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Figure 11
2D wavefront retrieval with and without the corrective phase plate, based on single FEL shots and using a π-phase checkerboard grating with 14.1 µm diagonal pitch. (a) Wavefront with phase plate aligned, with scale bar corresponding to 200 µm at the detection plane. (b) Wavefront with phase plate removed. (c) Recovered profile of phase plate, based on subtraction of (b) from (a). The colorbar at the right of (c) is shared among all three phase profiles. The intensity of the beam can also be extracted from the Talbot image (d), which in combination with the retrieved wavefront can be used to obtain profiles of the focus, without (e) and with (f) phase plate correction. From a visual inspection of (e) and (f) it can be seen that the phase plate removes most of the fourth-order spherical aberration, but does not compensate for the astigmatism that likely comes from the monochromator crystals. The scale bar in (f) corresponds to 500 nm and is shared with (e), and the colorbar at right of (f) is shared between (d)–(f).

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