DiProI 2015

DiProI beamline at FERMI@Elettra The lensless Coherent Diffraction Imaging (CDI) technique has been developed significantly and is gaining time resolved potentials thanks to the advent of coherent and ultrashort pulses delivered by the X-ray free electron lasers (FEL). The shot-to-shot temporal and energy stability of the seeded-FEL pulses at Fermi@Elettra has opened extraordinary opportunities for CDI and in particular for Resonant Coherent Diffraction Imaging (R-CDI  ),   overcoming some of the limitations imposed by the partial longitudinal coherence of the SASE-FELs.In addition, the multiple (linear and circular) polarization of Fermi-FEL pulses is an added value to explore specific contrast mechanisms, relevant to the spin and orbital sensitive electronic transitions.

Ptychography with OAM beams Light beams possessing orbital angular momentum (OAM) are characterized by distinctive amplitude and phase structures. We were able to investigate how such a peculiar illumination, combined with optical aberrations, enhances the quality of ptychographic images obtained at the FERMI FEL source.      Pancaldi et al., Optica, Vol. 11 - 3, pp. 403-411 (2023).   Read More Single shot 3D imaging The 3D map of an isolated object is obtained impinging simultaneously with two “twin” EUV FEL pulses from different directions. This new technique was designed on DiProI taking advantage of novel data analysis algorithms developed in collaboration with the Scientific Computing Team (SciComp).    Fainozzi et al., Optica, Vol. 10 - 8, pp. 1053-1058 (2023).   Read More Magnetic and light vortices Magnetic helicoidal dichroism is observed when an extreme ultraviolet vortex beam, carrying Orbital Angular Momentum (OAM), interacts with a magnetic vortex. Classical electromagnetic simulations predict this dichroism based on the interference of light OAM modes, populated after the interaction with the magnetic topology. Fanciulli et al., Physical Review Letters, Vol. 128 - 7, p. 077401 (2022).   Read More Evolution of chiral magnetic domain walls The chirality of Néel magnetic domain walls can be measured by x-ray circular dichroism in resonant magnetic scattering. Their ultrafast evolution is explained as an increase of the walls width and a reduction of the magnetization, due to a spin current of hot electrons passing from the domain through the domain walls. Léveillé et al., Nature Communications, Vol. 13 - 1, pp. 1412 (2022).   Read More Faster chiral magnetic order recovery Studying the ultafast dynamics of chiral spin structures (Skyrmions) stabilized by Dzyaloshinskii-Moriya interaction (DMI) after optical excitation, the observed recovery of the chiral magnetic order is faster than the average collinear domain magnetization. Kerber et al., Nature Communications, Vol. 11 - 1, pp. 6304 (2020).   Read More Diffractive fluence mapping The FEL fluence spatial distribution on the target can be mapped by drilling customized diffraction gratings on the sample membrane, providing real space imaging of the beam spot at the sample plane. This can be used to properly align the sample on the beam focus and to recover the single shot intensity profile of the pulse used in the experiment. Schneider et al., Nature Communications, Vol. 9 - 1, pp. 214 (2018).   Read More Multi-color magnetic imaging Nanoscale magnetic domain networks in Co/Pt heterostructure are spatially resolved through coherent imaging with Fourier-transform holography. Irradiating the holographic sample at the same time with two harmonics of the FEL seed, at resonance with O and Pt respectively, two element specific images are retrieved at the same time. Willems et al., Structural Dynamics, 4, 014301 (2017).   Read More Mini-TIMER: four wave mixing with FEL transient gratings Extreme ultraviolet four wave mixing have been demonstrated at the DiProI beamline producing a transient grating with 70 fs FEL pulses, split into two halves and recombined on the sample with a known delay, and probing it with a 100 fs ultraviolet pulse to produce a fourth signal beam. Bencivenga et al., Nature 520, 205 (2015).   Read More Ultrafast demagnetization dynamics When an ultrashort optical laser pulse excites a magnetic material, it responds with an almost instantaneous reduction of its magnetization, followed by a slower recovery. This dynamics can be followed by time resolved magnetic holography, taking FEL images of samples excited by IR pulses. von Korff Schmising et al., Physical Review Letters 112, 217203 (2014).   Read More Holography with customizable reference Fourier transform holography retrieves microscopic images encoding in the X-ray scattered wave the interference between a known reference and the sample. The presented algorithm allows reconstruction from customizable references that can be designed in order to optimize signal from each particular sample, overcoming the limitations of standard holography geometries. Martin et al., Nature Communications 5, 4661 (2014).   Read More 0123456789

Coherent Diffraction Imaging proof of principle

In March 2012 the performance of the K-B mirror focusing optics, designed to provide a 3x5 µm² microprobe, reached some modest microprobe of 40×50 µm² with preserved coherence. This allowed us to perform the first proof-of-principle single-shot CDI and holography imaging of nano-lithographic test objects, fabricated on Si₃N₄ windows. The intensity of the photons scattered from the objects was monitored on a CCD camera using a detection set-up with a 45° multilayer (for 32.5 nm) mirror.The speckle pattern of the ‘Christmas tree’ object was obtained in a single-shot mode (pulse energy ~20 µJ and wavelength 32.5 nm). Although the object was destroyed by this intense FEL pulse, the information contained in the diffraction pattern was sufficient for reconstruction of the object image by recovering the missing phase information using computational algorithm. Similar successful CDI experiments with other test samples have confirmed that the Fermi@Elettra FEL-1 peak intensity, coherence and pulse duration are sufficient for performing ultrafast coherent diffraction imaging of non-periodic nano-objects, obtaining the necessary structural information before the radiation damage has occurred. 

First proof of principle CDI experiment performed at the DiProI beamline with an indirect detection geometry. The image is reconstructed through phase retrieval algorithm.

Magnetic and Resonant CDI

First proof of principle of resonant magnetic scattering performed at the DiProI beamline: the magnetic domain scattering is more intense at the Co M_2,3 resonance.

Absorption at the Co M2,3-edge. Blue dots represent wavelengths at which magnetic scattering patterns have been measured.

The proof-of-principle resonant CDI experiments were performed with Co/Pt multilayer samples, exploring the strong resonant enhancement of magnetic scattering at the Co M2,3-edge. For these experiments we installed and commissioned a direct detection CCD system (X-CAM) provided by our partner from CFEL-DESY. Tuning the Fermi-FEL wavelength λ to the Co M2,3 absorption edge (20.8 nm), the speckle pattern created by the photons scattered from the magnetic domains gains intensity. This ring structure is typical for a labyrinth-type domain organization and contains information about the average domain size and period of the magnetic structure. The extraordinary opportunities of circularly polarized Fermi-FEL pulses are in using single-shot resonant magnetic scattering in holography approach that will allow easier access to magnetic dynamic experiments.

Direct detection CCD system Modular CCD: the main unscattered beam is let through the gap between two chips.