Assisted by the ultimate light manipulation properties offered by flat optical devices, we developed different schemes to impart orbital angular momentum on several beams that originate wavepackets with controllable spatial and temporal distributions.

Spontaneous Four Wave Mixing (SFWM) which generates photonic pairs is studied if it is addressed by optical vortices carrying an orbital angular momentum (OAM). We show that the output beams are OAM-correlated and that the entanglement depends on the 4-level scheme used to realize SFWM.

We exploit gas-phase molecules as light-matter interface to store an orbital angular momentum (OAM) or a superposition of OAM states (OAM-based photonic qubits) carried by ultrashort laser pulses. The interplay between spin angular momentum and OAM is exploited to encode the amplitude and spatial phase information of light beams into rotational coherences of molecules. This last is restored on-demand over tens of picoseconds with a reading beam by taking advantage of field-free molecular alignment. The underlying mechanism at the origin of the storage can be interpreted by the spatial structuring of the molecular sample induced by the field. The excitation indeed produces an inhomogeneous spatial distribution of molecular alignment (amplitude & orientation) whose periodical revivals associated with the quantum beatings of the rotational wavepacket enables to restore the spatial beam structure on-demand. The strategy is successfully demonstrated in CO2 molecules at room temperature. Besides applicability as storage medium with THz bandwidth application, the use of molecules as light-matter interface opens new functionalities in terms of optical processing and versatile control of OAM fields.

Fully polarized light, cylindrical vector beams, and beams with opposite orbital angular momentum (OAM) and their superpositions are respectively represented as points on the Poincaré sphere (PS), the higher-order Poincaré sphere (HOPS) and the OAM Poincaré sphere (OAMPS). Here, we study the mapping of inner points between these spheres, which we regard as incoherent superpositions of points on the surface of their respective sphere. We obtain points inside the HOPS and OAMPS by mapping incoherent superpositions of points on the PS, i.e., partially polarized states. To map points from the PS to the HOPS, we use a q-plate, while for mapping points from the HOPS to the OAMPS, we use a linear polarizer. Furthermore, we demonstrate a new polarization state generator (PSG) that generates efficiently partially polarized light. It uses a geometric phase (GP) blazed grating to split an unpolarized laser into two orthogonal polarization components. An intensity filter adjusts the relative intensity of the components, which are then recombined with another GP grating and directed to a waveplate, thus achieving every point inside the PS. The proposed PSG offers advantages over other methods in terms of energy efficiency, ease of alignment, and not requiring spatial or long-time integrations.

Several types of super-resolution microscopy, such as Stimulated Emission Depletion (STED), Reversible Saturable Optical Fluorescence Transitions (RESOLFT) or Switching Laser Mode (SLAM) microscopies, employ Laguerre-Gaussian beams (also called vortex or doughnut beams) to obtain fluorescence information within a sub-wavelength region of the specimen under observation, thus breaking the diffraction limit and producing images of greatly improved quality. However, in general, these techniques operate on a point-by-point basis, so we need to raster scan the sample in order to build a full, meaningful image, which takes time. Parallelization of the illumination is the only way to make these microscopies more suitable for live cell imaging applications. Here, we demonstrate the parallel production of arbitrary arrays of Gaussian and Laguerre-Gaussian lasers foci suitable for super-resolution microscopy, together with the possibility to fast scan through the sample, by means of acousto-optic spatial light modulation, a technique that we have pioneered in the past in several other fields.