Structured light as a tool for the formation and analysis of new states of matter

SUMMARY

Studying microscopic properties via interaction with photons or other particles yields valuable information about matter, which is used with advantage by many scientific disciplines, e.g. in chemistry, biology and physics, and they are also interesting for many technological fields. When passing through matter, photons transfer energy, momentum, as well as spin and spin momentum to the atoms. The spin angular momentum (SAM) of a light beam is related to its polarization, while the orbital angular momentum (OAM) is determined by the beam's spatial profile. For example, beams with helically shaped wavefronts have a well-defined OAM that points along the direction of beam propagation. Planning and performing the most basic experiments with optical vortex beams is a challenging task. The primary reasons for this can be attributed to the fact that efficient OAM transmission to atoms is hindered by zero intensity on the beam axis and that the transmission strongly depends on the distance of the atoms from the beam axis. Indeed, the atoms are highly localized with respect to the diameter of the beam carrying the OAM. Atoms that are displaced from the beam axis experience a light field typical of an ordinary Gaussian beam, while atoms near the optical axis, where the OAM value is sharply defined, experience a very small field. In addition, in a homogeneous target, the proportion of atoms close to the axis is small. Although transmission of optical OAM to photoelectrons seems unlikely, if it occurs it must be due to a new type of non-dipole transition associated with the OAM vector potential and could be used, for example, to induce magnetization in molecules. In the past, photon beams carrying non-zero OAM have already been prepared in the visible light region. In a recent project funded by the ARRS (J1–8134), we proposed: a) the development of efficient schemes that enable the preparation of extremely short-lived, spin-beams in the X-ray and short-wave ultraviolet (XUV) spectral regions with light sources based on on the generation of high harmonic components (HHG) in gases and with a free electron laser (FEL); b) conducting a fundamental experiment that demonstrates the transmission of OAM from a light beam to atoms. The project was successful. With this project, we want to take advantage of the unique properties of the resources we have set up and move from the first demonstration experiments to techniques for the preparation, control and diagnostics of new substances based on OAM transfer. The main goals of the scientific research we propose are summarized below: 1) We propose the development of a new method for the generation of a pulsed, directional, localized magnetic field with tunable duration (nanometer space scale, femto-nanosecond time scale). 2) We propose setting up a new method based on OAM light diffraction that will enable topological reconstruction of nanostructures and time-resolved research of magnetic helicoidal dichroism. 3) As a fundamental question related to the above, we plan to further examine the laws and practical possibilities that determine the transfer of OAM to atoms. To achieve these goals, we will use the long-term expertise of the groups of the University of Nova Gorica and the Jožef Stefan Institute. Cooperation will be strengthened by the support of the theoretical group of the University of Halle. Cooperation with the group from CEA Paris and the group from the University of Cergy Paris, as well as with the groups using the Fermi free electron laser in the Elettra Sincrotrone Trieste laboratory, is also planned. Experimental activities will be carried out by groups at the University of Nova Gorica, at the Jožef Stefan Institute and with the FERMI free electron laser at Elettra.

PROJECT’S TEAM

prof. dr. Giovanni De Ninno (UNG)
prof. dr. Barbara Ressel (UNG)
dr. Federico Galdenzi (UNG)

dr. Matjaž Žitnik (IJS)
dr. Andrej Mihelič (IJS)
dr. Klemen Bučar (IJS)

FINANCING

The project was funded by the “Javna agencija za raziskovalno dejavnost Republike Slovenije”.