Local degree of optical chirality

05 December, 2023

Objective

This example illustrates on a very simple case the calculation of the local degree of optical chirality for a dimer of spheres. The structure consists of two gold spheres with radius 10nm and gap 5nm in water, the incident field is linear with angle \(\pi/4\) and \(3\pi/4\) and \(\overline{\mathscr{C}}\) is calculated at the resonance wavelength of the structure and all other parameters are kept to their default values.

This simulation uses the following input file

ModeAndScheme 1 0
MultipoleCutoff 8
Wavelength 540
Medium 1.7689 # water

OutputFormat HDF5 ldoc
Incidence file incidence 1  # linear polarisation, 45 & 135
SpacePoints -15 15 90 -25 25 150 0 0 0
MapQuantity C

Scatterers 2
Au 0 12.5 0 10
Au 0 -12.5 0 10

and incidence file

2
0.7853982 0 0 0.5
2.356194  0 0 0.5

LDOC maps at fixed incidence

        group            name       otype dclass       dim
0           /      Near-Field   H5I_GROUP                 
1 /Near-Field      Gridpoints H5I_DATASET  FLOAT 13741 x 3
2 /Near-Field      Incidences H5I_DATASET  FLOAT     2 x 4
3 /Near-Field     Wavelengths H5I_DATASET  FLOAT         1
4 /Near-Field normalised_ldoc H5I_DATASET  FLOAT 13741 x 7

 num [1:13741, 1:7] 540 540 540 540 540 540 540 540 540 540 ...

Orientation-averaged near-field and LDOC maps

TERMS can also compute orientation-averaged near-field quantities, with the Keyword MapOaQuantity. This structure is not particularly good at enhancing the local degree of chirality, but we use it as a simple example to illustrate the results of this calculation. The following map shows the orientation averaged LDOC for L and R circular polarisations.

        group          name       otype dclass       dim
0           /    Near-Field   H5I_GROUP                 
1 /Near-Field    Gridpoints H5I_DATASET  FLOAT 13741 x 3
2 /Near-Field    Incidences H5I_DATASET  FLOAT     1 x 4
3 /Near-Field   Wavelengths H5I_DATASET  FLOAT         1
4 /Near-Field mapOaQuantity H5I_DATASET  FLOAT 13741 x 7
5 /Near-Field         map_E H5I_DATASET  FLOAT 13741 x 7

  wavelength   x         y z        E         R        L
1        540 -15 -25.00000 0 1.362272 -1.025050 1.025050
2        540 -15 -24.66667 0 1.383590 -1.025919 1.025919
3        540 -15 -24.33333 0 1.405998 -1.026835 1.026835
4        540 -15 -24.00000 0 1.429517 -1.027800 1.027800
5        540 -15 -23.66667 0 1.454160 -1.028815 1.028815
6        540 -15 -23.33333 0 1.479935 -1.029881 1.029881

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Last run: 05 December, 2023