Initial commit: he11lib mode-purity reconstruction library

Full implementation of Laguerre-Gauss modal reconstruction for gyrotron
beam diagnostics, per the approved design spec, plus tests, docs, and
a runnable end-to-end example.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_deconvolution.py

@@ -0,0 +1,67 @@
+import numpy as np
+import pytest
+
+from he11lib.deconvolution import DiffusionDeconvolver
+
+
+def gaussian_bump(n, sigma_px):
+    coords = np.arange(n) - n // 2
+    xx, yy = np.meshgrid(coords, coords)
+    return np.exp(-(xx**2 + yy**2) / (2 * sigma_px**2))
+
+
+def profile_std(image):
+    n = image.shape[0]
+    coords = np.arange(n) - n // 2
+    weights = image[n // 2, :]
+    weights = np.clip(weights, 0, None)
+    mean = np.sum(coords * weights) / np.sum(weights)
+    var = np.sum(weights * (coords - mean) ** 2) / np.sum(weights)
+    return np.sqrt(var)
+
+
+def test_blur_sigma_m_from_diffusivity_and_dwell_time():
+    diffusivity = 1e-6  # m^2/s
+    dwell_time = 0.5  # s
+    deconvolver = DiffusionDeconvolver(thermal_diffusivity=diffusivity, dwell_time=dwell_time)
+
+    expected_sigma = np.sqrt(2 * diffusivity * dwell_time)
+    assert deconvolver.blur_sigma_m() == pytest.approx(expected_sigma)
+
+
+def test_blur_widens_a_sharp_peak():
+    deconvolver = DiffusionDeconvolver(thermal_diffusivity=1e-6, dwell_time=0.5)
+    pixel_scale = 2e-4
+    sharp = gaussian_bump(101, sigma_px=3)
+
+    blurred = deconvolver.blur(sharp, pixel_scale=pixel_scale)
+
+    assert profile_std(blurred) > profile_std(sharp)
+
+
+def test_deconvolve_reduces_error_relative_to_blurred():
+    deconvolver = DiffusionDeconvolver(thermal_diffusivity=1e-6, dwell_time=0.3)
+    pixel_scale = 2e-4
+    sharp = gaussian_bump(101, sigma_px=4)
+
+    blurred = deconvolver.blur(sharp, pixel_scale=pixel_scale)
+    deconvolved = deconvolver.deconvolve(blurred, pixel_scale=pixel_scale)
+
+    error_blurred = np.sum((blurred - sharp) ** 2)
+    error_deconvolved = np.sum((deconvolved - sharp) ** 2)
+    assert error_deconvolved < error_blurred
+
+
+def test_deconvolve_narrows_width_back_toward_original():
+    deconvolver = DiffusionDeconvolver(thermal_diffusivity=1e-6, dwell_time=0.3)
+    pixel_scale = 2e-4
+    sharp = gaussian_bump(101, sigma_px=4)
+
+    blurred = deconvolver.blur(sharp, pixel_scale=pixel_scale)
+    deconvolved = deconvolver.deconvolve(blurred, pixel_scale=pixel_scale)
+
+    std_sharp = profile_std(sharp)
+    std_blurred = profile_std(blurred)
+    std_deconvolved = profile_std(deconvolved)
+
+    assert std_sharp < std_deconvolved < std_blurred