fouriax.critical_distance_um

critical_distance_um(grid, spectrum)

Compute the critical propagation distance separating the ASM and RS regimes.

The boundary is estimated as:

z_crit = N_eff * dx_eff**2 / lambda_min

where N_eff = min(nx, ny), dx_eff = max(dx_um, dy_um), and lambda_min is the shortest wavelength in spectrum. Distances below z_crit favour ASM; distances at or above favour RS.

Parameters:

• grid (Grid) – Spatial sampling grid.

• spectrum (Spectrum) – Wavelength set.

Returns:

Critical distance in micrometers.

Return type:

float