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Team:
Permanent staff: Maurizio Sacchi, Yunlin Zheng, Franck Vidal
Post-doc: Pietro Carrara
ANR project HELIMAG (AttoLab, INSP, Synchrotron SOLEIL, Institut d’Optique, Spintec)
In addition to the spin angular momentum (SAM) associated to the photon polarization, LaguerreGaussian beams carry also an orbital angular momentum (OAM) of lhbar/photon associated to an azimuthally varying phase term exp(ilφ ). OAM laser beams found applications in fields as different as biology, telecommunication, imaging and quantum technologies. Their capability to exert a mechanical torque was exploited to create optical spanners for manipulating small particles. The azimuthal phase dependence introduces a singularity on the propagation axis and a radial modulation of the intensity (ring-shaped), properties that have been used to modify magnetic ordering, to improve the spatial resolution in microscopy, and to enhance the edge sharpness in phase contrast imaging.
More recent is the generation of OAM beams at shorter wavelengths, from XUV to hard x-rays, which are now finding an increasing number of applications, often based on extrapolations of previous work carried out in the visible range.
Our work concentrates on exploiting the fact that, as it happens for the SAM, the handedness imposed by the OAM can be used to perform x-ray spectroscopie studies of magnetic materials [1-4] and, more generally, of chiral systems.
The concept of Magnetic Helicoidal Dichroism (MHD) [1,2] is based on an extension of the better known Magnetic Circular Dichroism technique, and it has been developed with the objective of probing the topology [3] and ultrafast dynamics [ 4] of complex magnetic textures.
In a recent study [5], we also addressed the role of the OAM in ptychography, an imaging technique based on the analysis of coherent scattering, by comparing XUV images obtained by using radiation with different t values. Our results confirm that the attainable spatial resolution increases with t, and show that this extension of the use of OAM beams from the visible range to shorter wavelengths opens new perspectives for high-resolution element-selective x-ray imaging of magnetic structures.
Our experiments have been carried out at the FERMI free-electron laser source in Trieste and at the SOLEIL synchrotron in Saint-Aubin.
Main collaborations:
T. Ruchon (AttoLab-Lidyl Saclay), M. Fanciulli (Univ. Cergy), B. Dieny (Spintec Grenoble), F. Delmotte (Inst. d’Optique, Orsay), D. Dennetière, H. Popescu
(Synchrotron SOLEIL), M. Pancaldi, F. Capotondi, C. Spezzani, G. De Ninno (FERMI, Sincrotrone Trieste), R. Delaunay (LCP-MR Paris), F. Fortuna (ISMO Orsay).
Recent publications:
1. Electromagnetic theory ofHelicoidal Dichroism in reflection from magnetic structures, M. Fanciulli, D. Bresteau,
M. Vimal, M. Luttmann, M. Sacchi, T. Ruchon, Phys. Rev. A. 103, 013501 (2021). cnrs.hal.science/hal-03033113 l.
2. Magneto-optics with light beams carrying orbital angular momentum (OAM), T. Ruchon, M. Fanciulli, M. Sacchi, in The 2022 Magneto-optics Roadmap (A. Berger and P. Vavassori Eds. ), J. Phys. D: Appl. Phys. 55, 463003
(2022). cnrs.hal.science/hal-03765500/
3. Observation ofMagnetic Helicoidal Dichroism with Extreme Ultraviolet Light Vortices, M. Fanciulli, M. Pancaldi, E. Pedersoli, M. Vimal, D. Bresteau, M. Luttmann, D. de Angelis, P. Ribic, B. Rosner, C. David, C. Spezzani, M. Manfredda, R. Sousa, 1.-L. Prejbeanu, L. Vila, B. Dieny, G. de Ninno, F. Capotondi, M. Sacchi, T. Ruchon, Phys. Rev. Lett. 128, 077401 (2022). arxiv.org/pdf/2103.13697.pdf
4. Magnetic vortex dynamics probed by time-resolved Magnetic Helicoidal Dichroism, M. Fanciulli, M. Pancaldi, A.E. Stanciu, M. Guer, E. Pedersoli, D. De Angekis, P. Rebernik Ribic, D. Bresteau, M. Luttmann, P. Carrara, A. Ravindran, B. Rosner, C. David, C. Spezzani, M. Manfredda, R. Sousa, L. Vila, 1. L. Prejbeanu, L. D. BudaPrejbeanu, B. Dieny, G. De Ninno, F. Capotondi, T. Ruchon, M. Sacchi, Phys. Rev. Lett. 134, 156701(2025). journals.aps.org/prl/pdf/10.1103/PhysRevLett.134.156701
5. High-resolution ptychographic imaging at a seeded free-electron laser source using OAM beams, M. Pancaldi, F. Guzzi, C. S. Bevis, M. Manfredda, J. Barolak, S. Bonetti, 1. Bykova, D. De Angelis, G. De Ninno, M. Fanciulli, L. Novinec, E. Pedersoli, A. Ravindran, B. Rosner, C. David, T. Ruchon, A. Simoncig, M. Zangrando, D. E. Adams,
P. Vavassori, M. Sacchi, G. Kourousias, G. F. Mancini, F. Capotondi, Optica 11,403 (2024).
10.1364/0PTICA.509745
