Femtosecond laser-induced filamentation typically exhibits pronounced spectral broadening, featuring a bright central white core encircled by concentric colored rings that span from the ultraviolet to the visible range and extend into the infrared. While ionization, self-steepening and self-phase modulation are widely accepted as explanations for the white spot, the underlying physics of colored rings remain inadequately understood by current models, such as Cherenkov radiation and four-wave mixing. In this study, inspired by the observation of similar discrete colored rings produced by cascaded four-wave mixing (CFWM) of intersecting beams, we systematically investigated the relationship between the colored rings in the white-light supercontinuum and CFWM. The CFWM model accurately predicted the correlation between color and divergence angles, thereby enhancing our understanding of spectral broadening in filamentation and providing guidance for optimizing the conversion efficiency and configuration of multi-wavelength ultrashort optical pulses in both spatial and spectral domains.

The imperative to improve the remote detection efficiency of Lidar technology has motivated research on the directivity of backscattered signals. The nondirectional nature of typical fluorescence poses a significant challenge to remote single-sided detection based on fluorescence. Here, we demonstrate a highly directional amplified fluorescence confined by a self-waveguide induced by an air filament at a remote distance. The structure of the waveguide is similar to conventional optical waveguides and is proven to arise from the amplification of fluorescence inside the filament. New phenomena in this work indicate that the directivity could be further optimized to less than 7 degrees by simply extending the propagation distance of the filament. The backward detection efficiency could be improved by two orders of magnitude, compared to conventional isotropic fluorescence. This considerable advantage significantly boosts the detection sensitivity and extends the detection ranges in remote sensing applications.

A phase-retrieval-based 4-dimensional diagnostic method is proposed to resolve the spatial and temporal evolution of plasma in air induced by ultrafast laser. The plasma evolution dynamics (from generation to relaxation) were temporally resolved across several hundred picoseconds, spanning 3 orders of magnitude in measurable electron density (10 15 to 10 18 cm −3 ). The proposed method provides comprehensive, microscopic, and instantaneous insight into the underlying physical mechanisms of nonlinear phenomena induced by femtosecond filament.

Live cell sorting enables the acquisition of highly purified and functionally preserved populations for applications in disease diagnosis, stem cell research, and precision medicine. However, achieving high-efficiency and fully automated sorting remains challenging. Here, we present a real-time parallel AI holographic optical tweezer (PAIHOT) system that integrates YOLOv11n detection with Kalman filtering and class-matching for stable multi-target tracking and prediction in real time. Predicted trajectories guide the optical trap to the cell periphery, thereby reducing photodamage compared to conventional center-focused trapping. Experimental results demonstrated that PAIHOT achieves sorting purities exceeding 91% across multiple cell types, and the viability assays confirm intact morphology and strong growth activity. The PAIHOT enables highaccuracy, parallel, and low-damage cell sorting in dynamic microscopic environments, providing an effective and robust platform for intelligent, high-throughput single-cell research.

We numerically investigate an all-dielectric metasurface sensor based on an asymmetrically notched silicon nanodisks array for high-performance refractive index sensing via quasi-BIC excitation. By breaking in-plane rotational symmetry and gradually adjusting the asymmetry structure parameter, a tunable Fano resonance with flexible Q-factor engineered in the near-infrared region can be achieved. Under vertical illumination along the z-axis, the optimized high-Q factor metasurface configuration generates an extremely narrow resonance peak at 980 nm with calculated Q-factor reaching 9400. For ambient refractive indices ranging from 1.33 to 1.37, the sensor exhibits a sensitivity of 440.3 nm/RIU and a FOM of 4223 RIU⁻¹. With the same designed nanodisk unit by geometric parameter optimization, the Q-factor can be deliberately adjusted to 765 to enable the intensity-based sensing scheme achieving a sensitivity of 26.2 RIU⁻¹ at a fixed wavelength. Owing to its simple structure and dual- scheme sensing capability, the proposed all-dielectric metasurface offers a promising platform for applications in biosensing, environmental monitoring, and optical filtering.

High aspect ratio holes in nickel-based alloys have significant applications in the film cooling of aircraft turbine engines. The high inlet temperature (>2200 degrees C) of the next generation turbine engine imposes stringent requirements on the cooling efficiency of its hot components such that the commercial macro-hole cooling with cooling efficiency <= 60% cannot meet the requirements. Micro cooling holes with diameter of similar to 0.1 mm are proposed to generate up to 90% cooling efficiency. However, current processing techniques face challenges of inefficient debris removal and debris redeposition on the inner walls, making it difficult and inefficient to fabricate high aspect ratio holes with diameters <= 0.1 mm. In this work, an aerosol assisted laser spinning method is proposed to fabricate free tapered or reverse tapered holes with diameters <= 0.1 mm and aspect ratios >= 20 in nickel-based alloys. The aerosol modulates the laser intensity distribution and the hole's perforation time is reduced by 35.6%. This study provides a cost-effective drilling efficiency improvement method for fabricating high aspect ratio micro-holes in opaque materials with broad applicability, particularly in processing micro cooling holes in turbine engines.

Spatial-light computing requires rewritable, multilevel and persistent optical weights, but many implementations rely on volatile modulators or static power. Here we report a CMOS-imaged luminescent memristor array in which ferroelectric domain switching in Er/Yb-doped PMN-PT single crystals programs non-volatile photoluminescence (PL) states. Domain reconfiguration tunes the local crystal-field symmetry of lanthanide emitters, enabling 16 analogue levels, retention over 27 h, endurance beyond 105 cycles and microsecond-scale state programming with zero electrical standby power for state retention. An 8 × 8 array, addressed by a diffractive optical element and read by a proximal CMOS sensor, converts stored emissive states into a single-frame intensity map and achieves 94.02% pixel-wise state recognition using calibration-aware decoding. The array implements single-step optical linear weighting, while the same decoded weights support hybrid optical-electrical handwritten-digit inference approaching a 32-bit floating-point software baseline. These results establish a non-volatile, image-addressable emissive weight element for photonic computing. Spatial-light computing is limited by the lack of compact, non-volatile, rewritable analog devices. Wen et al. report a ferroelectric crystal that converts lanthanide emission into a rewritable, multilevel memory, allowing stored optical states to be read and used as persistent weights for neuromorphic computing.

Objective Narrowband multicycle terahertz (THz) pulses are indispensable for advancing applications in nonlinear optics, high-sensitivity spectroscopy, and THz-driven material control. Current optical methods for generating such pulses predominantly rely on lithium niobate (LN) crystals, with phase-matching techniques (e. g., tilted pulse fronts or subwavelength waveguides) used to achieve spectral narrowing. However, these techniques have inherent limitations owing to structural losses in conventional waveguide geometries, particularly in x-cut LN configurations. The alignment between the THz electric field and the spontaneous polarization of the crystal in such waveguides exacerbates propagation losses, resulting in spectral broadening and reduced coherence-critical barriers for applications requiring ultra-narrow bandwidths and extended wave trains. To address these issues, this study proposes a z-cut LN subwavelength waveguide design that uses the anisotropic properties of the crystal to minimize THz wave attenuation. In contrast to x-cut LN, the z-cut orientation inherently supports transverse magnetic (TM) mode propagation, where the THz electric field component along the longitudinal direction of the waveguide has less interaction with the ionic lattice of the crystal. This study is important owing to the urgent demand for high-coherence THz sources that are compatible with air propagation and can be integrated into compact systems in a scalable manner. By optimizing waveguide geometry and excitation dynamics, the study aims to establish a foundational framework for low-loss, narrowband THz generation, bridging the gap between theoretical phase-matching strategy and practical device implementation. This advancement is pivotal for enabling next-generation THz technologies in fields such as on-chip sensing, ultrafast spectroscopy, and coherent control of quantum materials. Methods The study uses a femtosecond laser-driven method to generate narrowband multicycle THz waves in a z-cut LN subwavelength waveguide (Fig. 1). A titanium-doped sapphire femtosecond laser (800 nm wavelength, 35 fs pulse duration, 500 Hz repetition rate) is used to laterally pump the waveguide. To optimize excitation efficiency, the laser beam is polarized parallel to the optical axis of the crystal and focused onto the waveguide edge using a cylindrical lens. The phase matching between the laser and THz waves is achieved using the waveguide geometry and the z-cut crystal orientation, which supports TM mode propagation with reduced losses. A THz photoconductive antenna, synchronized with the pump laser using a delay line, is used to detect the emitted THz waves. The system uses off-axis parabolic mirrors to collimate and focus THz radiation onto the antenna, coupled with a hemispherical silicon lens for enhanced signal collection. Pump-probe techniques and lock-in amplification are used to resolve the time-domain THz waveforms. In addition, phase-contrast imaging integrated with pump-probe measurements maps the spatiotemporal evolution of THz fields inside the waveguide. This involves frequency-doubling of probe beam to mitigate pump-induced noise, allowing for direct visualization of refractive index modulations caused by THz waves. The experimental validation compares z-cut and x-cut LN waveguides by examining spectral bandwidth, propagation modes, and loss mechanisms. Dispersion curves and mode profiles are derived from Maxwell equations, aligning theoretical predictions with measured TM-mode dominance in z-cut configurations. This methodology systematically links waveguide design and advanced detection techniques to achieve low-loss, narrowband THz generation (Fig. 2). Results and Discussions This study presents a novel method to produce narrowband multicycle THz waves using a z-cut LN subwavelength waveguide pumped by femtosecond lasers (Fig. 1). The z-cut LN waveguide design addresses the limitations of conventional x-cut LN waveguides, which limit spectral peak width to similar to 30 GHz owing to structural losses. The experimental results demonstrate a narrowband THz pulse with a spectral peak at 0.51 THz and a full width at half maximum (FWHM) of 15 GHz (Table 1). This enhancement is attributed to the TM-mode THz wave propagation in the z-cut waveguide, where the longitudinal electric field component aligns with the spontaneous polarization axis of the crystal, reducing lattice-induced losses and enabling longer wave trains. The study further uses phase-contrast imaging and pump-probe techniques to spatially and temporally resolve THz wave dynamics within the waveguide ( Fig. 5). In addition, dispersion analysis reveals that the generated THz waves exhibit TM0 mode characteristics, with experimental dispersion curves aligning well with theoretical predictions (Fig. 6). This study highlights the importance of crystal orientation and waveguide engineering in improving THz generation efficiency and spectral control. Conclusions This study presents z-cut LN subwavelength waveguides as a platform for producing narrowband multicycle THz pulses. Using the anisotropic properties of z-cut LN and optimizing phase matching through TM-mode propagation, the study addresses critical limitations of conventional x-cut waveguides, where structural losses and spectral broadening hinder high-coherence applications. The femtosecond laser-driven excitation in the z-cut configuration achieves a 15 GHz bandwidth at 0.51 THz, with a fivefold increase in frequency-to-bandwidth ratio. These advancements are owing to the suppressed interaction between the longitudinal THz electric field component and the ionic lattice of the crystal, which reduces propagation losses and increases wave train durations to 150 ps. The integration of pump-probe techniques, phase-contrast imaging, and dispersion analysis provides rigorous validation of the TM-mode dominance and phase-matching efficacy in z-cut waveguides. In contrast to broadband pulses from oblique laser incidence, the demonstrated narrowband THz waves propagate freely in air without requiring resonant microstructures, enhancing their practicality for real-world applications. This breakthrough addresses long-standing challenges in achieving scalable, low-loss THz sources compatible with compact photonic systems. By bridging material engineering with waveguide design, the study unlocks new opportunities in high-resolution spectroscopy, ultrafast material control, and on-chip terahertz devices.

We present a tunable Q-switched fiber laser based on a titanium carbide (TiC) optical modulator and a multimode interference filter (MMIF). By preparing the TiC optical modulator and inserting it into an erbium-doped fiber laser (EDFL), stable Q-switched operation at 1558 nm is observed at pump powers ranging from 50.6 to 178.2 mW. Simultaneously, the laser pulses exhibit the repetition frequency of 11.49-36 kHz and the pulse width of 28-2.6 & micro;s. When the pump power was 84.6 mW, the laser pulses display the signal-to-noise ratio (SNR) of 51 dB. Furthermore, the home-made MMIF is constructed in a single-mode fiber (SMF)-multimode fiber (MMF)-SMF configuration. By mechanically bending the MMIF, it is observed that the transmission spectrum of the MMIF exhibits periodic variations. Over one period, the peak wavelength of the MMIF transmission spectrum exhibits a blue shift. When inserting the MMIF into the Q-switched EDFL, a tunable Q-switched EDFL with a tuning range of 7.4 nm was realized by altering the MMIF. The tuning range consists of three discontinuous tuning windows. This paper presents the all-fiber integrated pulsed light source, which can be applied in areas such as optical sensing. (c) 2026 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Designing nonlinear optical (NLO) materials that integrate high stability with broad tunability is essential for photonic technologies such as laser protection and dynamic light control. Herein, we utilize photoactive ligand coumarin to deliver photogenerated electrons and stabilize the reduced state in the vanadium-based nanocluster (C3), significantly enhancing its nonlinear refraction and prolonging the response stability. Density functional theory reveals that coumarin narrows the band gap (from 0.43 to 0.40 eV), promotes charge transfer, and stabilizes reduced vanadium centers (the average Mulliken charge decreases from 1.127 to 1.112), enabling C3 to retain more than 85% of original NLO efficiency after 24 h. Moreover, C3 exhibits self-initiated polymerization behavior, forming solid-state films that sustain strong nonlinearity for hours and allow multiple UV reactivation cycles. Therefore, this work provides a general design strategy for achieving highly tunable and robust NLO materials by leveraging photoactive organic ligands to transfer electrons and stabilize reduced electronic states in metal oxide nanoclusters. (c) 2026 Chinese Laser Press

Clinical refractive surgeries for myopia correction generally entail stromal tissue removal with risks of postoperative complications. NIR femtosecond laser-induced corneal two-photon collagen cross-linking (two-photon CXL) through photochemical effects can lead to localized refractive index (RI) changes in the cornea, promising for non-ablative and non-incisional visual correction. However, previous studies mainly focused on hydrogels and animal corneal tissues, adopting a diffraction grating method that is difficult for biological tissue. Here we systematically investigate femtosecond laser-induced RI changes in human corneal tissue, demonstrate two-photon excitation of riboflavin leading to cross-linking, and employ direct interferometry to quantify RI changes. The maximum RI change is 3.80 ± 0.45 × 10-3 in collagen hydrogel and 5.14 ± 0.75 × 10-3 in corneal tissue. These findings illustrate that RI engineering by femtosecond laser two-photon CXL is promising for noninvasive refractive surgery.

Two-dimensional excitonic devices are of great potential to overcome the dilemma of response time and integration in current electronic and/or photonic systems, where dynamically controlling the spatiotemporal dynamics of exciton flux is a cornerstone. Although tip-induced strain engineering and surface acoustic waves (SAWs) have been proposed, the complex accessorial configurations severely limit the applications in integrated devices. Here, we systematically investigate phase transition engineering of vanadium dioxide (VO2) for exciton dynamics in an atomically thin semiconductor. Temperature-dependent photoluminescence (PL) spectra demonstrate that PL reaches a maximum at the phase transition temperature T c (340 K), due to the increase in free carrier density during the insulator-to-metal transition. The thermal hysteresis loop is first observed from PL spectra due to the latent heat in the phase transition. The increased free carrier density during the VO2 phase transition can dynamically modulate the exciton diffusion coefficient, where the enhanced charged excitons (trions) near the insulator-metal transition temperature promote the exciton diffusion coefficient. The hexagonal boron nitride (hBN) intercalation mitigates the VO2-induced negative effects through dielectric screening and interfacial defect reduction while preserving the dynamic phase transition modulation capability in the PL spectra and yielding a more than doubled enhancement of the exciton diffusion coefficient. These findings highlight the importance of phase transition engineering for two-dimensional (2D) exciton-based devices and lay a foundation for the development of functional excitonic devices.

Terahertz (THz) nonlinear optics offer powerful tools to investigate and manipulate electronic dynamics in condensed matter. Confining high-peak-power THz pulses within near field can effectively generates extremely localized electromagnetic fields in spatio-temporal, enabling to precisely explore and control carrier transient dynamics from THz nonlinearity perspective. However, the combination of the high peak power THz pulses and the near-field optic techniques remains challenging due to the incompatibility between low repetition THz pulses and typical near-field demodulation schemes. Here, we construct high peak power THz scattering scanning near-field microscopy (THz s-SNOM) by combining THz pulses emitted from two-color femtosecond laser filaments with a tapping mode atomic force microscopy (AFM) and explore efficient THz third harmonics generation (THG) from the Cd3As2 film in nanoscale. The power-law dependence of the THz harmonics and theoretical calculation reveals a convincing third harmonic generation that is attributed to the nonequilibrium intraband dynamics driven by the strong THz pulses. Especially, the nanoscopic near-field THz third harmonic imaging with resolution of 200 nm (λ/3000) of 3D Dirac semimetal are demonstrated. The high peak power THz s-SNOM can provide a great platform for exploring and manipulating the nonlinear physics, carrier dynamics and quantum coherent phenomena driven by the localized THz field with nanoscale resolution, thereby guiding the development of the integrated high-performance nonlinear photonic devices.

In-sensor computing paradigm holds the promise of realizing rapid and low-power signal processing. Constructing crossmodal in-sensor computing systems to emulate human sensory and recognition capabilities has been a persistent pursuit for developing humanoid robotics. Here, an artificial mechano-optical synapse is reported to implement in-sensor dynamic computing with visual-tactile perception. By employing mechanoluminescence (ML) material, direct conversion of the mechanical signals into light emission is achieved and the light is transported to an adjacent photostimulated luminescence (PSL) layer without pre- and post-irradiation. The PSL layer acts as a photon reservoir as well as a processing unit for achieving in-memory computing. The approach based on ML coupled with PSL material is different from traditional circuit-constrained methods, enabling remote operation and easy accessibility. Individual and synergistic plasticity are elaborately investigated under force and light pulses, including paired-pulse facilitation, learning behavior, and short-term and long-term memory. A multisensory neural network is built for processing the obtained handwritten patterns with a tablet consisting of the device, achieving a recognition accuracy of up to 92.5%. Moreover, material identification has been explored based on visual-tactile sensing, with an accuracy rate of 98.6%. This work provides a promising strategy to construct in-sensor computing systems with crossmodal integration and recognition.

Objective Ultrafast laser filamentation finds applications in remote sensing, lightning control, free-space communications, air lasing, terahertz (THz) wave generation, and pulse compression, owing to its unique characteristics. The spatial distributions of intensity and plasma density inside the filaments critically determine the key properties of filament-induced emissions (e.g., THz waves and supercontinuum sources), including spatial profile, polarization, divergence, and conversion efficiency. Consequently, beam shaping techniques, such as Gaussian beam, super-Gaussian beam, flat-top beam, Bessel beam, and Airy beam, are employed to control the spatial distributions of filaments as well as their emissions. Practical implementations result from beam perturbations caused by optical aberrations, thermal distortions, diffraction, turbulence, and nonlinear effects. These deviations from ideal beam profiles induce asymmetric intensity/plasma distributions within filaments, detrimentally affecting secondary processes (e.g., THz emission, supercontinuum generation, and air lasing). Quantifying these non-ideal effects is thus essential for optimizing applications. This work specifically investigates how the asymmetric laser beam profile governs filament asymmetry and what is the impact on the supercontinuum profile. This work provides fundamental insights for controlling filament-derived radiation sources. Methods The plasma distribution inside femtosecond laser filaments is characterized experimentally by a pump-probe plasma diffraction technique. A second harmonic laser beam at 400 nm is chosen as the probe beam to propagate perpendicularly through the plasma channel. Refractive index modulation induced by plasma imprints a spatially varying phase shift onto the probe wavefront. This phase modulation is converted into a measurable diffraction pattern. To explain and prove the experimental results, numerical simulations based on the nonlinear propagation equation and Fresnel diffraction theory are performed. Results and Discussions The experimental and simulation results give contributions to the generation mechanisms, the modulation methods, and the impact on supercontinuum generation with spatial asymmetry during femtosecond laser filamentation. Experimental measurements reveal that non-ideal beam profiles fundamentally alter filamentation dynamics. Plasma diffraction patterns demonstrate that input beam asymmetry induces characteristic curved diffraction fringes (Fig. 2), directly mapping asymmetric plasma distributions. Critically, this asymmetry is focusing-condition dependent. High-numerical aperture (NA) focusing configurations show obvious transverse density contrast in filaments [Fig. 4(a)], while low-NA (1/2000) configurations suppress asymmetry. Besides, beam displacement at the focusing lens provides an active control on the filament asymmetry. By this method, the spatial profile of supercontinuum generated from filaments is effectively controlled. Conclusions Imperfections in laser beam spatial profiles represent a pervasive challenge in practical applications. We demonstrate that asymmetries in the laser mode profile induce corresponding asymmetries in the laser intensity distribution and plasma density distribution inside the filament. Furthermore, the asymmetry degree is modulated by external focusing conditions, exhibiting significant attenuation under low NA configurations. Additionally, by actively manipulating the asymmetric distribution of the filament, the spatial distribution of supercontinuum is controlled. This research elucidates the fundamental mechanisms governing asymmetric spatial distributions in femtosecond laser filamentation, providing crucial theoretical foundations for applications reliant on filament-derived radiation, such as supercontinuum sources and terahertz waves.

Memristors enable non-volatile memory and neuromorphic computing. Optical memristors are the fundamental element for programmable photonic integrated circuits due to their high-bandwidth computing, low crosstalk, and minimal power consumption. Here, an optical memristor enabled by a non-volatile electro-optic (EO) effect, where refractive index modulation under zero field is realized by deliberate control of domain alignment in the ferroelectric material Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) is proposed. The non-volatile EO memristor is designed exclusively for the modulation of the optical phase without degrading the optical transparency, and it allows the support for deterministic and repeated non-volatile multilevel EO states. A non-volatile tunable waveplate composed of the optical memrisor for free-space optics, which allows for deterministic multilevel, and non-volatile phase shifts from 0 to π /2 is presented. The state switching rate of the memristor is less than 100 ms, with a switching energy consumption of 234 nJ, and the states can be retained for up to 12 h without requiring static power consumption. These results demonstrate a novel approach to fully realizing non-volatile optical memristors, where only optical phase modulation is involved, providing unprecedented opportunities for the development of new ferroelectric memristors.

Among the terahertz (THz) sources, a two-color femtosecond filament in gases provides the coherent THz emission with the most broadband spectrum, which spans up to several tens of THz. Optical to terahertz conversion efficiency in the gas-based plasma reaches ~0.01% for the near infrared (800+400 nm) or up to 1% for the mid-infrared pump [1]. By positively chirping the initial pulse, one can increase the optical to THz conversion efficiency by an order of magnitude [2]. The THz yield depends strongly on the relative phase between the fundamental and the 2nd harmonic radiation. Recently it was found that the relationship between THz pulse energy and chirp changes with variations in the specific phase difference between the first and second harmonics, and that the maximum THz energy might be attained not only for positively, but also for the negatively chirped pulse [3].

A lens-free terahertz computed tomography method based on metamaterial waveguide (meta-waveguide) is proposed. In this method, the meta-waveguide replaces the traditional terahertz lens or mirror. It not only inherits the low-loss transmission performance of the waveguide but also breaks through the diffraction limit and achieves subwavelength focusing. Its focusing distance is greater than the Rayleigh length, which is helpful for Radon scanning and tomography imaging. The focusing and transmission characteristics of terahertz in meta-waveguide are analyzed, and the principle of meta-waveguide-based computational tomography system is presented. Then, a 3D printing and copper plating method was proposed for processing the meta-waveguides. Finally, a 0.1 THz Radon tomography scanning system was established. High quality terahertz images with a resolution of 1/3 of the wavelength were obtained, and the three-dimensional image of biological tissue (artificial blood vessel) was acquired.