Ratio Of Absorption Cross Section Research Articles

Pair production in Reissner-Nordström-Anti de Sitter black holes * *Supported by the National Natural Science Foundation of China (11675272), the Ministry of Science and Technology of the R.O.C. under the grant MOST 108-2112-M-008-007, National Research Foundation of Korea (NRF) funded by the Ministry of Education (2019R1I1A3A01063183)

We studied the pair production of charged scalar particles of a five-dimensional near extremal Reissner-Nordström-Anti de Sitter (RN-AdS5) black hole. The pair production rate and the absorption cross section ratio in full spacetime are obtained and are shown to have a concise relation with their counterparts in the near horizon region. In addition, the holographic descriptions of the pair production, both in the IR CFT in the near horizon region and the UV CFT at the asymptotic spatial boundary of the RN-AdS5 black hole, are analyzed in the AdS2/CFT1 and AdS5/CFT4 correspondences, respectively. This work gives a complete description of scalar pair production in a near extremal RN-AdS5 black hole.

Investigation of the absorption Ångström exponent and its relation to physicochemical properties for mini-CAST soot

In this work, a mini-CAST soot generator was used to produce soot with different optical and physicochemical characteristics. Absorption Ångström exponents (AAE) expressing the absorption wavelength dependence were assessed by multiwavelength in-situ and filter-based (aethalometer) laser extinction. The two optical techniques showed good agreement. For the chosen mini-CAST operating conditions, AAEs between 1 and 3.5 were found. Soot with high mass-fractions of organic carbon (OC) and pyrolytic carbon (PC) determined with thermal optical analysis were associated with AAEs significantly higher than 1. Heating to 250 and 500°C removed the majority of polycyclic aromatic hydrocarbons. However, the thermal-optical analysis revealed that OC and PC were abundant in the soot with AAE > 2 also after heating the aerosol. Analysis of mass absorption cross section ratios for elemental carbon and OC indicated that elevated AAEs also after heating to 500°C could be related to persistent OC and PC components and/or the refractory soot. By comparing the mini-CAST soot optical properties with soot properties derived from in-situ extinction measurements in a premixed flame, mini-CAST soot with a higher AAE could be identified as less mature soot.Copyright © 2018 The Authors

Pair production of scalar dyons in Kerr–Newman black holes

We study the spontaneous pair production of scalar dyons in the near extremal dyonic Kerr–Newman (KN) black hole, which contains a warped AdS3 structure in the near horizon region. The leading term contribution of the pair production rate and the absorption cross section ratio are also calculated using the Hamilton–Jacobi approach and the thermal interpretation is given. In addition, the holographic dual conformal field theories (CFTs) descriptions of the pair production rate and absorption cross section ratios are analyzed both in the J-, Q- and P-pictures respectively based on the threefold dyonic KN/CFTs dualities.

Scalar Dyon Production In Near Extremal Kerr-Newman Black Holes

The pair production of charged scalar dyons is analytically studied in near-extremal Kerr-Newman (KN) dyonic black holes. The pair production rate and its thermal interpretation are given. Moreover, the absorption cross section ratio has been compared with the two-point function of the conformal field theories (CFTs) holographically dual to the near horizon geometry, namely warped AdS3, of the near extremal Kerr-Newman black holes to verify the threefold dyonic KN/CFTs correspondence.

Saturable absorption in one-dimensional Sb2Se3 nanowires in the visible to near-infrared region.

One-dimensional (1D) free-standing nanowires are particularly important for carrier confinement in two dimensions, which provides a platform to explore the nonlinear optical phenomena at the nanoscale. In this Letter, we demonstrate saturable absorption in the resonant and above-bandgap excitations of both ns and fs pulses in 1D crystalline Sb2Se3 nanowires prepared by the facile hydrothermal method. Impressively, the average length of the nanowires extends to a few micrometers with a high aspect ratio of 300. The excited-state to ground-state absorption cross-section ratio in Sb2Se3 nanowires is ≈0.23, which suggests that they can be utilized as passive mode lockers.

Spinor particle creation in near extremal Reissner–Nordström black holes

The pair production of spinor particles, which can be captured by the solution of the Dirac equation with an appropriate boundary condition, in charged black holes is investigated. We obtain the closed form of the production rate in the near extremal limit of Reissner–Nordström black holes. The cosmic censorship conjecture is seemingly guaranteed by the pair production process. Moreover, the absorption cross section ratio and retarded Green’s functions of the spinor fields calculated from the gravity side match well with those of spinor operators in the dual conformal field theory (CFT) side.

Soot maturity and absorption cross sections

We used time-resolved laser-induced incandescence (LII) to compare optical and physical properties of soot at the edge and in the center of two co-flow diffusion flames in common use for soot optical-diagnostics development. We made these measurements over a wide range of laser fluences using a laser wavelength of either 532 or 1064nm. Our results, combined with the previous results, suggest that the 532:1064nm absorption cross-section ratio is ≤1.8 for mature soot and increases with increasing hydrogen content and decreasing soot maturity. The absolute absorption cross sections at 532 and 1064nm, on the other hand, increase with soot maturity. Differences in the signal decay rates between center and edge regions further suggest that the thermal-accommodation coefficient decreases with increasing soot maturity. These results were analyzed using an energy- and mass-balance model that accounts for the effects of soot maturity on the absorption cross section, thermal-accommodation coefficient, and particle density. Given the sensitivity of LII to these parameters, it may be possible to use a combination of in situ measurements of pulsed LII fluence curves and temporal profiles to gain information about soot maturity.

Poly methyl methacrylate films containing metallophthalocyanines in the presence of CdTe quantum dots: Non-linear optical behaviour and triplet state lifetimes

Non-linear optical (NLO) parameters were determined for phthalocyanine complexes containing In, Ga and Zn as central metals when embedded in poly (methyl methacrylate) polymer in the absence and presence of quantum dots (QDs) in an effort to create the most optimal optical limiting material. The QDs employed were CdTe–TGA (TGA=thioglylcolic acid). Triplet lifetimes generally increased as the value of the ratio of absorption cross sections of the excited state to that of the ground state (k) decreased on addition of CdTe–TGA to the phthalocyanines. The saturation energy density (Fsat) values were generally smaller in the films when compared to the solutions. Fsat, Ilim, Im[χ(3)]/α and γ all gave values which were of optimal range (i.e. the Im[χ(3)]/α and γ values were high enough to ensure adequate optical limiting but not too high to make the compounds behave like optical filters. Also, the Fsat and Ilim values were small enough to mean that the optical limiting process started at an intensity which was not too high) for complex 10 containing Zn central metal and tetrasubstituted with amino groups.

Photonic spectral modulation in bacteriorhodopsin molecules and optimization of signal wavelength

In general, in excited-state absorption (ESA) based all-optical light modulator, maximum signal intensity modulation is achieved at the wavelength corresponding to maximum excited to ground state absorption cross-section ratio. However, theoretical analysis of photonic spectral modulation of broadband signal beam based on ESA in bacteriorhodopsin (BR) provides counterintuitive interesting results in the signal wavelength region 460–700nm. It is shown that the signal modulation is enhanced significantly at some particular wavelength values (optimum signal wavelength). Optimum signal wavelength in the region 450–700nm, varies with modulating intensity, and does not correspond to the peak absorption wavelength of the longer lived intermediate states. Present analysis is very useful in designing ESA based power efficient photonic devices.

Reprint of: Quantum yield of chlorine-atom formation in the photodissociation of chlorine peroxide (ClOOCl) at 308 nm

The production of Cl atoms in the laser flash photolysis of ClOOCl at 308nm has been investigated by time-resolved atomic resonance fluorescence at 235K. A value of ϕ=1.03±0.12 has been obtained for the primary quantum yield based on an absorption cross section ratio σ245/σ308=22 for ClOOCl at 245 and 308nm.

Inclusive measurements of inelastic electron and positron scattering from unpolarized hydrogen and deuterium targets

Results of inclusive measurements of inelastic electron and positron scattering from unpolarized protons and deuterons at the HERMES experiment are presented. The structure functions $F_2^p$ and $F_2^d$ are determined using a parameterization of existing data for the longitudinal-to-transverse virtual-photon absorption cross-section ratio. The HERMES results provide data in the ranges $0.006\leq x\leq 0.9$ and 0.1 GeV$^2\leq Q^2\leq$ 20 GeV$^2$, covering the transition region between the perturbative and the non-perturbative regimes of QCD in a so-far largely unexplored kinematic region. They are in agreement with existing world data in the region of overlap. The measured cross sections are used, in combination with data from other experiments, to perform fits to the photon-nucleon cross section using the functional form of the ALLM model. The deuteron-to-proton cross-section ratio is also determined.

Optical limiting response by embedding copper phthalocyanine into polymer host

The multilayer film of PMMA containing mononuclear octakis(mercaptopropylisobutyl-POSS) substituted phthalocyaninato-copper (CuPc) was obtained by spin-coating on quartz substrate. The nonlinear absorption and optical limiting (OL) performance of CuPc have been described using the open-aperture Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The results indicate that CuPc/PMMA composite exhibits a much larger nonlinear absorption coefficient, a lower saturable fluence and a lower absorption cross-section ratio for optical limiting when compared to the same CuPc molecules in solution. No evidence of film fatigue or degradation was observed in the CuPc/PMMA film after numerous scans at varying laser intensity. This material is a good candidate for optical limiting applications.

Emission and absorption cross section of thulium doped silica fibers

A thorough investigation of the emission and absorption spectra of the (3F4,3H6) band in thulium doped silica fibers has been performed. All the basic parameters of thulium in silica have been extracted with the purpose of further analysis in laser and amplifier simulations. The experimental methods used to obtain the scaled cross sections have been carefully selected in order to avoid problems associated with calibrated measurements and knowledge of the radiative lifetime. The values of the absorption cross sections agree well with previously reported values, however the peak emission to peak absorption cross section ratios are found to be significantly below 1. Also confinement factors and thulium concentrations are estimated from the results.

Ratio of absorption cross section for Dirac fermion to that for scalar in the higher-dimensional black hole background

The ratio of the low-energy absorption cross section for Dirac fermion to that for minimally coupled scalar is computed when the spacetimes are various types of the higher-dimensional Reissner–Nordström black holes. It is found that the low-energy absorption cross sections for the Dirac fermion always goes to zero in the extremal limit regardless of the detailed geometry of the spacetime. The physical importance of our results is discussed in the context of the brane-world scenarios and string theories.

Strong Optical Limiting of Soluble Axially Substituted Gallium and Indium Phthalocyanines

Optical limiting in In‐ and Ga‐phthalocyanines exhibits a range of saturation densities and absorption cross‐section ratios. Substitution of the p‐trifluoromethylphenyl group at the central metal in tBu4PcGaCl and tBu4PcInCl reduces the saturation energy density by a factor of >3. Tailorable optical limiting properties are shown in the Figure, which plots the nonlinear absorption coefficient as a function of intensity for the five compounds studied.

Non-linear absorption of alkylsulfonyl metallophthalocyanines

Z-scan experiments have been carried out over two series of novel symmetrically and unsymmetrically substituted alkylsulfonyl metallophthalocyanines. Non-linear absorption coefficients and excited state to ground state absorption cross section ratios (σ ex /σ 0 ) have been assessed for these materials. The results point out that electron-withdrawing substituents have a negative effect on the non-linear absorption behaviour of phthalocyanines.

The effective absorption cross-section of thermal neutrons in a medium containing strongly or weakly absorbing centres

AbstractThe structure of a heterogeneous system influences diffusion of thermal neutrons. The thermal-neutron absorption in grained media is considered in the paper. A simple theory is presented for a two-component medium treated as grains embedded in the matrix or as a system built of two types of grains (of strongly differing absorption cross-sections). A grain parameter is defined as the ratio of the effective macroscopic absorption cross-section of the heterogeneous medium to the absorption cross-section of the corresponding homogeneous medium (consisting of the same components in the same proportions). The grain parameter depends on the ratio of the absorption cross-sections and contributions of the components and on the size of grains. The theoretical approach has been verified in experiments on prepared dedicated models which have kept required geometrical and physical conditions (silver grains distributed regularly in Plexiglas). The effective absorption cross-sections have been measured and compared with the results of calculations. A very good agreement has been observed. In certain cases the differences between the absorption in the heterogeneous and homogeneous media are very significant. A validity of an extension of the theoretical model on natural, two-component, heterogeneous mixtures has been tested experimentally. Aqueous solutions of boric acid have been used as the strongly absorbing component. Fine- and coarse-grained pure silicon has been used as the second component with well-defined thermal-neutron parameters. Small and large grains of diabase have been used as the second natural component. The theoretical predictions have been confirmed in these experiments.

Optical limiting and picosecond relaxation of carbocyanines upper electronic states

Nonlinear absorption, anomalous fluorescence and relaxation of high-lying electronic states in six carbocyanine dyes, including cryptocyanine (DCI), DDI, DTDCI, DTTCI, DOTCI and HDIDCI, in solution and in polymer, were studied by means of picosecond transient absorption spectroscopy and nonlinear transmission experiments. Absorption cross-sections of the S 1→S n transition, and decay rates of the second singlet excited state, S 2, were measured. All dyes showed strong reverse saturable absorption in the 450–600 nm region with large excited to ground state absorption cross-section ratios. For DTDCI this ratio, at 470 nm, was measured to be 350, which is the largest ever reported. All molecules have shown strong optical limiting effect. However, in all molecules except DCI a saturation of the optical limiting process was observed as expected, owing to relatively long, up to 17.5 ps, lifetime of the S 2 state. The S 2 state fluorescence quantum yields were also measured.

Excited state nonlinearity and optical limiting response of cubane-like shaped metal clusters WSe 4(MPPh 3) 3Cl (M=Ag, Cu)

The excited state nonlinearity and optical limiting behaviors of cubane-like shaped clusters [WSe 4(MPPh 3) 3Cl (M=Ag, Cu)] in DMF solution were studied by using a picosecond laser pulses. The excited state absorption capability of clusters [WSe 4(AgPPh 3) 3Cl] is obviously stronger than that of clusters [WSe 4(CuPPh 3) 3Cl]. Influences of skeletal atoms on excited state absorption are significant. The fluence-dependent model was used to describe the optical limiting phenomena, and the ratio of absorption cross-section of the excited state to that of the ground state of clusters [WSe 4(AgPPh 3) 3Cl] is two times greater than that of fullerene.

Transient absorption of symmetrical carbocyanines

Transient absorption in several symmetrical cyanine and carbncyanine dyes is measured by time-resolved spectroscopy with subpicosecond white-light continuum in a wide spectral range (0.35–1 μm). The results are compared with data available in the literature on ultrashort and long-lived transients. The linear shift law observed here for the S 1 S n absorption bands in the wavelength scale allows one to predict the main induced absorption bands for members of several carbocyanine families (vinylogous series) which have not yet been studied. In the case of the shortest methine chains (cyanines and monocarbocyanines) a tew transient absorption bands are assigned to the formation of photoisomers. The absolute values of the excited-state or photoisomer cross sections of polymethine carbocyanines are evaluated by global spectral analysis, from the measured differential optical density spectra. Several cases of large values (higher than 10) of the absorption cross section ratio (excited/ground state) are found at new wavelengths, which allows applications of photo-induced absorption to photonics and laser technologies over a broad spectral range.