Color screening,absorption, and σ tot pp at LHC

We show that a growth of the proton-proton total cross section with energy can be entirely attributed to the purely perturbative mechanism. The infrared regularization at rather short distances R _c ? 0.3 fm allows extending the BFKL technique from deep inelastic to hadron-hadron scattering. With the inclusion of the absorption corrections our results are in agreement with the LHC data on σ _tot ^pp .     

Nonlinear optical absorption and refraction in Ru, Pd, and Au nanoparticle suspensions

We present the results of studies of the nonlinear optical properties of Pd, Ru, and Au nanoparticles. We studied the nonlinear refraction and nonlinear absorption of suspensions of these nanoparticles at 1064-nm wavelength. A relatively strong nonlinear absorption of the Pd nanoparticles was observed in the case of 1064-nm, 50-ps pulses (β=2×10⁻⁹ m W⁻¹). The Ru and Pd nanoparticles showed weak negative nonlinear refraction (γ∼−(6–8)×10⁻¹⁶ m² W⁻¹) in this spectral range. In the case of the Au nanoparticles, a saturated absorption at 532 nm dominated over other nonlinear optical processes.     

Effect of coupling between linear absorption and nonlinear absorption on Z-scan measurements

The contribution of multiphoton absorption to open-aperture Z-scan measurements is analysed by coordinate transformation. The approximate closed-form solution is obtained, which is suitable for application in higher-optical power regime. As an example, the coupling between linear absorption and two-photon absorption is discussed in detail.     

Two-photon absorption and two-photon induced absorption of liquid toluene at 347.15 nm

Pump pulse transmission and time-delayed probe pulse transmission measurements through liquid toluene were performed with linear and circular polarized second harmonic pulses of a mode-locked ruby laser system. Two-photon absorption and two-photon induced absorption are observed. The induced absorption anisotropy is investigated. A theory of two-photon absorption in isotropic media is presented. The two-photon absorption cross-section components, the effective excited-state absorption cross-section, the absorption anisotropy relaxation time and the excited singlet-state relaxation time are determined.     

Partial absorption and “virtual” traps

The spatial probability distribution associated with diffusion and attenuation in partially absorbing media is studied. An equivalence is established between a system with free diffusion for x>0 and partial absorption for x<0, and a semi-infinite system (x>0) with a radiation boundary condition at x=0. By exploiting this equivalence, it is shown that the effect of a partially absorbing medium in the long-time limit is equivalent to that of a perfect, virtual trap whose size is smaller than the original absorbing medium. For short times, however, there is substantial penetration of diffusing particles into the absorber. The virtual trap approach is readily generalized to higher dimensions. This allows one to obtain the density profile of diffusing particles around a partially absorbing spherical trap. An unusual crossover between short-time penetration and long-time trapping occurs in two dimensions; the size of the virtual trap is exponentially small in the case of weak absorption, corresponding to an absorption time which is exponentially large.     

π-SCF and INDO calculations and the absorption,polarized excitation and circular dichroism spectra of [4]-helicenes

The absorption and circular dichroism spectra of (-)d-1,12-dimethyl-benzo[c]phenanthrene-5-acetic acid are reported, together with the polarized excitation and fluorescence spectra of the parent hydrocarbon, [4]-helicene. The transition energies of 1,12-dimethyl-[4]-helicene calculated in the π-SCF approximation, and the corresponding dipole and rotational strengths obtained by the dipole-velocity method, show that the optical isomer studied has the M-configuration with the stereochemical form of a segment of a left-handed helix. Analogous calculations in the INDO approximation using both the dipole-velocity and the dipole-length procedure with separate consideration of the one-centre and the two-centre transition moment integrals, indicate that the more satisfactory dipole and rotational strengths are obtained in the two-centre dipole-velocity formulation. The appearance of σ → π* transitions at higher energies limits the application of the π-SCF procedure, but the INDO method is found to place these transitions at too low an energy.     

Models of optical absorption in amorphous semiconductors at the absorption edge — A review and re-evaluation

Davis-Mott and Tauc models of optical absorption at the absorption edge in the high absorption coefficient region (10⁴cm^–1) are carefully reviewed with regard to their theoretical foundations, assumptions, mathematical derivations, and results. The full implications of these models are exploited, and it is found that the Davis-Mott model for negligible matrix elements between localised states could account for the cubic power law behaviour of with photon energy of some amorphous semiconductors such as a-Si. A fractional power law to find the optical band gapE _opt, of the form [ (–E _opt)^r; 2r3] based on Davis-Mott model is proposed in which the indexr can be a function of disorder. The Tauc model has further been extended to the case of negligible matrix elements between localised states, in which the same square power law for vs. with the same meaning of the optical gap as in the original Tauc model has resulted. A consideration of the case of unequal matrix elements for those transitions between localised states and those between extended states is also included. The meaning ofE _opt has been re-assessed and it is emphasized that it is an extrapolation of delocalised states to the zero of the density of states rather than a threshold energy for the onset of some kind of optical transitions.This paper is cordially dedicated to Professor C. A. Hogarth who taught us the Physics of amorphous materials.     

Effects of shape and dopant on structural,optical absorption,Raman, and vibrational properties of silver and copper quantum clusters: A density functional theory study

We investigate the effects of shape and single-atom doping on the structural, optical absorption, Raman, and vibra- tional properties of Ag13, Ag12CUl, CUl3, and Cul2Agl clusters by using the （time-dependent） density functional the- ory. The results show that the most stable structures are cuboctahedron （COh） for Ag13 and icosahedron （Ih） for CUl3, Agl2CUlcore, and Cul2Aglsur. In the visible-near infrared optical absorption, the transitions consist of the interband and the intraband transitions. Moreover, red shifts are observed as follows： 1） clusters change from Agl2CUlcore to Ag13 to Ag12Culsur with the same motifs, 2） the shapes of pure Agl3 and Agl2CUlcore clusters change from COh to Ih to decahe- dron （Dh）, 3） the shape of Agl2CUlsur clusters changes from Ih to COh to Dh, and 4） the shapes of pure CU13 and Cu12Agl clusters change from Ih to Dh to COb. All of the Raman and vibrational spectra exhibit many significant vibrational modes related to the shapes and the compositions of the clusters. The ranges of vibrational spectra of Ag13, Agl2CUl or CU13, and Cu12Agl clusters become narrower and the vibrational intensities increase as the shape of the clusters changes from Ih to Dh to COh.     

Two- and three-photon absorption in a novel fluorene-based compound

A novel symmetrical charge transfer fluorene-based compound 2,7-bis (4-methoxystyryl)-9, 9-bis (2-ethylhexyl)-9H-fluorene (abbreviated as BMOSF) was synthesized and its nonlinear absorption was investigated using two different laser systems: a 140-fs, 800-nm Ti:sapphire laser operating at 1-kHz repetition rate and a 38-ps, 1064-nm Nd:YAG pulsed laser operating at 10-Hz repetition rate, respectively. Unique nonlinear absorption properties in this new compound were observed that rise from multiphoton absorption. The nonlinear absorption coefficients were measured to be 6.02×10-3 cm/GW (due to two-photon absorption, exciting wavelength is 800 nm) and 3.6×10-20 cm3/W2 (due to three-photon absorption, exciting wavelength is 1064 nm). This new compound possesses strong fluorescence induced by two-photon absorption and obvious three-photon absorption optical limiting effects.     

X-ray absorption spectroscopy in biology – present and future

From May 10 to 12, the GISAXS Workshop 2005 was hosted at HASYLAB/DESY in Hamburg, Germany. GISAXS stands for Grazing Incidence Small Angle X-ray Scattering, a surface-sensitive technique to observe structures on large length scales up to several hundred nanometers. Organized by R. Gehrke and S. V. Roth from HASYLAB and P. Müller-Buschbaum from University of Technology Munich, the workshop attracted more than 50 participants from all over the world, originating a very stimulating atmosphere with invited talks, a contributed poster session and practical training, including real data acquisition at the beamline BW4.     

Enhanced luminescent properties and optical absorption of γ-irradiated KI: Ce, Tb crystals

This paper reports that KI doped with Ce³⁺ or double doped with Tb³⁺ and Ce³⁺ were prepared by the Bridgman-Stockbarger method and characterized by optical absorption photoluminescence (PL), thermoluminescence (TL), photostimulated emission (PSL) and TL emission. The optical absorption measurement indicates that F and V₁, V₂ centers are formed in the crystals during the γ irradiation process. It was attempted to incorporate a broad band of Ce³⁺ activator into the narrow band emission of Tb³⁺ in the KI host without the reduction of emission intensity. Ce³⁺-co-doped KI and Tb crystals showed a broad band emission due to the d-f transition of Ce³⁺ and a reduction in the intensity of emission peaks due to the ⁵D₃-⁷F_j (j=3,4,5,6) transition of Tb³⁺, when they were excited at 240 nm.These results supported that an effective energy transfer occurs from Tb³⁺ to Ce³⁺ in the KI host. Co-doping Ce³⁺ ions greatly intensified the excitation peak at 260 nm for the emission at 393 nm of Tb³⁺, which means that more lattice defects, involved in the energy absorption and transfer to Tb³⁺, are formed by the Ce³⁺ co-doping. The integrated light intensity is an order of magnitude higher as compared to the undoped samples for similar doses of irradiation and heating rates. The defects generated by irradiation were monitored by optical absorption and TSL Trap parameters for the TL process are calculated and presented.     

Ultra-violet absorption spectra and π-electron structures of nitromethane and the nitromethyl anion

The ultra-violet absorption spectrum of nitromethane was measured under various conditions. Besides the weak band at 270 mμ, a strong band, which may be regarded as due to the longest wavelength π→π* transition band, was observed at 198 mμ in the gaseous state. Further, the absorption spectrum of nitromethane was measured in aqueous solutions with several different ph values, and a strong band was observed at 233 mμ. From the fact that the pK_a value evaluated on the basis of the ph dependence of the absorption intensity is equal to that obtained electrometrically, it was concluded that the 233 mμ band is to be ascribed to the nitromethyl anion (H₂C^-NO₂). This band was found to shift to 238 mμ in alcoholic KOH solution.

The π-electron structure of the anion was studied theoretically by taking into account configuration interaction in terms of the ground, charge transfer, and locally excited configurations. It is shown that the 233 mμ band of the anion may be interpreted as an intramolecular charge-transfer absorption involving a large electron transfer from CH₂ ^- toward NO₂. It is suggested that electron donating substituent groups like NH₂, OH, and CH₂ ^- should cause the 198 mμ band of the nitro group to shift toward shorter wavelengths, in marked contrast to the case of substituted benzene molecules like aniline and phenol.     

γ-MnO2/polyaniline composites: Preparation, characterization, and applications in microwave absorption

MnO₂/doped polyaniline (PANI) is prepared by an in situ polymerization method using γ-MnO₂ as the addition agent and hydrochloric acid as the doping agent. Products are characterized by FT-IR, UV-vis, XRD, and TEM. Conductivity, electromagnetic properties, and microwave absorption properties are first discussed on the basis of structural characterization. The as-prepared products of MnO₂/PANI are partially crystalline in nature and spherical in pattern with grain sizes of 50-70 nm. MnO₂ particles are successfully decorated with doped PANI. MnO₂/PANI displays moderate electric conduction, excellent dielectric losses, and microwave absorption capabilities. Compared to pure MnO₂, the dielectric and reflection loss properties of MnO₂/PANI composites exhibit significant improvements, with an effective absorption band at 5 GHz under −10 dB and maximum reflection loss of −21 dB at 13.56 GHz. Pure MnO₂ shows an effective absorption band of 3 GHz under −10 dB and a maximum reflection loss of −14.20 dB at 11.5 GHz. Thus, MnO₂/PANI composites are found to be a promising microwave absorption material.     

Fundamental absorption of calcium,magnesium, and lithium fluorides in the range of 8–12 μm

The fundamental absorption of calcium, magnesium, and lithium fluorides in the range of 8–12 μm has been studied experimentally by the spectrophotometric method. The known and experimentally obtained values of the absorption coefficients of these materials have been analyzed. It has been shown that the values experimentally measured in the range of 8–12 μm obey the Uhrbach rule and the multiphoton absorption determines the long-wavelength transmission cutoff of pure optical materials. The results presented make it possible to suggest that plates made of LiF and CaF₂ crystals and of optical ceramics based on MgF₂ can be used to fabricate calibrated radiation attenuators in the spectral range of 8–12 μm.     

EPR, optical absorption and superposition model study of Fe³(+) doped strontium nitrate single crystals

Electron paramagnetic resonance (EPR) study of Fe3(+) ions doped strontium nitrate (SN) single crystals is performed at liquid nitrogen temperature and at X band frequency. The spin Hamiltonian (SH) parameters are determined from the resonance lines observed at different angular rotations. The crystal field parameters (CFPs) are evaluated using superposition model of Newman. The Zeeman g-factor and zero-field splitting parameters (ZFSPs) of Fe3(+) ion in SN (truncated SH considered) are: g=1.9989 ± 0.002 and ∣D∣=(338 ± 5) × 10?? cm?1, ∣E∣=(10 ± 5)× 10?? cm?1, a=(458 ± 5)× 10?? cm?1, respectively. The Fe3(+) ion enters the lattice substitutionally replacing the Sr2(+) sites of cubic symmetry. The local site symmetry of Fe3(+) ion in the crystal is orthorhombic (lower than that of the host). The optical absorption study of the crystal is also done at room temperature in the wavelength range 195-925 nm. The energy values of different orbital levels are determined. The observed bands are assigned as transitions from the (6)A?(g)(S) ground state to various excited states of Fe3(+) ion in a cubic crystal field approximation. The observed band positions are fitted with four parameters, the Racah interelectronic repulsion parameters (B and C), the cubic crystal field splitting parameter (Dq) and the Trees correction (α) yielding: B=934, C=2059, Dq=1450, and α=90 (in cm?1). On the basis of EPR and optical data, the nature of metal-ligand bonding in this crystal is discussed. The ZFSPs are also determined theoretically using microscopic SH theory based on perturbation theory and CFPs, B(kq) obtained from superposition model. The values of ZFSPs thus obtained are ∣D∣=(340 ± 5) × 10?? cm?1 and ∣E∣=(15 ± 5) × 10?? cm?1.     

Microstructure and optical absorption of Au-MgF2 nanoparticle cermet films

The microstructure and optical absorption of Au-MgF2 nanoparticle cermet films with different Au contents are studied. The microstructural analysis shows that the films are mainly composed of the amorphous MgF2 matrix with embedded fcc Au nanoparticles with a mean size of 9.8-21.4nm. Spectral analysis suggests that the surface plasma resonance （SPR） absorption peak of Au particles appears at λ=492-537nm. With increasing Au content, absorption peak intensity increases, profile narrows and location redshifts. Theoretical absorption spectra are calculated based on Maxwell-Garnett theory and compared with experimental spectra.     

K − absorption in nuclei by two and three nucleons

It will be shown that the peaks in the (Λp) and (Λd) invariant mass distributions, observed in recent FINUDA experiments and claimed to be signals of deeply bound kaonic states, are naturally explained in terms of K ^? absorption by two or three nucleons leaving the rest of the original nuclei as spectator. For reactions on heavy nuclei, the subsequent interactions of the particles produced in the primary absorption process with the residual nucleus play an important role. Our analyses leads to the conclusion that at present there is no experimental evidence of deeply bound K ^? state in nuclei. Although the FINUDA experiments have been done for reasons which are not supported a posteriori, some new physics can be extracted from the data.     

Numerical and experimental study on sound absorption by pseudostochastic diffusors

I.IntroductionPseudostochasticdiffusorisaperiodicsurfacestructurewhichconsistsofaseriesofwellsofthesamewidthbutofdifferentdepths,whicharedeterminedaccordingtoapseudthrandomsequence(forexample,quadraticresiduesequence).ItisverifiedfromtheoryandexPerimelltthatthescatteredenergyfromthestructureplaneisindependentofangle.Intheotherhand,theunexpectedhighsoundabsorptionparticularlyatIowfrequencieswasreported.Severalauthorsattemptedtoexplainthephysicalmechanism,however,thesatisfiedpredicationhasnotb…     

Broadband and tunable terahertz absorption via photogenerated carriers in undoped silicon

Terahertz absorbers based on doped silicon have achieved broadband and high-efficiency absorption due to their high concentration of carriers.However,their tunable performance is obviously insufficient.Here,we propose a new scheme for active terahertz absorption based on undoped silicon with a metamaterial antireflection layer,which realizes both strong absorption and ultrahigh modulation depth.Benefiting from the weak absorption and high transmission of undoped silicon for 1064-nm continuous wave,uniformly distributed carriers across the entire thickness of the absorber are excited,and efficient free carrier absorption of the terahertz wave is obtained.We use only a 500-μm thick absorber and achieve absorption greater than 90%in the range of 0.58 to 1.92 THz,with a peak value of 99%.More important,the absorber can be switched between two working states of nonabsorption and high-efficiency absorption by changing the pump power,which means the modulation depth reaches 100%.This simple and high-performance implementation scheme provides a new idea for the design of terahertz tunable absorbers.     

TheJ/Ψ absorption cross section in nuclei and color screening

Data on 120 GeV photoproduction ofJ/'s in nuclear targets are re-examined to extract the absorption cross section forJ/'s in high energy collisions with nucleons. We find _a =6.6±2.2 mb in contrast with an earlier estimate of 1–2 mb. Comparison of low and high energy data on photon producedJ/'s thus no longer show possible evidence for observable effects of color screening. Examination of representative data on the Feynmanx distributions ofJ/ production by hadrons demonstrates how to extract both the total inelasticJ/-nucleon cross section and the partial cross section into open charm. We find that the data is inconsistent with any significant contribution from color screening.