced various important physical parameters such as the numbers of free and localized carriers, the scattering time of free carriers, tunneling time of localized carriers, and the Drude dc conductivity in the system. We also discuss whether the present model has generated reasonable physical parameters.

Investigation of the Low-Frequency Vibrations of Crystalline Tartaric Acid Using Terahertz Spectroscopy and Solid-State Density Functional Theory

The room temperature and cryogenic terahertz (THz) spectra (10-95 cm(-1)) of l-tartaric acid and dl-tartaric acid were investigated. At 293 K, the l-tartaric acid spectrum showed four absorption features at 36.4, 61.6, 78.7, and 87.3 cm(-1) in the experimental spectrum. Once cooled to 78 K, these features narrowed and shifted to 35.9, 63.4, 81.1, and 90.1 cm(-1). The THz spectrum of dl-tartaric acid is significantly different, containing only a single absorption at 79.9 cm(-1) at room temperature, which shifts to 82.9 cm(-1) at 78 K. Solid-state density functional theory calculations [B3LYP/6-311G(2d,2p)] were performed to simulate the crystalline structure of both molecular solids and to assign the observed spectral features to specific atomic motions. The THz spectrum of l-tartaric acid is particularly interesting in that it contains a theoretically unaccounted for spectral feature that may arise from second-order phonon processes and also exhibits an anomalous red-shifting absorption feature with cooling that is shown to originate from negative thermal expansion of the crystal.