Neuropathic pain (NP) is a chronic and disabling condition resulting from injury or disease of the somatosensory system. Characterized by sensory disturbances such as allodynia, hyperalgesia, and spontaneous pain, NP remains a major clinical challenge due to the limited efficacy and significant side effects of conventional pharmacological treatments. In recent years, photobiomodulation therapy (PBMT), also referred to as low-level laser therapy (LLLT), has emerged as a promising non-pharmacological strategy for managing NP. PBMT involves the application of red or near-infrared light to biological tissues, triggering a range of photochemical and photophysical responses that enhance mitochondrial function, reduce oxidative stress, modulate inflammation, and support neural repair. This review provides a comprehensive synthesis of the current evidence on PBMT for NP, integrating mechanistic insights with preclinical findings. We discuss the biological underpinnings of PBMT, including mitochondrial activation via cytochrome c oxidase, modulation of cytokines and oxidative stress markers, and upregulation of neurotrophic factors such as BDNF. Preclinical studies in well-established NP models (e.g., chronic constriction injury, spared nerve injury, diabetic neuropathy) demonstrate consistent analgesic effects and neuroprotective outcomes following both local and remote/systemic PBMT applications. We also highlight key limitations and knowledge gaps in the field, including the need for standardized protocols, greater exploration of remote PBMT strategies, and improved consideration of sex-based responses. Finally, we outline future directions, such as integration with multimodal therapies, personalized dosimetry, and the development of wearable and transcranial PBMT technologies. Together, the existing body of evidence supports PBMT as a safe and potentially effective tool for NP management, while underscoring the need for more rigorous and translational research.

Dopamine (DA) is one of the most important neurotransmitters in the human body, which is becoming a key breakthrough for addressing myopia, neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease, and mental diseases such as depression and schizophrenia. However, the activity of DA shows diurnal and seasonal variations, which may be due to the influence of solar activity time on the biological clock of the suprachiasmatic nucleus. By irradiating ARPE-19 cells with red and near-infrared light of different wavelengths, we studied and confirmed that the secretion and transformation of the light-induced neurotransmitter DA significantly depend on light wavelength and light dose. LED-chip light sources with emission peaks at 620, 680, 730, 800, and 850 nm and phosphor-converted LED light sources with emission peaks at 710 and 830 nm were used. It was confirmed that both the red and near-infrared light with variant wavelengths and doses can induce DA secretion to some extent. Yet, the concentrations of DA induced by the wideband spectral light of W710 and SW830 are higher than those induced by the narrowband single-LED-chip light and remain relatively stable under variant light doses. Among all the light sources, the model SW830 light source is the best one. This paper proposes a noninvasive way to induce the secretion of neurotransmitter DA and paves a reliable way to treat myopia, neurodegenerative diseases, and other diseases by using the neurotransmitter DA and the basic knowledge of photophysiology.

Reaching nanometric spatial resolution in terahertz (THz) nanoimaging provides a powerful tool for the characterization of photonic devices. Here, we couple a THz source to a conductive atomic force microscope to measure the THz photo-induced current with nanometric spatial resolution. We aim at measuring the THz photo-induced current of few-layer graphene flakes with a platinum nanometric probe that acts both as THz field-enhancement antenna and as metal counter-electrode that forms a nanojunction. The THz beam is generated at 0.61 THz by an amplifier-multiplier chain. THz photo-induced current signals are detected and compared with the current-voltage characteristics. With this method, we map nanometric charge puddles in few-layer graphene flakes, and observe evidence of THz rectification at the platinum-graphene nanojunction. The local junction characteristic can be used to assess the surface quality of 2D-material flakes.

Introduction:Surface-emitting terahertz quantum cascade lasers (THz QCLs) are highly promising for applications requiring high-quality far-field beams and controlled beam divergence. However, limited brightness and output power in conventional surface-emitting designs remain significant barriers to practical implementation. Although photonic crystal structures and distributed Bragg reflectors have been explored to enhance surface emission, intrinsic limitations in emission area scaling and brightness improvement persist. Thus, new strategies are essential to advance the performance of surface-emitting THz QCLs.Methods:This study proposes a plasma-assisted photonic crystal waveguide design to improve surface emission efficiency in THz QCLs. A three-dimensional TM-mode coupled wave theory (3D TM-mode CWT) model was developed, incorporating effective permittivity enhancement and a self-consistent iterative scheme to accurately simulate optical field distribution and interaction within the structure.Results:Simulations reveal that the introduction of a plasma layer effectively disrupts the optical field symmetry characteristic of conventional double-metal waveguides, promoting vertical emission. Through systematic optimization, a plasma layer thickness of 0.8 μm was identified as having the potential to achieve surface emission efficiencies exceeding those of conventional structures by over two orders of magnitude. This enhancement is realized without significantly increasing fabrication complexity.Discussion:The plasma-assisted photonic crystal waveguide design offers a viable pathway toward realizing high-brightness surface-emitting THz QCLs. Although challenges such as material growth control and thermal management remain, the substantial improvement in surface emission efficiency underscores the potential of this approach for future high-performance terahertz applications.

IntroductionThiarubrine A, a fascinating class of linear carbon chains, can be extracted from certain plants and are known for their photolabile pigment properties.MethodsIn this study, a modified Hückel method to investigate the optical properties of thiarubrine A has been employed, determining its absorption spectrum and wavelength-dependent complex refractive index. Additionally, using the nonequilibrium Green’s function formalism, the conductance of a single thiarubrine A molecule has been derived.Results and discussionLight absorption, complex refractive index dispersion, and conductance of thiarubrine A have been simulated. Exploiting its photolability, a light-induced switch in single-molecule conductance has been demonstrated through ultraviolet-visible irradiation, which produces a photoproduct containing a thiophene group. These findings enhance our understanding of the optical properties of naturally occurring polyynes and highlight their potential applications in single-molecule junctions for nanoelectronics.

Monitoring lungs functions is key for detecting several morbidities and pathologies. Photons in the 600–1,300 nm range might have the potential to reach lungs and provide compositional and functional information. Yet, few optical techniques have been challenged non-invasively so far. In this paper, we investigate the conditions to probe lungs using Time Domain Diffuse Optical Spectroscopy (TD-DOS). Counterintuitively, from Monte Carlo simulations we discovered that a higher absorption coefficient in the chest wall as compared to lungs increases sensitivity to deeper structures. In vivo measurements on the thorax of healthy volunteers during a forced breathing protocol, complemented with information on lung composition and previously evaluated in vivo spectra of porcine lung, suggest that this condition occurs above 1,100 nm. Multiple experimental setups were exploited to cover the 600–1,300 nm spectral range and test different source-detector distances (3–7 cm). All measurements exhibit oscillations consistent with the breathing rhythm, suggesting detection of lung expansion and compression. However, marked differences for different subjects and a complex dependence of the detected signal on the photon time-of-flight seem to allure to a non-trivial role of photon propagation through lungs, related–for instance–to the presence of alveoli and perhaps also to the overlying heterogeneous tissues. The unceasing development of time-resolved single-photon detectors with increasing performances above 1,000 nm, and a better understanding of lung optics–e.g., anomalous diffusion models–will help unravel the information from late, deep-travelling photons and lead to a novel photonic tool to probe the lungs non-invasively.

In this work, the first hyperpolarizability of Aux@Ag100-x core-shell nanoparticles with x the gold molar fraction in percent and the gold core of which is 12 nm in diameter, is determined and compared to that of their corresponding laser annealed nanoparticles using hyper Rayleigh scattering experiments. Laser annealing transforms the initially composite Aux@Ag100-x core-shell nanoparticles into alloyed AuxAg100-x homogeneous nanoparticles, providing a reference for comparison. It is observed that the evolution with the relative molar ratio between gold and silver of the first hyperpolarizability magnitude of both the Aux@Ag100-x core-shell and the alloyed AuxAg100-x nanoparticles is driven by the SPR resonance enhancement occurring at the harmonic wavelength due to red shifting of the SPR band away from the harmonic wavelength. Furthermore, the first hyperpolarizability magnitude of the Aux@Ag100-x core-shell nanoparticles is found to be about three orders of magnitude larger than that of the annealed alloyed AuxAg100-x nanoparticles. This feature may be attributed to the existence of the two nonlinearities, namely, the surface nonlinearity due to the surrounding medium–silver layer interface and the silver–gold metal - metal interface constructively contributing due to their close localization. The core-shell morphology is thus highly beneficial in view of applications as compared to the alloyed one.