Light scattering by porous dust particles in the discrete-dipole approximation

1994 ◽  
Vol 425 ◽  
pp. 653 ◽  
Author(s):  
K. Lumme ◽  
J. Rahola
Keyword(s):  
Light Scattering ◽  
Dipole Approximation ◽  
Discrete Dipole Approximation ◽  
Dust Particles

Large Scale Simulations of Elastic Light Scattering by a Fast Discrete Dipole Approximation

1998 ◽  
Vol 09 (01) ◽  
pp. 87-102 ◽  
Author(s):  
A. G. Hoekstra ◽  
M. D. Grimminck ◽  
P. M. A. Sloot
Keyword(s):  
Light Scattering ◽  
Blood Cells ◽  
Large Scale ◽  
Incident Light ◽  
Spherical Inclusion ◽  
White Blood Cells ◽  
Dipole Approximation ◽  
Discrete Dipole Approximation ◽  
Dust Particles ◽  
Elastic Light Scattering

Simulation of Elastic Light Scattering from arbitrary shaped particles in the resonance region (i.e., with a dimension of several wavelengths of the incident light) is a long standing challenge. By employing the combination of a simulation kernel with low computational complexity, implemented on powerful High Performance Computing systems, we are now able to push the limits of simulation of scattering of visible light towards particles with dimensions up to 10 micrometers. This allows for the first time the simulation of realistic and highly relevant light scattering experiments, such as scattering from human red — or white blood cells, or scattering from large soot — or dust particles. We use the Discrete Dipole Approximation to simulate the light scattering process. In this paper we report on a parallel Fast Discrete Dipole Approximation, and we will show the performance of the resulting code, running under PVM on a 32-node Parsytec CC. Furthermore, as an example we present results of a simulation of scattering from human white blood cells. In a first approximation the Lymphocyte is modeled as a sphere with a spherical inclusion. We investigate the influence of the position of the inner sphere, modeling the nucleus of a Lymphocyte, on the light scattering signals.

scholarly journals Experimental verification of agglomeration effects in infrared spectra on micron-sized particles

2018 ◽  
Vol 619 ◽  
pp. A110 ◽  
Author(s):  
Akemi Tamanai ◽  
Jochen Vogt ◽  
Christian Huck ◽  
Uwe Mick ◽  
Sören Zimmermann ◽  
...  
Keyword(s):  
Light Scattering ◽  
Theoretical Calculations ◽  
Dust Emission ◽  
Emission Spectra ◽  
Dipole Approximation ◽  
Dust Particles ◽  
Vibration Band ◽  
Extinction Spectra ◽  
Theoretical Approaches ◽  
Stretching Vibration

Context. Detailed analysis of observed infrared (IR) dust emission spectra is often performed in order to derive information about mineralogy, particle size, and temperature of the dust. However, the IR bands are also influenced by agglomeration of the dust particles. Light scattering theory simulating agglomeration and growth effects is especially challenged by the consideration of highly absorbing particles. Aims. To clarify the influence of agglomeration on the diagnostic phonon bands of amorphous SiO2 particles, we experimentally measure the extinction spectra of systematically arranged particle configurations and compare the measured spectra with the spectra obtained from different theoretical approaches. Methods. We construct artificial particle agglomerates by means of the dedicated robotic manipulation (DRM) technique. IR microspectroscopic extinction measurements of these arranged particles are performed at the French National Synchrotron Facility, SOLEIL, in the mid-IR region considering polarization effects. The theoretical approaches applied are the discrete dipole approximation (DDA) as well as T-matrix and finite-difference time-domain methods. Results. In both the experimental spectra and the theoretical calculations, we find that the Si–O stretching vibration band at about 9 μm is clearly broadened on the long-wavelength side by the agglomeration of particles. This is mainly caused by the radiation components, which are polarized in directions in which the agglomerate is extended, while the extinction band profile of the component polarized perpendicular to the long axis of an elongated agglomerate is close to the spectrum of the single sphere. All of the theoretical simulations predict these effects in qualitatively good agreement. Conclusions. Our comparative study of the experimentally measured and theoretically calculated IR extinction spectra of well-defined agglomerate structures makes obvious how the various particle arrangements in small clusters might contribute to average spectra of dust. Therefore the study might help to improve the precision of light scattering calculations as well as their specific applicability.

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