Martino Ferrari
03b63ba03a
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>
85 lines
3.0 KiB
Python
85 lines
3.0 KiB
Python
import numpy as np
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import pytest
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from he11lib.modes import LGBasis
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from he11lib.phase_retrieval import PhaseRetriever, propagate_angular_spectrum
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from he11lib.synthetic import SyntheticBeamGenerator
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W0 = 5e-3
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Z0 = 0.5
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WAVELENGTH = 1.76e-3
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PIXEL_SCALE = 3e-4
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IMAGE_SHAPE = (121, 121)
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def make_basis():
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return LGBasis(w0=W0, z0=Z0, wavelength=WAVELENGTH)
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def make_grid():
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coords = (np.arange(IMAGE_SHAPE[0]) - IMAGE_SHAPE[0] // 2) * PIXEL_SCALE
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x, y = np.meshgrid(coords, coords)
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return x, y
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def test_propagate_round_trip_recovers_original_field():
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basis = make_basis()
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x, y = make_grid()
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field = basis.field(x, y, Z0, p=0, l=0)
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forward = propagate_angular_spectrum(field, PIXEL_SCALE, dz=0.05, wavelength=WAVELENGTH)
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back = propagate_angular_spectrum(forward, PIXEL_SCALE, dz=-0.05, wavelength=WAVELENGTH)
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np.testing.assert_allclose(back, field, atol=1e-3 * np.max(np.abs(field)))
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def test_propagate_matches_lgbasis_analytic_evolution():
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basis = make_basis()
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x, y = make_grid()
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field_at_waist = basis.field(x, y, Z0, p=0, l=0)
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dz = 0.05
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propagated = propagate_angular_spectrum(field_at_waist, PIXEL_SCALE, dz=dz, wavelength=WAVELENGTH)
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analytic = basis.field(x, y, Z0 + dz, p=0, l=0)
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# compare intensity profiles (phase reference/global constant may differ)
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np.testing.assert_allclose(
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np.abs(propagated) ** 2, np.abs(analytic) ** 2, atol=1e-2 * np.max(np.abs(analytic) ** 2)
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)
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def test_retrieve_recovers_pure_mode_purity():
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# Keep z distances close to the waist so the (widening) beam stays well
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# within the frame -- otherwise FFT wraparound/clipping at the edges
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# degrades angular-spectrum propagation accuracy.
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basis = make_basis()
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gen = SyntheticBeamGenerator(basis=basis, image_shape=IMAGE_SHAPE, pixel_scale=PIXEL_SCALE)
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z_list = [0.47, 0.5, 0.53]
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planes = gen.generate(coefficients={(0, 0): 1.0 + 0j}, z_list=z_list, noise_std=1e-5, seed=0)
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retriever = PhaseRetriever(wavelength=WAVELENGTH)
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result = retriever.retrieve(planes, viewing_angle_deg=0.0, max_iterations=100)
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coeffs = basis.project(
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result.field, result.x, result.y, PIXEL_SCALE, result.z, modes=[(0, 0), (1, 0), (0, 1)]
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)
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total_power = sum(abs(c) ** 2 for c in coeffs.values())
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purity_00 = abs(coeffs[(0, 0)]) ** 2 / total_power
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assert purity_00 > 0.9
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def test_retrieve_estimates_beam_center():
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basis = make_basis()
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gen = SyntheticBeamGenerator(basis=basis, image_shape=IMAGE_SHAPE, pixel_scale=PIXEL_SCALE)
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z_list = [0.47, 0.5, 0.53]
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true_center = (15 * PIXEL_SCALE, -8 * PIXEL_SCALE)
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planes = gen.generate(
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coefficients={(0, 0): 1.0 + 0j}, z_list=z_list, center=true_center, noise_std=1e-5, seed=1
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)
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retriever = PhaseRetriever(wavelength=WAVELENGTH)
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result = retriever.retrieve(planes, viewing_angle_deg=0.0, max_iterations=100)
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assert result.center[0] == pytest.approx(true_center[0], abs=3 * PIXEL_SCALE)
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assert result.center[1] == pytest.approx(true_center[1], abs=3 * PIXEL_SCALE)
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