> For the complete documentation index, see [llms.txt](https://simplemetalens.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://simplemetalens.gitbook.io/docs/smd-pro/tutorial/lens-characterization/near-field-analysis.md).
# Near-Field Analysis
A lens scales down the distance over which diffraction patterns develop from an aperture; near-field patterns before the focus and the far-field pattern at the focus. Fig. 1 shows the intensity distribution at a given position before the focus and at the focus for the lens introduced in [Tutorial](/docs/smd-pro/tutorial/basic-workflow/1.-build-a-metalens.md). The substrate thickness 50 µm and a square aperture were used for the [simulation](/docs/smd-pro/tutorial/basic-workflow/2.-simulate/2.1.-focusing.md). Fig. 2 shows simulation parameters for the incident beam, simulation ranges, and defocus.
Fig. 1. Intensity plots before and at focus. Focal distance is 50 µm.
Fig. 2. Simulation settings for defocus -31 µm.
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