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docs:become [2020/03/28 22:24] pklapetek |
docs:become [2020/04/02 11:21] pklapetek [2D calculation] |
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| The grating has period of w1 = 1000 nm and is formed by protrusion of width w2 = 500 nm and height h = 60 nm. The refractive index for the wavelength of λ0 = 619.9 nm is (0.131+3.88i). | The grating has period of w1 = 1000 nm and is formed by protrusion of width w2 = 500 nm and height h = 60 nm. The refractive index for the wavelength of λ0 = 619.9 nm is (0.131+3.88i). | ||
| - | Illumination is from normal direction, P-polarized, Goal is to investigate convergence of quantity of interest, which is the first order maximum s+1. | + | Illumination is from normal direction, P-polarized, Goal is to investigate convergence of quantity of interest, which is the first order maximum s+1. This should be roughly 0.186. |
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| handling was tested via comparing the spectral reflectivity to the database data. | handling was tested via comparing the spectral reflectivity to the database data. | ||
| - | The Become benchmark grating was setup with voxel spacing of 5 nm in every direction. The total computational domain size was 240x100 voxels. The grating was formed by silver, using the PLRC metal handling approach. Periodic boundary conditions were used to introduce the grating periodicity. Total/scattered field approach was used to inject the plane wave normally to the surface. Near-to-far field calculation domain was set up to be outside of the plane wave source region, so only reflected and scattered electric field was propagated to the far-field. Time domain far field calculation was used. Far field data were calculated for wide range of angles for debugging purposes (i.e. not only for the directions of the particular diffraction orders). | + | The Become benchmark grating was setup with voxel spacing of 5 nm in every direction. The total computational domain size was 240x100 voxels. The grating was formed by silver, using the PLRC metal handling approach. Periodic boundary conditions were used to introduce the grating periodicity. Total/scattered field approach was used to inject the plane wave normally to the surface. TE mode calculation was used for this 2D case, which should be the p-polarisation case as requested. Near-to-far field calculation domain was set up to be outside of the plane wave source region, so only reflected and scattered electric field was propagated to the far-field. Time domain far field calculation was used. Far field data were calculated for wide range of angles for debugging purposes (i.e. not only for the directions of the particular diffraction orders). |
| + | The model setup and a calculation snapshot of the periodic area are shown in the following figure. | ||
| + | The far field was evaluated from a fixed number of repetitions of the near-field values, the presented results therefore represent scattering by a finite size grating. The far field value in the direction of the maxima is however not affected by size of grating (number of repetitions), only its sharpness is affected. | ||
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| + | {{:docs:model.png?600|}} | ||
| To get the data normalization to the incident wave intensity we used a similar model where the grating was replaced by a perfect electric conductor plane. The electric field intensity in | To get the data normalization to the incident wave intensity we used a similar model where the grating was replaced by a perfect electric conductor plane. The electric field intensity in | ||
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| in all the other calculations. | in all the other calculations. | ||
| - | The image below shows the normalized angular dependence of the diffraction from the grating. | + | The image below shows the normalized angular dependence of the diffraction from the (finite size) grating. |
| + | {{:docs:become_grating_2d_normalised.png?600|}} | ||
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| + | When inspected in detail, it can be seen that there is a slight asymmetry in the result which needs to be analyzed, probably due to wrong placement of far-field points. The average intensity of the s+1 and s-1 diffraction orders is 0.178 of the incident intensity for the default silver model (not the Become one). | ||
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| + | List of different settings and results: | ||
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| + | * metal setting: 6 1.03583 0 1.37537e+16 1.25733e+14 2.1735 -0.504659 7.60514e+15 4.28131e+15 0.554478 -1.48944 6.13809e+15 6.62262e+14 leads to: 0.172 * | ||
| ===== 3D calculation ===== | ===== 3D calculation ===== | ||
| The 3D calculation was a simple extension of the 2D case, so the voxel spacing was again 5 nm in every direction and computational domain size was 240x240x100 voxels. | The 3D calculation was a simple extension of the 2D case, so the voxel spacing was again 5 nm in every direction and computational domain size was 240x240x100 voxels. | ||
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| The aspects that need further investigation or tuning: | The aspects that need further investigation or tuning: | ||
| - | * polarisation correctness | + | * far-field calculation postprocessing speedup, now very slow, printing many debugging data. |
| - | * far-field calculation postprocessing speedup | + | * cross-check metal refractive index (now relying on pre-fitted database data, which is wrong) |
| - | * correct metal refractive index (now relying on pre-fitted database data) | + | * there is still slight asymmetry |
| - | * correct placement of far field points (slight asymmetry observed) | + | * evaluate the voxel size vs. speed vs. accuracy for the benchmark. |
docs/become.txt · Last modified: 2020/04/24 12:27 by pklapetek
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