Papers by Keyword: Multiple Scattering

Abstract: In this paper, the scattering parameters of aerosol particles are calculated based on Gamma model of atmospheric particle size distribution and the Mie scattering theory for 0.53μm、1.06μm and 10.6μm laser. For the transmission attenuation of the laser in aerosol, the Monte Carlo simulation model is established. The transmittances with propagation distance are calculated for three kinds of wavelength laser in the continental, marine and cumulus aerosols respectively. The results show three kinds of wavelength laser transmission attenuation in cumulus clouds are far stronger than in the continental and marine aerosol. The transmission performance of 10.6μm laser is best in continental aerosol. For marine aerosol, the attenuation to 0.53μm laser is stronger than to 1.06μm and 10.6μm.

Abstract: This work studied the angular distribution of multiple Compton scattering of gamma energy 662 keV, obtained from ¹³⁷Cs source. The gamma rays are incident on carbon scatterer of varying the scattering angles. The phenomenon of multiple Compton scattering has been successfully observed using NaI(Tl) scintillation detector. The energy spectra of the detected photons are observed as a long tail to the single-photon Compton line on the lower side of the full-energy peak in the recorded scattered energy spectrum. The full-energy peak corresponding to singly scattered events is reconstructed analytically and observe that the number of multiply scattered events, having same energy as in the singly scattered distribution.

Abstract: Propagation characteristics of elastic waves in 2D phononic crystal consisting of parallel cylinders embedded periodically in a homogeneous host medium are investigated. The multiple scattering method and the Bloch theorem are used to derive the dispersive equation. The dispersive curves and the band gaps between them are evaluated numerically in the reduced Brillouin zone. The graded interphase between the cylinders and the host are considered. The influences of the graded interphase with different gradient profiles are discussed based on the numerical results.

Abstract: The effective propagation constants of coherent elastic SH wave in composites with random distributed parallel cylindrical nanoholes in host material are studied. The surface elastic theory is used to consider the surface stress effects and to derive the nontraditional boundary condition on the surface of nanoholes. The plane wave expansion method is applied to obtain the scattering waves from the individual cylindrical nanohole. The multiple scattering effects are taken into consideration by the configuration averaging of random distributed scatterers. The effective velocity and attenuation of coherent SH wave are numerically evaluated. The influence of surface stress is discussed based on the numerical results.

Abstract: In this study, we present the characterisation of damage in polymer concrete using coda waves interferometry (CWI). The latter takes into account the multi-scattered acoustic waves, whose travelling distances are considerably longer than the one corresponding to the direct wave (emitter-receiver direct distance). Experimentally, we prove that CWI is not always appropriate to detect damage. Therefore, we propose an original approach through which the interaction CWI with damage is optimised. This is done using nonlinear resonance (NR) method, where bending modes are excited, at the time when acoustic waves are multi-scattered. Experiments show an important increase in the sensitivity to damage with interesting perspectives in terms of damage location and characterisation.

Abstract: Numeric simulation of light passing through the scattering medium by the Monte-Carlo method was carried out. The influence of multiple scattering on the light beam attenuation in an absorbing media was investigated. The additional absorption appearance was shown to be initiated by multiple scattering. The experimental evidence for this absorption is abrupt increasing of beam attenuation at high particle concentrations. The behaviour of the additional absorption was investigated. The results of numeric calculation are in good agreement with experimental results.

Abstract: Continuously tunable random laser basing on rhodamine 6G was achieved. Wavelength tuning was implemented by wedge-shaped sample shift relatively to the pump beam. The physical base of the tuning method is gain band shift caused by reabsorption. We ascertained that two medium thickness ranges of significantly different tune efficiency exist. The lasing characteristics of the laser were investigated depending on active medium and pump beam parameters. The feedback formation mechanisms in the random lasers of different thickness were analyzed.