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Capabilities of the discrete dipole approximation for large particle ...

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for large particle systems. Maxim A. Yurkin1,2. 1 Voevodsky Institute of Chemical Kinetics and Combustion, Novosibirsk, Russia. 2 Novosibirsk State University, ...
International Symposium on Electromagnetic Theory (EMTS 2016), Espoo, Finland, 16.08.2016

Capabilities of the discrete dipole approximation for large particle systems Maxim A. Yurkin1,2

Voevodsky Institute of Chemical Kinetics and Combustion, Novosibirsk, Russia 2 Novosibirsk State University, Novosibirsk, Russia 1

Plan 

DDA basics



Computational issues    

Fast-multipole method Multi-grid DDA Number of iterations Orientation averaging



Application examples



Multiple scattering and physical preconditioner



Conclusion

2

Discrete dipole approximation 









Solves the integral Maxwell equation for the electric field in the frequency domain using the volume discretization. Cubical subvolumes (dipoles), have typical size d ~ λ/10. Polarizability of each dipole is determined by local (complex) refractive index. Dipoles interact with each other and the incident light ⇒ system of linear equations ⇒ solved to determine dipole polarizations. Any measurable quantity is determined from dipole polarizations.

Purcell & Pennypacker, Astrophys. J. 186, 705-714 (1973). Draine & Flatau, JOSA A 11, 1491-1499 (1994). Yurkin & Hoekstra, J. Quant. Spectrosc. Radiat. Transfer 106, 558-589 (2007).

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Master equation E(r ) = Einc (r ) +

3 d ∫ r ′G (r − r′) χ (r′)E(r′) + M(V0 , r) − L (∂V0 , r) χ (r)E(r)

V \V0

exp(ikR)  2  Rˆ Rˆ  1 − ikR  Rˆ Rˆ   I − 3 2  G (R ) = k  I − 2  − 2 R R  R  R   

χ (r ) = (m 2 (r ) − 1) 4π

Volume discretization

αi−1Pi − ∑ G ij P j = Einc i j ≠i

Pi = Vi χ i Ei

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Measurable quantities (scattering) exp(ikr ) E (r ) = F (n) − ikr F(n) = −ik 3 ( I − nˆ nˆ )∑ Pi exp(−ikri ⋅ n) sca

Distribution of EM field in space

i

(

* Cext = 4πk ∑ Im Pi ⋅ Einc i

)

i

Cabs = 4πk ∑ Im(Pi ⋅ E*i )

Integral quantities

i

Csca

1 2 = 2 ∫ dΩ F (n) = Cext − Cabs k

DDA is a “numerically exact” method! Yurkin et al., JOSA A 23, 2578–2591 (2006).

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Computational issues 

System of 3Nd linear equations (up to 109)



Matrix of the system is dense.







Regular cubical grid, G (r, r′) = G (r − r′) ⇒ matrix is multilevel block-Toeplitz Memory requirements – 𝒪(N), matrix-vector product ⇒ FFT-based convolution – 𝒪(NlogN)

Iterative solvers usually converge in Niter

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