# Stopped 200 nm SiN Fourier atom-hole campaign

This page freezes the 200 nm thickness experiment at the checkpoint selected
for replacement by the finite SiO2-clad stack. It remains an exploratory,
continuous-density result; it did not run through binarization and is not
presented as a finished device.

## Executed configuration and outcome

| Quantity | Value |
|---|---:|
| Material stack | 200 nm Si3N4 slab in infinite SiO2 |
| Atom | z-oriented, 780.24 nm |
| Immutable opening | 1.0 µm-diameter through-slab air hole |
| Trainable region | 9.6 µm-diameter extruded 2-D mask |
| Grid / symmetry | 25 nm / x-y-z (8× reduced solve) |
| Active controls | 40,000 real Fourier coefficients |
| Accepted updates | 69 |
| Initial / final / best LDOS | 0.517264 / **0.595742** / **0.595742** |
| LDOS gain | **15.17%** |
| Final grayness | 0.6140 |
| Final field / energy fitted Q | 34.03 / 65.17, rejected |

The largest apparent conservative Q in three pulsed audits was 174.39, but it
failed the field/energy residual and window-stability gates. The optimizer
therefore never entered shifted-pole mode. This is the intended fail-closed
behavior, not evidence of a Q=174 cavity.

## Geometry at the stopping point

```{figure} ../_static/generated/fourier_atom_hole_sin200_final_geometry.png
:alt: Cold start and stopped 200 nm geometry with complete xz material sections

The initial spectral seed, final continuous mask, and literal 200 nm material
cross-section at update 69.
```

## Optimization and pole-audit history

```{figure} ../_static/generated/fourier_atom_hole_sin200_final_progress.png
:alt: LDOS, continuation, grayness, gradient, and pole audits of the 200 nm campaign

LDOS improved monotonically over the short run. Untrusted Q fits are shown as
diagnostics and never used to recenter the objective.
```

## Spatial spectrum and electric field

```{figure} ../_static/generated/fourier_atom_hole_sin200_final_spectrum.png
:alt: Fourier controls at the stopped 200 nm checkpoint
```

```{figure} ../_static/generated/fourier_atom_hole_sin200_final_field.png
:alt: Ez field over the xy plane and complete xz domain at the stopped checkpoint

The complete xz panel includes the PML entrances. A stronger validation doubled
the physical z interior from 1.8 to 3.6 µm at update 67; LDOS changed only
-0.000160% (0.59500849 to 0.59500754). The visible upward and downward field is
therefore outgoing radiation rather than a measurable finite-z artifact at this
checkpoint.
```

The resumable artifact remains at
`benchmarks/artifacts/invdes_fourier_atom_hole_ldos_sin200_isotropic_v1.npz`.