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Absorption Coefficient Alpha

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Clair Baldock – One of the best experts on this subject based on the ideXlab platform.

  • ultrasonic Absorption in polymer gel dosimeters
    Ultrasonics, 2003
    Co-Authors: Melissa L Mather, A F Collings, Nick Bajenov, Andrew K. Whittaker, Clair Baldock

    Abstract:

    Ultrasonic Absorption in polymer gel dosimeters was investigated. An ultrasonic interferometer was used to study the frequency (f) dependence of the Absorption Coefficient (Alpha) in a polyacrylamide gel dosimeter (PAG) in the frequency range 5-20 MHz. The frequency dependence of ultrasonic Absorption deviated from that of an ideal viscous fluid. The presence of relaxation mechanisms was evidenced by the frequency dependence of Alpha/f(2) and the dispersion in ultrasonic velocity. It was concluded that Absorption in polymer gel dosimeters is due to a number of relaxation processes which may include polymer-solvent interactions as well as relaxation due to motion of polymer side groups. The dependence of ultrasonic Absorption on absorbed dose and formulation was also investigated in polymer gel dosimeters as a function of pH and chemical composition. Changes in dosimeter pH and chemical composition resulted in a variation in ultrasonic dose response curves. The observed dependence on pH was considered to be due to pH induced modifications in the radiation yield while changes in chemical composition resulted in differences in polymerisation kinetics. (C) 2003 Elsevier B.V. All rights reserved.

Wenhui Xie – One of the best experts on this subject based on the ideXlab platform.

  • Crystal structure and electronic structure of quaternary semiconductors Cu$_2$ZnTiSe$_4$ and Cu$_2$ZnTiS$_4$ for solar cell absorber
    Journal of Applied Physics, 2012
    Co-Authors: Xiaofeng Wang, Zhenjie Zhao, Sumei Huang, Wenhui Xie

    Abstract:

    We design two new I2-II-IV-VI4 quaternary semiconductors Cu$_2$ZnTiSe$_4$ and Cu$_2$ZnTiS$_4$, and systematically study the crystal and electronic structure by employing first-principles electronic structure calculations. Among the considered crystal structures, it is confirmed that the band gaps of Cu$_2$ZnTiSe$_4$ and Cu$_2$ZnTiS$_4$ originate from the full occupied Cu 3$d$ valence band and unoccupied Ti 3$d$ conducting band, and kesterite structure should be the ground state. Furthermore, our calculations indicate that Cu$_2$ZnTiSe$_4$ and Cu$_2$ZnTiS$_4$ have comparable band gaps with Cu$_2$ZnTSe$_4$ and Cu$_2$ZnTS$_4$, but almost twice larger Absorption Coefficient $\Alpha(\omega)$. Thus, the materials are expected to be candidate materials for solar cell absorber.

C W Rella – One of the best experts on this subject based on the ideXlab platform.

  • Static and dynamic transport of light close to the Anderson localization transition.
    Physical review. E Statistical nonlinear and soft matter physics, 2001
    Co-Authors: J Gómez Rivas, R Sprik, A Lagendijk, L D Noordam, C W Rella

    Abstract:

    Anderson localization of light refers to an inhibition of wave transport in scattering media due to the interference of multiple scattered waves. We present wavelength dependent midinfrared optical transport measurements in slabs of randomly packed germanium (Ge) micron-sized particles, using a free electron laser as a tunable source of pulsed radiation. Because of their high refractive index and low Absorption, Ge and similar semiconductors are excellent systems to study Anderson localization of light. To characterize the samples fully, we have employed several complementary optical techniques: total diffuse transmission, total diffuse reflection, coherent transmission, and time-resolved speckle interferometry. In this way we obtained the scattering (l(s)) and transport (l) mean free paths, the Absorption Coefficient (Alpha), the diffusion constant (D), and the energy transport velocity (v(e)). These measurements have been made as a function of midinfrared wavelength, so that the scattering cross section and Absorption Coefficients can be varied in the same samples. We found that the Ge samples are close (kl(s) approximately 3) to the localization transition, but still above it. Our measurements of l(s) and l suggest that l is renormalized due to interference at the proximity of the localization transition. We also found that the diffusion constant is significantly reduced in samples thinner than approximately 7l.