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| Both sides previous revision Previous revision Next revision | Previous revision Next revision Both sides next revision | ||
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docs:become [2020/04/22 15:27] pklapetek |
docs:become [2020/04/22 21:34] pklapetek |
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| //periodic NFFF// in the next text. | //periodic NFFF// in the next text. | ||
| In most of the graphs here we show complete diffraction pattern. | In most of the graphs here we show complete diffraction pattern. | ||
| - | However, if we are interested in the maximum in some diffraction order direction, it is much simpler and it seems that this is the preferably used approach - we calculate the far field value only at the diffraction order maximum. Luckily enough, this value is dependent on the aperture only, which constructs the envelope for the diffraction pattern, so in this case one could work only with a single aperture. However, to construct the diffraction pattern is a good way how to debug the problem. | + | However, if we are interested in the maximum in some diffraction order direction, it is much simpler and it seems that this is the preferably used approach - we calculate the far field value only at the diffraction order maximum. Luckily enough, this value is dependent on the aperture only, which constructs the envelope for the diffraction pattern, so in this case one could work only with a single aperture. However, to construct the diffraction pattern is a good way how to debug the problem. The schematics of |
| + | the calculations is here: | ||
| + | |||
| + | {{:docs:schematics.png?600|}} | ||
| A comparison of the different evaluation methods is shown below, also showing the first | A comparison of the different evaluation methods is shown below, also showing the first | ||
| Line 28: | Line 32: | ||
| periodic calculation (based on a single motive) where the far field is evaluated from three | periodic calculation (based on a single motive) where the far field is evaluated from three | ||
| and nine virtual repetitions are then compared to the case where the calculation is not periodic | and nine virtual repetitions are then compared to the case where the calculation is not periodic | ||
| - | and three apertures are physically existing in the computational domain. The schematics of | + | and three apertures are physically existing in the computational domain. |
| - | the calculations is here: | + | |
| - | + | ||
| - | {{:docs:schematics.png?600|}} | + | |
| An important message is that | An important message is that | ||
| Line 59: | Line 60: | ||
| The transition from transition geometry to reflection geometry was done first with perfect electric conductor as a grating material. The same motive as in the Become grating is used and also | The transition from transition geometry to reflection geometry was done first with perfect electric conductor as a grating material. The same motive as in the Become grating is used and also | ||
| the same voxel spacing (5 nm), it is only from a different materials for calculation speed and simplicity. All the computational details were same as in the previous example. | the same voxel spacing (5 nm), it is only from a different materials for calculation speed and simplicity. All the computational details were same as in the previous example. | ||
| + | To get the data normalization to the incident wave intensity we used perfect electric conductor plane only (no grating motives) and evaluated the electric field intensity in | ||
| + | the far field point corresponding to surface normal direction. | ||
| Here, we don't have any analytical result to which | Here, we don't have any analytical result to which | ||
| Line 82: | Line 84: | ||
| The **Become benchmark grating** was setup the same way as the above test example. | The **Become benchmark grating** was setup the same way as the above test example. | ||
| - | The grating was now formed by silver, using the PLRC metal handling approach. | + | The grating was now formed by silver, using the PLRC metal handling approach. |
| - | + | All the other parameters we kept from the previous case. Normalization was again | |
| - | 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). | + | done via reflection from a perfect electric conductor surface. |
| - | 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. | + | |
| - | + | ||
| - | {{: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 | ||
| - | the far field point corresponding to surface normal direction was evaluated and used as a reference | ||
| - | in all the other calculations. | ||
| The image below shows the normalized angular dependence of the diffraction from the (finite size) grating. | The image below shows the normalized angular dependence of the diffraction from the (finite size) grating. | ||
| - | {{:docs:become_grating_2d_normalised.png?600|}} | + | {{:docs:result_twomethods.png?600|}} |
| 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). | 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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| + | ===== Summary ===== | ||
| + | The sensitivity of 2D calculations results on the settings (computational domain size, time step, near-to-far field transformation, et.c) is in the order of few percent, the dominant effect of this uncertainty is the near-to-far field transformation. This does not affect the cases when these conditions are kept same in a series of calculations (so relative changes can be calculated with much higher accuracy), however it certainly affects the absolute values, e.g. when comparing a single calculation to completely different calculation or experimental data. | ||
| ===== TODO ===== | ===== TODO ===== | ||
docs/become.txt · Last modified: 2020/04/24 12:27 by pklapetek
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