European Laboratory for Non-Linear Spectroscopy

Stroke is a leading cause of long-term disability, frequently associated with persistent motor deficits. Gamma band oscillations, generated by synchronous discharge of parvalbumin-positive interneurons (PV-INs), are critically affected after stroke in humans and animals. Both gamma band and PV-INs play a key role in motor function, thus representing a promising target for poststroke neurorehabilitation. Noninvasive neuromodulatory approaches are considered a safe intervention and can be used for this purpose. Here, we present a novel, clinically relevant, noninvasive, and well-tolerated sub-acute treatment combining robotic rehabilitation with advanced neuromodulation techniques, validated in a mouse model of ischemic injury. During the sub-acute poststroke phase, we scored profound deficits in motor-related gamma band activity in the perilesional cortex. These deficits were accompanied by reduced PV-IN firing rates and increased functional connectivity, both at the perilesional and at the whole-cortex levels. Therefore, we tested the therapeutic potential of coupling robotic rehabilitation with optogenetic PV-IN-driven gamma band stimulation in a subacute poststroke phase during motor training to reinforce the efficacy of the treatment. Frequency-specific movement-related gamma band stimulation, when combined with physical training, significantly improved forelimb motor function. More importantly, by pairing robotic rehabilitation with a clinical-like noninvasive 40 Hz transcranial Alternating Current Stimulation, we achieved similar motor improvements mediated by the effective restoring of movement-related gamma band power, improvement of PV-IN maladaptive network dynamics, and increased PV-IN connections in premotor cortex. Our research introduces a new understanding of the role of parvalbumin-interneurons in poststroke impairment and recovery. These results highlight the synergistic potential of combining perilesional gamma band stimulation with robotic rehabilitation as a promising and realistic therapeutic approach for stroke patients.

Abstract We demonstrate the possibility of using 3D‐printed, see‐through planar elements built with commercially available materials as fluorescent Optical Antennas (OAs) for fast Optical Wireless Communication (OWC). OWC represents a key technology in the forthcoming next‐generation communication services (6G), given its intrinsic combination of bandwidth (BW), security, and pervasiveness. In the Visible Light Communication (VLC) approach, ubiquitous white or colored LED sources can also be used as optical transmitters besides providing indoor/outdoor illumination and signaling, strongly fostering the implementation of the Internet of Things (IoT) paradigm. Here, the intrinsic optical properties (such as BW, field of View (FoV), and collection efficiency) of four different fluorescent slabs grown with commercial, non‐optical resins typically employed to realize transparent objects are fully characterized, unveiling for the first time their large potential as receivers in VLC applications. Complete VLC communication tests are reported, demonstrating attainable bit rates larger than 70 Mb s −1 with On‐Off Keying (OOK) modulation, which could be largely increased toward the Gb s −1 target exploiting high‐order modulation schemes. This work can have a profound impact toward the full‐fledged implementation of the IoT paradigm, showing that transparent 3D‐printed objects can be exploited as optical front ends in a new class of VLC and OWC receivers.

The intensity noise of a laser source represents one of the key factors limiting the ultimate sensitivity in laser-based systems for sensing and telecommunication. For advanced applications based on interferometry, the availability of a shot-noise-limited local oscillator is even more important for the effective feasibility of high-precision measurements. This is particularly crucial in quantum optics applications based on homodyne detection schemes to measure non-classical light states, such as squeezed states. This work deeply investigates and analyzes the intensity noise features of the most widely used mid-infrared semiconductor heterostructured lasers: quantum cascade and interband cascade lasers. For this purpose, a comprehensive comparison of three different continuous-wave lasers operating at room temperature around 4.5 µm wavelength is presented. First, a thorough electro-optical characterization is given, highlighting the differences and the shared common characteristics of the tested devices. Then, a detailed intensity noise analysis is reported, identifying their different noise operations with a particular reference to shot-noise-limited operations. Finally, some perspectives towards advanced applications are discussed.

Free-space quantum key distribution (QKD) represents a groundbreaking advancement in secure communication, enabling secure key exchange over vast distances and offering robust encryption for the future quantum internet. However, the compatibility between fiber and free-space infrastructures continues to pose challenges for QKD protocols. Indeed, free-space and fiber-based networks commonly use different wavelengths and qubits encoding schemes. On the one hand, free-space QKD typically exploits visible light for its beneficial beam divergence compared with longer wavelengths, and polarization encoding for its robustness against turbulence. On the other hand, fiber-based QKD employs infrared light, particularly the C-band, because it shows the minimum losses with silica fibers, and time-bin encoding, due to polarization instability in optical fibers. In our study, we demonstrate the viability of a time-bin encoded QKD protocol operating in the C-band through horizontal turbulent free-space channels. We test the setup into a 50-m- and a 500-m-long link, respectively achieving an average secure key rate of 793 kbps and 40 kbps over several hours of measurements. The results encourage further exploration of the interoperability between free-space and fiber-based infrastructures, opening new possibilities for connecting terminal users with satellites in hybrid infrastructures.

Identifying novel and accessible therapeutic targets for Parkinson’s Disease (PD) remains a pressing goal. Growing evidence implicates cortical dysfunctions in PD-related symptoms, yet the mechanisms—especially those involving parvalbumin-positive interneurons (PV-INs), key regulators of brain oscillations and plasticity—are not fully understood. In this study, we investigate how PD alters PV-IN network and cortical oscillatory dynamics using the 6-hydroxydopamine (6-OHDA) mouse model. Through an integrated approach combining electrophysiological recordings, wide-field calcium imaging, and histological analysis, we reveal a profound cascade of cortical changes. These include pathological hyperactivity above 100 Hz during movement and severe disruptions in PV-IN connectivity across the motor cortex. Synaptic imbalances and microglial activation further point to a multifaceted cortical response to dopaminergic degeneration, revealing inhibitory dysfunction, oscillatory instability, structural remodeling, and neuroinflammation. Our results link PD to cortical instability and highlight cortical plasticity as a promising target for therapeutic intervention.

High-pressure polymerization of CS2 leads to structurally and stoichiometrically disordered solids, making characterization of the products and of reaction mechanisms challenging. This is due to the multiplicity of chemical pathways that CS2 is subject to in the free space. We reduced this multiplicity by constraining polymerization in a confined space. We inserted liquid CS2 in the one-dimensional pores of the all-siliceous zeolite Theta-One, subjected the mixture to maximum temperatures and pressures of 250 °C and 14 GPa, and recovered a darkened sample at ambient conditions. Synchrotron X-ray diffraction was performed on the materials. Full structural refinements, using ab initio calculated structures as starting models, show that CS2 in the zeolite undergoes selective topotactic polymerization, resulting in the ordered trans-isomer of the long-sought-after Bridgman's black polymer (-(C═S)-S-)n. We provide physical insight into the reaction mechanism by proposing that it consists of a molecular bending followed by addition. The trans-polymer forms spontaneously from the unstable, confined monomer upon relaxation in ab initio calculations.

Hydrazones are among the most promising newly developed photochromic molecules, often exhibiting very high isomerization quantum yields, long and tunable half-lives and excellent photostability. It has recently been demonstrated that substitutions on the hydrazone core with electron donating (EDG) or withdrawing (EWG) groups on either the rotor or stator moiety can greatly influence their photoswitching properties, in some cases conferring new and interesting properties onto them, such as emission toggling and two-photon activity. Here, we analyze the photodynamic behavior of three representative substituted hydrazones in depth, using ultrafast visible and infrared transient absorption spectroscopies, and perform density functional theory calculations to interpret their steady-state spectra. In particular, we focus on systems having an EDG and/or EWG substituent on the stator and rotor moieties, whose principal effect is to red shift the absorption spectra of the Z and E isomers relative to the parent unsubstituted hydrazone. Our results highlight the effect that substituents have on the isomerization and emission mechanisms of the hydrazones, and subsequently on their spectroscopic properties. Moreover, these studies elaborate on how the substituents and solvent polarity play important roles in altering the isomerization quantum yield.

Two complex π-expanded diketopyrrolopyrroles (EDPPs) have been prepared following a multistep but straightforward strategy. We discovered that the fate of these molecules in the excited state can be controlled by subtle differences in their structure. When NO2 groups are located at a distant position, the quadrupolar, centrosymmetric dye exhibits strong red emission across the solvents' polarity scale. However, when NO2 groups are adjacent to the lactam moiety, the EDPPs exhibit negligible emission even in non-polar solvents. Density functional theory (DFT) calculations indicate that the primary distinction between the two molecules lies in the structural planarity. The molecule with NO2 groups adjacent to the lactam moiety exhibits a loss of planarity due to the coulombic repulsion between these groups. The calculations also suggest that the nitro group does not participate in the S0 → S1 excitation. Furthermore, for both compounds, the first two excited states (one bright and one dark) are found to be very close in energy. The change in molecular geometry affects the non-radiative deactivation of excited states, leading to the two distinct emission behaviors. Experiments in a glassy solvent at low temperatures reveal that at 77 K the photophysics of both dyes becomes the same, which proves that thermal activation is the key mechanism for the non-radiative decay of the excited state for non-emissive EDPPs.

Transport processes underpin a wide variety of phenomena, ranging from chemistry, to physics and ecology. Despite their pervasiveness, however, several distinctive features of these processes are still elusive, making it difficult to recognize and classify the associated transport regimes. Using light scattering as a probe to explore different propagation regimes, we report on the experimental observation of non-self-similar light transport through turbid membranes. Our results show that a breakdown of self-similarity can arise for light waves even in the presence of isotropic and homogeneous disorder, and can be tuned by varying the turbidity of the system. By introducing the concept of self-similarity for light propagation, we provide a unified framework for the classification of light transport regimes—overcoming the dichotomy between normal and anomalous diffusion—and show that non-self-similar propagation is a common and experimentally accessible phenomenon. This insight can help to understand and model other scenarios where light transport is dominated by rare propagation events, such as in nonlinear and active media, but also in other fields of research beyond optics. Published by the American Physical Society 2024