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Invited Article: Coherent imaging using seeded free-electron laser pulses with variable polarization: First results and research opportunities
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Image of FIG. 1.
FIG. 1.

(a) Beamline layout. (b) DiProI end-station connected to the double chamber hosting the K-B focusing system. (c) Optical microscope image of an ablated crater, created in a PMMA sample by the focused beam. (d) Indirect multi-layer mirror-CCD detection system. (e) X-CAM direct detection system.

Image of FIG. 2.
FIG. 2.

(Top) Interference fringes for Young's double pinhole experiments with separation (a) 2 m and (b) 20 m. (Bottom) Line profiles of interference fringes (blue dots) and fit of experimental data with Eq. (1) for separation (c) 2 m and (d) 20 m.

Image of FIG. 3.
FIG. 3.

Measured degree of transverse coherence at 32.5 nm as a function of the separation between the two pinholes for focused (25 m) beam (blue circles) and unfocused beam before the K-B mirror (red squares). For the sake of comparison, the axis shows the normalized distance separation, dividing by the beam dimension . Dashed lines show the fit of the experimental data with the Gaussian Schell model considering the contribution of a single mode (black) or three modes (green).

Image of FIG. 4.
FIG. 4.

(a) and (b) SEM image of the samples; profiles taken along the dashed yellow lines are shown in Figures 5(a) and 5(b) . (c) and (d) Single-shot diffraction pattern with 32.5 nm FEL pulse. (e) and (f) Holographic reconstruction of the objects (dashed yellow squares highlight their positions), with one enlarged hologram in the inset. (g) and (h) Phase retrieval reconstruction.

Image of FIG. 5.
FIG. 5.

(a) and (b) Profiles taken along the dashed yellow lines in the SEM images of Figures 4(a) and 4(b) and in the corresponding CDI reconstructed images (Figures 4(g) and 4(h) ). (c) and (d) PRTF obtained averaging the Fourier amplitude of 10 independent reconstructions with different random phases as starting guess; the dashed lines highlight where the PRTF drop below 1/.

Image of FIG. 6.
FIG. 6.

(a) Atomic scattering form factor of cobalt taken from Ref. : dots highlight the measurement wavelengths in (b)–(f) around the resonance at the Co -edge at 20.8 nm. (b)–(f) Scattering patterns of a Co/Pt multilayer sample at 23.5 nm, 21.0 nm, 20.8 nm, 20.6 nm, and 20.4 nm. (g) Radial average of (b)–(f) showing a maximum of magnetically scattered photons at the Co absorption edge (20.8 nm).

Image of FIG. 7.
FIG. 7.

(a)–(f) Magnetic scattering patterns taken with different fluences: (a) 100 pulses with average energy 0.15 J; (b) 50 pulses with average energy 0.6 J; (c) 50 pulses with average energy 1 J; (d) single-shot pulse of 4.3 J; (e) successive single-shot pulse of 4 J; and (f) integrative image of 5 successive pulses of ∼3.5 J. (g) Plots of the scattering profiles obtained by azimuthally averaging intensities of images (a)–(f). (h) Dependence of the peak position of the scattering pattern on the average pulse energy.

Image of FIG. 8.
FIG. 8.

(a) Experimental setup. Scanning electron microscopy image of the 5-references holography mask: the sample aperture is 2.5 m and the references 100 nm. A single-shot spectro-hologram is acquired on a CCD camera located at 48 mm downstream. (b) Reconstructed hologram of the magnetic structure using the diffraction pattern in (a): dark and bright regions are domains with opposite out-of-plane magnetization directions. (c) CDI reconstruction of the magnetic structure, using image (b) as starting guess in RAAR phase retrieving algorithm. (d) Intensity profile along the yellow line in (c).


Generic image for table
Table I.

FERMI FEL-1 key parameters relevant to the present experiments.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Invited Article: Coherent imaging using seeded free-electron laser pulses with variable polarization: First results and research opportunities