Recording the temperature-dependent luminescence emitted by an isolated single nanoparticle offers one strategy for performing far-field optical thermometry with spatial resolution below the diffraction limit. However, such measurements are inherently restricted to probing the temperature at a single spatial point. Here, we demonstrate an approach to sampling temperature gradients at multiple points within a subdiffraction region by simultaneously collecting the emission from different nanoparticle species with spectrally orthogonal temperature-dependent luminescence. Taking advantage of the narrow spectral bands and wavelength tunability of lanthanide-doped upconverting nanoparticle (UCNP) emission, we use a single laser to excite both NaYF:Yb,Er and NaYF:Yb,Tm UCNPs and concurrently acquire their spectrally distinct temperature-dependent luminescence. The emission spectra and temperature response obtained from tandem UCNP pairs consisting of one NaYF:Yb,Er and one NaYF:Yb,Tm UCNP are in excellent agreement with corresponding measurements using isolated individual UCNPs of each composition. To demonstrate the utility of this approach, we use a tandem pair of UCNPs located ∼108 nm from each other to probe the sharp temperature gradient resulting from laser heating of an isolated silver nanodisk. While the diffraction-limited emission spots of the UCNPs overlap nearly completely, we can distinguish a temperature difference of ∼19 K between their two locations. This capability is particularly applicable to scenarios that would benefit from multiple temperature data points, but where the majority of the sample surface must remain accessible for other purposes, such as in the case of plasmonic and photothermal catalysis.

The controlled generation and accurate characterization of light beams carrying orbital angular momentum (OAM) are essential for emerging applications in optical communication, quantum information, and advanced imaging. Metasurfaces offer a versatile platform for tailoring such structured electromagnetic fields. However, the accurate measurement of wavefronts containing multiple phase singularities remains a significant metrological challenge. In this work, we employ quadriwave lateral shearing interferometry (QLSI) as a quantitative phase imaging technique to retrieve spatially resolved phase maps of OAM beams generated by metasurfaces. We demonstrate that QLSI enables robust reconstruction of perfect and imperfect singular phase profiles, providing a reliable tool for the characterization of complex optical fields. This methodology is applied to evaluate metasurfaces designed using two distinct phase encoding mechanisms: effective refractive index (ERI) modulation and Pancharatnam-Berry (PB) phase. Comparative analysis reveals superior phase accuracy and enhanced fabrication tolerance in PB-based metasurfaces relative to ERI counterparts. These results highlight the potential of QLSI as a diagnostic and validation tool for structured light generation in next-generation photonic devices.

Mass density is a vital property for the improved biophysical understanding of and within biological samples. It is increasingly attracting active investigations, but still lacks reliable, noncontact techniques to accurately characterize it in biological systems. Contrary to popular belief, refractive index information alone is insufficient to determine a sample's mass density, as we demonstrate here theoretically and experimentally. Instead, we measured the nonlinear gain of stimulated Brillouin scattering to provide additional information for the mass density estimation. This all-optical method reduces the estimation error 10-fold, offering a more accurate and universal technique for mass density measurements.

Human-induced pluripotent stem cell (hiPSC)-derived neurons offer a powerful platform for replicating key aspects of human neurodevelopment, synaptic connectivity, and ion channel expression. However, their electrophysiological investigation remains challenging, particularly for studies aiming to elicit neuronal activity with minimal perturbation of physiological conditions. In this study, we integrated plasmonic gold pyramids onto commercial titanium nitride (TiN) microelectrode arrays (MEAs). The presence of these plasmonic structures enhanced the generated photocurrent by more than 30-fold and simultaneously reduced the electrode impedance by approximately 6-fold. Leveraging the unique optical properties of plasmonic nanostructures, we demonstrate that gold pyramids enable efficient neuronal photostimulation at low light intensities with minimal perturbations. Our approach combines nongenetic optical stimulation with high-resolution electrophysiological recording, providing precise spatiotemporal control of neuronal activity. These advances highlight the potential of our plasmonically enhanced MEA technology to bridge the gap between preclinical research and human neurological applications.

Identifying the handedness of chiral molecules is of fundamental importance in chemistry, biology, pharmacy, and medicine. Nanophotonic structures allow us to control light at the nanoscale and offer powerful tools for chiral sensing, enabling the detection of small analyte volumes and low molecular concentrations by harnessing optical resonances. Most existing strategies rely on intuitive concepts such as strong local field enhancement or large local optical chirality, often achieved by engineering electric and magnetic Mie resonances in dielectric or plasmonic nanostructures. Recent insights, however, reveal that the chiroptical response of resonant systems can be governed also by less obvious mechanisms such as modal crosstalk. In this work, we present a dielectric metasurface engineered to amplify the modal crosstalk by supporting two nearly degenerate, high-quality-factor resonant states known as quasi-bound states in the continuum. Our theoretical and numerical analysis predicts a pronounced differential transmittance that exceeds the detection threshold of standard spectrometers. In particular, the differential transmittance reaches up to 10 for the Pasteur parameter κ = 1 × 10. These findings advance the capabilities of nanophotonic sensors for chiral detection, paving the way toward ultrasensitive identification of molecular handedness in small volumes and concentrations within the experimentally detectable ranges.

We demonstrate circularly polarized photoluminescence emission, with dissymmetry factors over 0.1, from achiral organic dye molecules by leveraging quasi-bound states in the continuum (quasi-BICs) and surface lattice resonances (SLRs) in intrinsic silicon chiral metasurfaces. We find that the associated with the quasi-BIC mode remains robust against variations in the emission angle and dye thickness due to its strong lateral field confinement. In contrast, the of the SLR mode exhibits sign inversion depending on the emission energy and the dye layer thickness. The experimental results are supported by mode decomposition analysis, helicity density analysis, and the near-field spatial distribution of the electric field. These findings illustrate the relevance of the emitter's layer thickness in optimizing the emission of circularly polarized light. They also elaborate on the robustness of chiral quasi-BICs by comparing the of SLRs and quasi-BICs, offering insights into chiral light-matter interactions and advancing the design of circularly polarized light-emitting devices.

Two-photon sub-bandgap photocurrent (TPPC) is demonstrated in surface-nanotextured black diamond films fabricated by a two-step femtosecond laser treatment at an optimal total accumulated laser fluence of 5.0 kJ cm, unequally split between the two steps with a split ratio of 2:1. A broad intermediate band of electrically active deep-level defects, located at an energy distance of 1.83 eV from the conduction band, is experimentally observed by sub-bandgap spectral response evaluation in the 190-1000 nm wavelength range, allowing for a significant enhancement of quantum efficiency under photovoltaic conditions. This work represents the first experimental demonstration of TPPC in bulk materials with deep-level impurities conceived for intermediate-band solar cells and provides a solid physical interpretation of the operating principle of defect-engineered black diamond-based devices for solar energy conversion.

Laser-light sails are a spacecraft concept, wherein lightweight "sails" are propelled by high-intensity lasers. We investigated the near-infrared absorption of free-standing membranes of stoichiometric silicon nitride (SiN), a candidate sail material. To resolve the small but nonzero optical loss, we used photothermal common-path interferometry (PCI), for which we developed a self-referencing modality where a PCI measurement is performed twice: once on a bare membrane, and a second time with monolayer graphene deposited on the membrane. The graphene increases the absorption of the sample by orders of magnitude, such that it can be measured by ellipsometry without significantly affecting the thermal properties. We measured the absorption coefficient of SiN to be (1.5-3) × 10 cm at 1064 nm, making it a suitable sail material for laser intensities as high as ∼10 GW/m. By comparison, silicon-rich "low stress" SiN ( ∼ 1), with a measured absorption coefficient of approximately 8 cm, is unlikely to survive such high laser intensities. Our self-referencing technique enables the testing of low-loss membranes of various materials for laser sails and other applications.

At optical frequencies, interactions of the electric field component of light with matter dominate, whereas magnetic dipole transitions are inherently weak and challenging to access independently of electric dipole transitions. However, magnetic dipole transitions are of interest, as they can provide valuable complementary information about the matter under investigation. Here, we present an approach which combines structured light irradiation with tailored sample morphology for enhanced and high-contrast optical magnetic field excitation, and we test this technique on Eu ions. We generate spectrally tunable, narrowband, polarization-shaped ultrashort laser pulses, which are specifically optimized for the spectral and the spatial selective excitation of magnetic dipole and electric dipole transitions in Eu:YO nanostructures integrated into a metallic antenna. In the presence of the metallic antenna, the excitation with an azimuthally polarized beam is shown to provide at least a 3.0-4.5-fold enhancement of the magnetic dipole transition as compared to a radially polarized beam or a conventional Gaussian beam. Thus, our setup provides new opportunities for the spectroscopy of forbidden transitions.

Squaraine thin films are emerging as functional optoelectronic elements because of their anisotropic optical properties in the visible to near-infrared spectral range, which include characteristic properties such as large Davydov splitting, hybrid Frenkel-charge transfer excitons, and giant circular dichroism. The prototypical squaraine 2,4-bis-[4-(-diisobutylamino)-2,6-dihydroxyphenyl]-squaraine (SQIB) condenses into two different polymorphs (orthorhombic and monoclinic unit cells), both with distinct optical, electronic, and morphological properties. Polarized Raman microscopy spectra can distinguish between these polymorphs and indicate their crystallographic alignment, similar to polarized transmission spectroscopy, while atomic force microscopy precisely maps all topographical features. During crystallization, periodic nanodunes with cracks and protrusions along the local -axis can form from the orthorhombic SQIB polymorph without any lithographic steps. The full dielectric tensor is known for this polymorph, and the components of the real part are strongly negative near the absorption bands. For metallic nanoparticles, it is known that a negative dielectric function can lead to localized surface plasmons and field confinement. In this study, we investigate which of the morphological featuresnanodunes, cracks, or protrusionshave the potential to influence the excitonic properties in a similar enhancing fashion.

We demonstrate a new method of aligning liquid crystals along polymer surfaces that are printed vertical to the focal plane using direct laser writing. The method is based on nanogrooves that are imprinted into surfaces of polymer structures and provide robust, reliable, repeatable, and well-controlled alignment patterns. Our results demonstrate that the anchoring strength of a liquid crystal on printed nanogratings is comparable to that of conventional polyimide layers. The advantages are at least 2-fold. First, we can print large vertical areas of well-defined patterns of nanogrooves with uniform anchoring strength, and, second, we can control the azimuthal anchoring strength by adjusting the amplitude and the periodicity of nanogrooves. Printing of alignment nanogrooves on tilted, curved and surfaces of arbitrary shape could be realized using printing protocols based on the principle shown here with potential applications in emerging microphotonic devices based on liquid crystals.

We present superconducting nanowire photodetectors based on hBN-encapsulated, few-layer NbSe, showing signatures of single-photon sensitivity. The top-down fabrication process preserves the superconducting properties of NbSe, as confirmed by low-temperature transport measurements showing comparable results to unpatterned sheets, and it maintains a contact and wiring resistance down to ∼30 Ω at = 4 K. Meandered NbSe nanowires exhibit high responsivity (up to 4.9 × 10 V/W) over a spectral range of 650-1550 nm in a closed-cycle cryostat at 4 K, outperforming samples with different geometries in this work. The meander achieves a recovery time of (135 ± 36) ns, a system timing jitter of (1103 ± 7) ps, and a detection efficiency of ∼0.01% at 0.95 . A linear increase of the count rate with the number of photons between the noise level and the latching threshold offers a signature of single-photon sensitivity at 1100 nm.

Broadband photodetectors (PDs) are essential for various applications, including optical communication, sensing, and imaging. Modern semiconductor PD technologies often face challenges related to spectral coverage, power consumption, complex manufacturing, and limited integration with silicon electronics. As photonics technologies continue to advance alongside growing performance demands, exploring new avenues for innovative, cost-effective broadband PDs with reduced power consumption and manufacturing complexity is becoming increasingly important. In this work, we present a zero-bias, waveguide-integrated PD based on single-layer MoS, which operates at telecom wavelengths with no dark current. By utilizing the photothermoelectric effect combined with internal photoemission process, our devices demonstrate a record responsivity of ∼180 V/W at 1550 nm, the highest reported in the literature for unbiased 2D PDs operating in the short-wave infrared. The recorded frequency response is in the millisecond range, limited by the electrical RC time constant. The PD noise equivalent power is ∼500 nW at 1 Hz, dominated by 1/ noise, and is reduced to ∼0.3 nW at the Johnson limit. Consequently, the specific detectivity (*) is estimated to be ∼10 Jones at the 1/ limit, reaching ∼2 × 10 Jones at Johnson noise-limited operation. Our findings contribute to developing high-efficiency broadband MoS PDs and emphasize the potential of 2D semiconductors in advancing self-powered PDs technology.

Tunable metasurfaces enable active and on-demand control over optical wavefronts through the reconfigurable scattering of resonant nanostructures. Here, we combine novel insights inspired by mechanical metamaterials with the unique sensitivity of nonlocal optical resonances to interparticle distances to achieve giant tunability in mechano-optical metasurfaces where the mechanical metamaterial and optical metasurfaces are integrated in a single nanopatterned material. In a first design, judiciously engineered cuts in a flexible substrate enable large, strain-induced extension of the interparticle spacing, tuning a high-quality-factor resonance in a silicon nanoparticle array across a very broad spectral range. In a second design, we eliminate the substrate and demonstrate a nanopatterned silicon membrane that simultaneously functions as a mechanical metamaterial and an optical metasurface with large tunability. Our results highlight a promising route toward active metasurfaces, with potential applications in tunable filters, reconfigurable lenses, and dynamic wavefront shaping.

We demonstrate that dielectric Mie scatterers, in the form of silicon nanoparticles (SiNPs), can enhance both the performance and esthetics of semitransparent photovoltaic devices. Unlike plasmonic metal counterparts, dielectric SiNPs exhibit lossless, narrow-band, spectral, and spatially tunable scattering in the visible spectral range. Their effect on a luminescent solar concentrator (LSC) with high visible light transparency is analyzed both theoretically and experimentally as a model system. By selectively reflecting a specific spectral band, SiNPs increase the optical path length of solar photons within the active layer, leading to improved absorption and hence device efficiency. Simultaneously, this light management strategy ensures transmitted color neutrality, an important requirement for wider acceptance of semitransparent photovoltaics. Numerical simulations show that in the regime of individual SiNPs with diameters around 160 nm, a submonolayer surface coverage of ∼10% is sufficient to achieve color neutrality, at the same time enhancing photocurrent by 10-15% for an LSC device. Experimentally, such a dispersed SiNP layer on an LSC substrate is realized by depositing NPs with the surface capped by a sacrificial polymer shell. Subsequent etching of the shell by oxygen plasma leads to an LSC device with a functional selective scattering layer in line with theoretical predictions.

Biochemical sensing platforms have become indispensable to critical decision-making across healthcare, security, and industrydelivering essential data that powers AI systems and shaping our modern lifestyles. This growing reliance on biosensors has elevated expectations, creating demand for portable, user-friendly, and cost-efficient platforms with ultrahigh sensitivity and specificity. Nanophotonic biosensors, which harness engineered subwavelength architectures to amplify light-matter interactions, offer transformative solutions through label-free, real-time, multiplexed detection capabilities. Despite compelling laboratory demonstrations, these technologies remain largely unrealized in real-world applications. This perspective examines the critical "valley of death" in technology transfer, where promising innovations stall before commercialization, while drawing strategic insights from surface plasmon resonance biosensors' successful commercialization journey. Highlighting technologies engineered for high-demand applications, we advocate an application-guided design approach to unlock nanophotonic sensors' translational potential. We share our perspectives on how this strategic framework offers a pathway through commercialization bottlenecks, accelerating the transformation from scientific achievement to societal impact.

Spatial and temporal light modulation is a well-established technology that enables dynamic shaping of the phase and amplitude of optical fields, significantly enhancing the resolution and sensitivity of imaging methods. Translating this capability to electron beams is highly desirable within the framework of a transmission electron microscope (TEM) to benefit from the nanometer spatial resolution of this instrument. In this work, we report on the experimental realization of a photonic-based free-electron modulator integrated into the column of two ultrafast TEMs for presample electron-beam shaping. Electron-photon interaction is employed to coherently modulate both the transverse and longitudinal components of the electron wave function (through lateral phase imprinting and temporal profiling, respectively), while leveraging dynamically controlled optical fields and tailored designs of the electron-laser-sample interaction geometry. Using energy- and momentum-resolved electron detection, we successfully reconstruct the shaped electron wave function at the TEM sample plane. These results demonstrate the ability to manipulate the electron wave function before probing the sample, paving the way for photonics-inspired imaging and spectroscopy techniques in ultrafast electron microscopy.

Visualizing the behavior of complex laser systems is an outstanding challenge, especially in the presence of nonlinear mode interactions. Hidden features, such as the gain distributions and spatial localization of lasing modes, often cannot be revealed experimentally, yet they are crucial to determining the laser action. Here, we introduce an experimental lasing spectroscopy method that visualizes the gain profiles of the modes in a complex, disorderly coupled microring array laser using an artificial neural network. The spatial gain distributions of the lasing modes are reconstructed without prior knowledge of the laser device. We further extend the neural network to a tandem neural network that can control the laser emission by matching the modal gain/loss profile to selectively enhance the targeted modes. This mode visualization method offers a new approach to extracting hidden spatial mode features from photonic structures, which could improve our understanding and control of complex photonic systems.

Photon entanglement, a key feature of quantum correlations, provides a level of coherence absent in classical correlations, potentially offering new information when interacting with biological matter. One promising application is using entanglement decoherence to distinguish between healthy and diseased samples. However, achieving this requires efficient entangled photon sources capable of surviving through biological samples for reliable detection. In this work, we show the applicability of a polarization-entangled photon source as a label-free diagnostic tool for distinguishing between transgenic mouse models of amyloidosis and tauopathy and their respective control strains. We investigated cortical and hippocampal regions of these models, and our findings revealed greater preservation of entanglement in the transgenic samples compared to controls. To further enhance classification accuracy, we employed a supervised machine learning approach, achieving reliable distinctions between disease and control groups in unseen test samples. The quantum-based results were further validated through confocal imaging of the transgenic and control samples. These findings suggest that quantum sensing could serve as a label-free approach for distinguishing biological samples, with potential applications in the study of neurodegenerative disorders.

The responsivity of graphene-based photodetectors can be improved by forming heterostructures with other 2D materials and by further coupling to nanoparticles or quantum dots. In this study, we demonstrate that the photoresponse of a Graphene/MoSe/Graphene photodetector can be further enhanced by an external WS bilayer acting as a light-harvesting antenna. The WS bilayer is positioned outside the electronic pathway; thus, it does not directly contribute any photoexcited carriers. However, we observe a responsivity enhancement of up to 18 times, which can be explained by energy transfer from WS to graphene and the MoSe layer. Harnessing the excitonic properties of transition metal dichalcogenides (TMDs) as optical antennas defines a new strategy for photodetection.

The resolution of a classical imaging system is limited by diffraction. This limit can be overcome, for example, by implementing various forms of localization microscopy in which the center of a fluorescence distribution is estimated to an accuracy scaling with the square root of the number of detected photons, . In quantum imaging the object can be illuminated using correlated photon-pairs, leading early work to suggest that a improvement could be obtained as a result of averaging the position of = 2 events. However, similar to quantum lithography, which relies upon quantum illumination using entangled photon-pairs and two-photon absorption, the minimum resolvable feature size is reduced by a factor of 2, not just . Quantum imaging schemes can also lead to a factor of 2 improvement. By using a similar source of correlated photon-pairs to illuminate an object, a single-photon sensitive camera to detect the photon-pairs, and an image processing algorithm to record and sum the bisector positions of the transmitted photon-pairs, we realize a similar factor of ×2 improvement in image resolution, surpassing that of most earlier quantum imaging work.