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Figure 3
Physics engine validation against established codes. (a) On-axis undulator flux-density spectrum, normalized to the n = 1 peak and displayed from 2 keV so that harmonics n = 1, 3, 5, 7, 9 and 11 are all visible, at the representative operating point K = 1.87 (gap = 7.14 mm). This work (blue solid) reproduces the SPECTRA calculation (red dashed) for the peak flux density of every displayed harmonic, with the quantitative comparison given in Table 2[link]. (b) Si(111) Darwin width versus photon energy: the engine (blue solid) reproduces the Authier (2001View full citation) analytical width [red dashed; Section S3.8, equation (S9)] over 5–25 keV (Table S10); the green dotted curve (right axis) gives the equivalent relative energy bandwidth ΔE/E (1.32–1.36 × 10−4).

Journal logoJOURNAL OF
SYNCHROTRON
RADIATION
ISSN: 1600-5775
Volume 33| Part 5| September 2026|
https://doi.org/10.1107/S1600577526006788
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