Self-diffraction is a four-wave mixing process proportional to the square modulus of third-order nonlinearity susceptibility χ(3), which is related to the material's electronic and thermal properties. In this study, we investigate the wavelength dependence of the self-diffracted signal generated by a femtosecond pulsed laser in a dye solution to directly evaluate the electronic third-order nonlinear susceptibility spectrum. By accounting for absorption effects and phase matching conditions, we determine the |χ(3)| for different concentrations. Experimental results complemented with theoretical predictions show that, in the low absorption and thin sample limits, the signal reproduces the |χ(3)| spectral profile. These findings demonstrate the feasibility of measuring nonlinear susceptibility spectra arising solely from the bound-electronic response across a wide spectral range and for various compounds.

Membraneless compartmentalization via liquid-liquid phase separation (LLPS) has emerged as a powerful strategy to organize biochemical reactions. Recently, peptide-based coacervates demonstrated the potential to function as microreactors by enhancing reaction kinetics through increased local concentrations and altered microenvironments. Here, we introduce an O-methylated diphenylalanine-based tripeptide LLLPFF-OCH3 containing an N-terminal proline, designed to undergo LLPS, and simultaneously function as an enantioselective organocatalyst. Comprehensive characterization via confocal microscopy, fluorescence recovery after photobleaching (FRAP), micro-Raman and attenuated total reflection infrared (ATR-IR) spectroscopy, diffusion-surface plasmon resonance (D-SPR), and molecular dynamics (MD) simulations revealed the formation of stable liquid droplets. In contrast, a racemic mixture of LLLPFF-OCH3 and DDDPFF-OCH3 failed to form liquid droplets and instead formed a solid precipitate, unveiling a critical role of enantiopurity in LLPS. Proof-of-concept catalytic studies proved enantioselective organocatalytic activity of the LLLPFF-OCH3 liquid coacervates. Beyond catalysis these results may have broader implications in understanding prebiotic chemistry and neurodegeneration.

We investigate the mid-infrared chiroptical response of Aluminum-doped Zinc Oxide (AZO)-based plasmonic nanostructures incorporating pharmaceutical chiral drug solutions. We systematically examine plasmon-enhanced vibrational circular dichroism (VCD) of the chiral drug solution to develop efficient chiroptical sensing techniques.

We theoretically model third-harmonic generation in near-zero heterogeneous nanostructures arising from collision-driven nonlinear electron dynamics. We explore the potential of harmonic generation process on a sodium-aluminum bilayer for the development of integrated XUV sources.

The capability of anisotropic media to exert an optical torque on electromagnetic fields is crucial for polarization control. Here we investigate twisted layered stacks of uniaxial anisotropic media to engineer chiral mirrors for the manipulation of circularly polarized light by adjusting the layer number, thicknesses, and orientation. To this aim, we undertake a comprehensive theoretical analysis devising a multilayered twisted anisotropic photonic crystal enabling highly efficient circular polarization manipulation functionalities, i.e., showing concurring close-to-unitary helicity-preserving reflectance of one circular polarization and transmittance of the opposite one. Owing to the angular-momentum manipulation concept enabled by our proposed devices, we envisage that such chiral mirrors are promising candidates for an alternative class of integrated circular polarizers, holding great potential for applications in quantum technologies, polarization-sensitive optical detectors, and electro-optical information processing.

The enhancement of the inherently weak optical activity of solvated molecules by superchiral fields, crucial for detecting their chirality, is a research frontier of photonics and the basis of novel chiroptical detection schemes. Here, we show that an effective medium consisting of randomly dispersed metal-based nanoparticles embedded within an optically active solvated drug (aqueous reparixin) can enhance vibrational optical rotation and circular dichroism thanks to superchirality produced by slow light in near-zero index conditions. We evaluate from first principles the effective bianisotropic response of the bulk chiral effective medium, showing that, by adjusting the nanoparticles filling fraction, vibrational optical activity is greatly enhanced by a factor ≃ 10^2-10^3 at the near-zero index resonance. Our results are relevant for the development of innovative devices capable of detecting the chirality of low-volume samples, with applications in quantum chemistry and nanomedicine.

Polarization control is achievable through the optical torque exerted by anisotropic media. We engineer miniaturized uniaxial anisotropic stacks as chiral mirrors reflecting over 99% of one circular polarization and less than 1% of the opposite.

We investigate miniaturized and integrable stacks of uniaxial anisotropic layered media to engineer chiral mirrors for manipulating circularly polarized light thanks to the optical torque exerted by the medium polarization on an electromagnetic field.

We explore the potential applications of localized surface plasmon resonances (LSPRs) to investigate mid-infrared chiroptical response of Al-doped ZnO (AZO)-based nanostructures embedding layers of chiral pharmaceutical drug solutions to develop novel chiroptical sensing techniques.

We investigate the mid-infrared chiroptical response of plasmonic nanostructures based on Al-doped ZnO and layers of an aqueous solution of Ladarixin, a chiral pharmaceutical currently under clinical trial for the treatment of type 1 diabetes. We explore the possibilities offered by localised surface plasmon resonances (LSPRs) for the enhancement of vibrational circular dichroism (VCD) of the considered chiral drug solution. Focusing on diverse plasmonic nanoshell geometries, we find that LSPRs provide an amplification factor of VCD differential absorption cross-section ranging from [Formula: see text] to [Formula: see text] thanks to near-field intensity enhancement produced by LSPRs. Our results indicate that nanoshell LSPRs are promising for probing molecular chirality at the nanoscale.

We investigate resonant third-harmonic generation in near-zero index thin films driven out-of-equilibrium by intense optical excitation. Adopting the Landau weak coupling formalism to incorporate electron-electron and electron-phonon scattering processes, we derive a novel set of hydrodynamic equations accounting for collision-driven nonlinear dynamics in sodium. By perturbatively solving hydrodynamic equations, we model third-harmonic generation by a thin sodium film, finding that such a nonlinear process is resonant at the near-zero index resonance of the third-harmonic signal. Thanks to the reduced absorption of sodium, we observe that third-harmonic resonance can be tuned by the impinging pump radiation angle, efficiently modulating the third-harmonic generation process. Furthermore, owing to the metallic sodium response at the pump optical wavelength, we find that the third-harmonic conversion efficiency is maximised at a peculiar thin film thickness where evanescent back-reflection provides increased field intensity within the thin film. Our results are relevant for the development of future ultraviolet light sources, with potential impact for innovative integrated spectroscopy schemes.

The capability of near-zero-index media to bypass phase-matching requirements constitutes a promising platform for harmonic generation, which plays a crucial role for the development of compact ultraviolet radiation sources. Here, we investigate third-harmonic generation in near-zero-index heterogeneous nanostructures undergoing collision-driven nonlinear electron dynamics upon pulsed electromagnetic excitation. In particular, we model third-harmonic generation in sodium-aluminum bilayers by perturbatively solving Maxwell's equations in the undepleted pump approximation, finding that such a nonlinear process can become doubly resonant under the sodium and aluminum near-zero-index conditions for pump and third-harmonic waves, respectively. Furthermore, we find that third-harmonic generation is maximized at a peculiar pump incidence angle where attenuated total internal reflection enables surface plasmon polariton excitation at the sodium-aluminum interface.

We investigate the contribution of inelastic electron collisions to nonlinear (NL) dynamics in ultraviolet plasmonic nanoparticles, exploring their potential for harmonic generation. Employing the Landau weak coupling formalism to model radiation-driven electron dynamics in sodium and aluminum, we account for both electron–electron and electron–phonon scattering processes by a set of hydrodynamic equations, which we solve perturbatively to obtain third-order NL susceptibilities. Furthermore, we model high harmonic generation enhanced by localized surface plasmons in nanospheres composed of such poor metals, demonstrating their efficient operation for extreme ultraviolet generation. Our investigation reveals that plasmonic nanospheres composed of sodium and aluminum produce a large field intensity enhancement of ≃103–105, boosting the harmonic generation process. Our findings indicate that poor metals hold great promise for advanced extreme ultraviolet nano-sources with potential applications in nano-spectroscopy.

An experimental study about field emission properties of commercially available graphene flowers cloth is reported. Material characterization by means of X‐ray diffraction, Raman spectroscopy, and X‐ray photoemission spectroscopy confirms the formation of high quality vertical few‐layers graphene nanosheets. A tip‐anode setup is exploited in which nanomanipulated tungsten tip is used as the anode at controlled distance from the emitter in order to reduce the effective emitting area below 1 µm 2 , giving access to local characterization. A turn‐on field as low as 0.07 V nm −1 and field enhancement factor up to 32 for very small cathode–anode separation distances is demonstrated, in the range 400–700 nm. It is also shown that the turn‐on field increases for increasing distances, while the field enhancement factor decreases. Finally, time stability of the field emission current is reported, evidencing a reduction of the fluctuations for lower current levels.

Vanadium oxides have attracted research interest because their optoelectronic properties make them optically active with room-temperature photoluminescence (PL) emission, which, however, is not sufficiently intense for real applications. For this reason, many nanostructured vanadium oxides are currently fabricated through several precursors and different treatments to improve the PL efficiency and enhance the PL intensity. Herein, we propose an alternative and facile route to the fabrication of nanoporous vanadium oxide flakes through the spontaneous in-ambient degradation of layered van der Waals VI3 crystal, which is composed of a mixture of V2O5 and V3O7 phases. The as-grown VI3 crystals and the formed nanostructured vanadium oxide have been thoroughly studied using X-ray diffraction (XRD) and Raman spectroscopy to access the structural properties, X-ray photoemission spectroscopy (XPS) and synchrotron-based XPS to analyze the electronic core levels and valence bands, scanning electron microscopy (SEM) to access the morphology, and PL spectroscopy to grasp the optoelectronic properties. The nanoporous vanadium oxide system reveals an intense room-temperature PL emission in the red light visible range between 1.7 and 2.0 eV (620 and 730 nm), which is consistent with the V2O5 PL response. Remarkably, the PL emission reaches high intensity compared with those of different V2O5 nanostructures and is stable for months without intensity quenching and energy shifting. This discovery easies the integration of nanostructured vanadium oxides in optoelectronic nanodevices. Besides, the facile methodology proposed here promises to be applied to realize other nanostructured transition metal oxides.

Imidazole based eutectic solvents have been recently proposed as novel solvents and have been synthetized and characterized by different experimental techniques. We studied the structure of two deep eutectic solvents (DESs) based on imidazole and two organic salts (tetrabutylammonium bromide, TBABr, and choline chloride, ChCl). We focused our attention on the microscopic distribution of their components in the liquids by a study of Infrared and Raman spectroscopy and X-ray diffraction. The vibrational spectra of the eutectic mixtures have been analysed with the aim to characterized the nature of the interactions between anions, cations and imidazole. X-ray diffraction pattern has been interpreted on the light of the intermolecular contacts. Vibrational spectra and diffraction data have been compared with the results of computational studies obtained for both the DESs by molecular dynamics and quantum chemistry calculations.

•Doping monitoring of p-type Si via Raman spectroscopy with visible and UV excitations.•First-order Raman Stokes Si peak analysis via an improved Fano-like fitting model.•Illustration of a linear doping dependence of the wavelength-independent parameters.•Analysis of the excitation energy dependence of asymmetry reciprocal parameter q−1.•Demonstration of the full portability of Raman dopant monitoring to Si nano-devices.

The doping concentration of B doped single-crystal Czochralski Si(1 0 0) wafers (6 x 10(14)-5 x 10(19) cm(-3)) has been monitored via micro-Raman spectroscopy using visible (633 and 532 nm) and near-UV (355 nm) laser excitations at low power (5 mW). Data have been analysed with unprecedented accuracy via a convoluted FanoGaussian model of the first-order Raman Stokes mode of Silicon. This allowed the determination of the fitting spectral parameters (peak position and width) with an accuracy of 0.01 cm(-1), which enables a reliable probing of the concentration. We observed, independently on the excitation wavelength used, a widening (up to 6.5 cm(-1)), a frequency-softening (up to 1.5 cm(-1)) and an intensity reduction (down to 90%) of the Si peak with the doping concentration. The widening and frequency-softening follow a strictly linear dependence with doping concentration, allowing a calibration. A linear dependence of the reciprocal Fano asymmetry parameter (q(-1)) with excitation energy is verified, with the slope showing a linear behavior with the doping concentration and providing a direct estimate on the hole-phonon interaction strength. Results are reproduced with surfacesensitive near-UV Raman spectroscopy on BF2+ ion implanted and laser thermal annealed (LTA) Si, demonstrating the full portability of the Raman technique to state-of-the-art nanoelectronics.