fix[adjoint]: fix diffraction data adjoint source creation

Author: Gregory Roberts

CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 - Validate mode solver object for large number of grid points on the modal plane.
 
+### Fixed
+- Fixed missing amplitude factor and handling of negative normal direction case when making adjoint sources from `DiffractionMonitor`.
+
 ## [2.9.0] - 2025-08-04
 
 ### Added

tests/test_components/test_autograd_mode_polyslab_numerical.py

@@ -457,7 +457,7 @@ def eval_fn(sim_data):
     fd_mag = np.linalg.norm(fd_grad)
     adj_mag = np.linalg.norm(pattern_dot_adj_gradient)
     percentage_error = 100.0 * np.mean(
-        (fd_grad - pattern_dot_adj_gradient) / (fd_grad + np.finfo(np.float64).eps)
+        np.abs(fd_grad - pattern_dot_adj_gradient) / (np.abs(fd_grad) + np.finfo(np.float64).eps)
     )
 
     print("\n" * 3)

tests/test_components/test_autograd_numerical.py

@@ -333,7 +333,7 @@ def test_finite_difference_field_data(field_data_test_parameters, rng, tmp_path,
     fd_mag = np.linalg.norm(fd_grad)
     adj_mag = np.linalg.norm(pattern_dot_adj_gradient)
     percentage_error = 100.0 * np.mean(
-        (fd_grad - pattern_dot_adj_gradient) / (fd_grad + np.finfo(np.float64).eps)
+        np.abs(fd_grad - pattern_dot_adj_gradient) / (np.abs(fd_grad) + np.finfo(np.float64).eps)
     )
 
     print("\n" * 3)