Modeling reflectance for finite source-detector geometries typically requires Monte Carlo simulations with explicit illumination and collection areas. We present a distance-weighted formulation that computes reflectance...Modeling reflectance for finite source-detector geometries typically requires Monte Carlo simulations with explicit illumination and collection areas. We present a distance-weighted formulation that computes reflectance for arbitrary overlapping, concentric, and non-overlapping source-detector geometries from a single, localized (quasi-pencil-beam) Monte Carlo simulation. Reflectance is expressed as an integral of the radial reflectance profile weighted by the distribution of source-detector separations. The method incorporates finite launch and detection numerical apertures and extends to non-uniform illumination and detection through an appropriate effective distance distribution. Monte Carlo validation against full source-detector simulations shows agreement in both reflectance and pathlength distributions for geometries relevant to fiber-based reflectance spectroscopy. This provides a general and efficient framework for laterally homogeneous media.
External electrical fields (EFs) provide a unique strategy to manipulate fluid deformations independently of thermal parameters. This offers a unique opportunity in laser processes involving melting, where melt pool resp...External electrical fields (EFs) provide a unique strategy to manipulate fluid deformations independently of thermal parameters. This offers a unique opportunity in laser processes involving melting, where melt pool responses can be complex. Here, we explore the effects of non-contact EFs during laser processing of stainless steel. Metal powder is locally melted and resolidified under a constant laser energy input in the presence of various EFs. Both constant and time-varying EFs induce significant changes upon resolidification, transforming naturally spherical droplets into anisotropic oblate melt geometries aligned with the applied field. Calculations indicate EFs alter surface tension, leading to changes in the wetting behavior of the melt. This fundamental investigation of non-contact EFs in laser processing puts forward an approach that enables control over fluid responses independently of laser parameters.
Laser active polarization imaging is susceptible to coherent speckle noise, which severely degrades both image quality and the accuracy of polarization parameter estimation. Existing polarimetric denoising methods, predo...Laser active polarization imaging is susceptible to coherent speckle noise, which severely degrades both image quality and the accuracy of polarization parameter estimation. Existing polarimetric denoising methods, predominantly designed for additive noise models, struggle to handle speckle noise due to its complex statistical characteristics while failing to fully exploit the structural correlations among multi-channel polarization images. To address these limitations, this study proposes a polarimetric speckle suppression network named PoDeFormer, which achieves effective speckle removal by establishing the intrinsic connection between incoherent illumination and coherent speckle in laser active polarization imaging. Experimental results demonstrate that the network not only effectively removes speckle noise while preserving polarization information integrity but also enables fast inference with minimal computational overhead, providing an efficient and reliable solution for real-time denoising in laser active polarization imaging applications.
A high-power 1-MHz dual-crystal Yb:CALGO femtosecond regenerative amplifier (RA) is demonstrated with an average output power of 55 W, while featuring a carefully selected central wavelength of 1048 nm, whose third harmo...A high-power 1-MHz dual-crystal Yb:CALGO femtosecond regenerative amplifier (RA) is demonstrated with an average output power of 55 W, while featuring a carefully selected central wavelength of 1048 nm, whose third harmonic wave of 349 nm is expected to enable high-efficiency 10.6-eV vacuum ultraviolet (VUV) source generation. Here, spatial chirp is intentionally introduced in the Offner stretcher and employed for shaping the seed spectrum to compensate for gain narrowing and spectral blue-shift during regenerative amplification. After compression, 51 W output with a pulse duration of 146 fs was obtained, with beam quality factors of M = 1.16 and M = 1.16. Furthermore, 349-nm ultraviolet radiation with an output power of 3.1 W was obtained with two pieces of cascaded beta barium borate (BBO) crystals.
We demonstrate a simplified single longitudinal mode (SLM) L‑band erbium‑doped fiber laser using an active fiber loop mirror (AFLM). It requires no separate saturable absorber or circulator. Stable SLM operation is achie...We demonstrate a simplified single longitudinal mode (SLM) L‑band erbium‑doped fiber laser using an active fiber loop mirror (AFLM). It requires no separate saturable absorber or circulator. Stable SLM operation is achieved with an output power of 3-4 mW and a wavelength drift <1 pm over 10 minutes. Reflectance measurements show that an absorption dynamic grating (ADG) in the unpumped fiber section provides narrowband selection, while a gain dynamic grating (GDG) in the pumped section reduces reflection contrast from 20% to 3% at high pump power. Nonetheless, the ADG remains strong enough to prevent mode hopping. The design offers a compact, low‑cost L‑band SLM laser.
A 4H-SiC n-p-n floating-base phototransistor (FB-PT) achieving ultra-high responsivity via a punch-through induced barrier lowering (PT-IBL) mechanism is reported. By engineering the base region to operate near the struc...A 4H-SiC n-p-n floating-base phototransistor (FB-PT) achieving ultra-high responsivity via a punch-through induced barrier lowering (PT-IBL) mechanism is reported. By engineering the base region to operate near the structural punch-through state, the emitter-base barrier becomes highly sensitive to photogenerated hole accumulation. The device exhibits an ultra-high peak responsivity of 9.8 × 10 A/W at 272 nm under 9 V bias. Based on the high spatial response uniformity observed at 7 V, the FB-PT demonstrates an optimized balance of performance, yielding a specific detectivity (*) of ~3.5 × 10 Jones, a noise equivalent power () of ~10.8 fW, a responsivity of 125 A/W, and rise/fall times of ~5.1/9.4 ms. Furthermore, a single-pixel imaging system using this FB-PT reconstructs high-fidelity patterns under a low light intensity of ~1 μW/cm. These results quantify the potential of the PT-IBL mechanism for sensitive UV sensing and integrated optoelectronics.
We present a long-range, multi-point spectroscopic gas-sensing method that incorporates coherence multiplexing into optical frequency-modulated continuous-wave (FMCW) spectroscopy to significantly increase the sensing di...We present a long-range, multi-point spectroscopic gas-sensing method that incorporates coherence multiplexing into optical frequency-modulated continuous-wave (FMCW) spectroscopy to significantly increase the sensing distance. In this method, the sensing region is segmented to suppress the accumulation of phase noise along the optical path, and the optical delay of the reference is accordingly adjusted segment by segment to achieve optimal match of optical coherence. As a proof-of-concept, multi-point acetylene gas sensing is experimentally demonstrated, achieving a minimum detectable concentration of 0.94 ppm and a sensing spatial resolution of 0.46 m over a distance of 11 km, extending the sensing range by a factor of 60. Provided a sufficient optical power budget is maintained, the system can potentially multiplex thousands of sensors. The proposed coherence-multiplexed FMCW spectroscopy relaxes requirements on laser coherence, detection bandwidth, and computing power, offering a low-cost and high-capacity route to distributed gas monitoring in large-scale, long-distance scenarios.
We demonstrate a 4-channel O-band (de)multiplexer based on silicon nitride (SiN) Mach-Zehnder interferometer (MZI) lattice filters. By utilizing geometry-dependent modal behavior to tailor the effective thermo-optic coef...We demonstrate a 4-channel O-band (de)multiplexer based on silicon nitride (SiN) Mach-Zehnder interferometer (MZI) lattice filters. By utilizing geometry-dependent modal behavior to tailor the effective thermo-optic coefficient (d/d) of the SiN waveguides, near-athermal operation is achieved against global temperature fluctuations. The device architecture utilizes Hermite-curve-assisted folded arms to ensure a compact footprint while maintaining high sensitivity to local micro-heaters for power-efficient channel alignment. Fabricated on an 8-inch wafer with 300-nm-thick SiN, the device exhibits a significantly suppressed temperature sensitivity of ~2 pm/K. The integrated phase shifters achieve a low π-phase-shift power of ~30 mW. Comparative analysis with state-of-the-art SiN platforms highlights the superior performance of this design in both passive thermal stability and active tuning efficiency.
Metasurfaces resolve limited signal-to-noise ratio (SNR) and radio frequency (RF) inhomogeneity bottlenecks in magnetic resonance imaging (MRI). However, strong unit-cell near-field coupling creates an "ill-posed"' desig...Metasurfaces resolve limited signal-to-noise ratio (SNR) and radio frequency (RF) inhomogeneity bottlenecks in magnetic resonance imaging (MRI). However, strong unit-cell near-field coupling creates an "ill-posed"' design problem, where conventional optimization struggles with computation costs and non-unique mappings. We propose a physics-constrained bidirectional deep learning framework for MRI metasurfaces. A Spectral-Feature U-Net surrogate model substitutes time-consuming simulations. To address multi-valued mapping in inverse design, a tandem training strategy with physics-consistency constraints guides a residual multi-layer perceptron (Res-MLP) toward physically equivalent solutions. In simulations incorporating a human arm phantom, an AI-designed metasurface achieved precise 63.8 MHz resonance and excellent field homogeneity, keeping specific absorption rate (SAR) within safety limits. This establishes a robust "AI for Science" toolchain for automated, patient-adaptive MRI hardware design.
Ultraviolet (UV) imaging can reveal structural flaws, fluorescent markers, and characteristic signals generated by material changes that are difficult to detect in visible-light imaging and has been applied in numerous f...Ultraviolet (UV) imaging can reveal structural flaws, fluorescent markers, and characteristic signals generated by material changes that are difficult to detect in visible-light imaging and has been applied in numerous fields. However, in traditional UV imaging, it is challenging to simultaneously acquire reflection/transmission and UV-excited fluorescence imaging, often requiring additional optical filters to eliminate interference bands. Here, we demonstrate a dual-mode UV lensless imaging method based on diffuser speckle modulation, which enables direct reconstruction of both reflection/transmission and fluorescence images from a single-shot measurement. Compared with conventional methods, our scheme eliminates the need for optical lenses and filters, enabling an ultra-compact lensless system. This approach can be further integrated with other image post-processing operations or general computer vision tasks for the development of task-oriented intelligent UV cameras.
This article presents a method for direct estimation of modal wavefront coefficients from speckle images obtained using a thin diffuser. Zernike coefficients are recovered from intensity differences between reference and...This article presents a method for direct estimation of modal wavefront coefficients from speckle images obtained using a thin diffuser. Zernike coefficients are recovered from intensity differences between reference and distorted speckle patterns using a least-squares formulation derived from a first-order Taylor expansion. Simulations demonstrate accurate reconstruction across a range of aberrations and detector noise levels. Compared to the Demon algorithm, the proposed method shows improved performance for small aberrations and under noisy conditions, while Demon performs better at large amplitudes. Experimental validation demonstrates good agreement with Shack-Hartmann measurements, with residual RMS errors consistent with experimental uncertainty.
A widely utilized optical diagnostic, focused laser differential interferometry (FLDI), generates pseudo-point-like measurements with suppressed off-axis signals. However, prior studies reveal that off-axis disturbances...A widely utilized optical diagnostic, focused laser differential interferometry (FLDI), generates pseudo-point-like measurements with suppressed off-axis signals. However, prior studies reveal that off-axis disturbances with longer wavelengths remain integrated into the final FLDI measurement, making conversion of the measurement to true density units challenging. To overcome this limitation, intersectional FLDI (iFLDI) is proposed, utilizing two or more identical FLDIs that intersect at the region of interest. The coherence between the FLDIs is leveraged to identify and remove the contaminating off-axis noise. This novel, to the best of our knowledge, improvement is computationally tested with a high-fidelity simulation of a hypersonic turbulent flow with and without an inserted sinusoid. Two filtering methods are used to reconstruct the final signal. iFLDI is shown to approach an idealized point measurement in both spectral shape and amplitude relative to a single FLDI measurement. Crucially, the final, improved spectrum produces a quantitative measurement of the density change without the drawbacks of previously proposed calibration techniques.
A fiber FI/FO device based on a micro-lens array (MLA) is proposed in which the compact fiber bundle method is combined with 3D printing, enabling low-loss and high-robustness fiber interconnection. Single-mode fibers (S...A fiber FI/FO device based on a micro-lens array (MLA) is proposed in which the compact fiber bundle method is combined with 3D printing, enabling low-loss and high-robustness fiber interconnection. Single-mode fibers (SMFs) are etched by a chemical process and assembled into a fiber array matched to a multi-core fiber (MCF), while a polymer MLA is directly printed on the MCF end facet using a Nanoscribe 3D printing system. The MLA reduces the alignment sensitivity of the fiber array and improves the tolerance of the conventional fiber bundle method, thereby effectively reducing the coupling loss. A seven-core MLA FI/FO device is fabricated as a proof of concept. Benefiting from the MLA's effective beam control capability, the experimental results show that the insertion loss is significantly reduced under different alignment conditions. Under poor alignment conditions, the insertion loss of the device without lenses is about 1.62 dB and is reduced to 0.97 dB after introducing the MLA, corresponding to an improvement of 0.65 dB and demonstrating strong robustness against misalignment. Under good alignment conditions, the insertion loss is further reduced from about 0.77 dB to 0.48 dB, indicating both high tolerance and low-loss potential of the MLA-based FI/FO device. Further measurements show that the average inter-channel crosstalk remains below -60 dB over the entire C + L band, confirming the low-crosstalk performance of the proposed MLA FI/FO device.
Particle tracking methods are essential tools for probing the structure, dynamics, and interactions in colloidal systems. However, conventional methods often introduce systematic bias when particle images overlap. Image...Particle tracking methods are essential tools for probing the structure, dynamics, and interactions in colloidal systems. However, conventional methods often introduce systematic bias when particle images overlap. Image reconstruction algorithms can overcome these limitations, but they typically cannot handle in-situ changes in size and morphology-crucial aspects for stimuli-responsive colloids such as thermoresponsive microgels. Here, we introduce an adaptive full-image reconstruction method for radially symmetric particles in the micron-to-submicron size range that iteratively learns particle size and optical contrast directly from microscopy images, enabling simultaneous extraction of precise positions and morphologies. We apply this method to hybrid microgels loaded with gold nanoparticles, obtaining their position and shape.
Prism-coupled layered structures, including surface plasmon resonance (SPR) sensors and resonant mirror (RM) sensors, have been widely used in refractive index sensing. However, the interference-based signal detection of...Prism-coupled layered structures, including surface plasmon resonance (SPR) sensors and resonant mirror (RM) sensors, have been widely used in refractive index sensing. However, the interference-based signal detection of RM is sophisticated, and the low quality factor of the SPR mode limits sensing performance. In this work, an absorptive RM with independently tunable radiative and absorptive losses is proposed and theoretically investigated. By controlling the buffer layer thickness and waveguide extinction coefficient separately, the radiative quality factor () and absorptive quality factor () can be adjusted without crosstalk. When and are matched at the critical coupling condition, perfect absorption with ultra-narrow bandwidth is achieved. With a simple layer stack and compatibility with existing prism-coupled schemes, the proposed absorptive RM may offer a promising platform for label-free sensing.
Developing structurally simple, low-cost, and solution-processable white organic light-emitting diodes (WOLEDs) with a high color rendering index remains a challenge. Herein, a dye-free WOLED is developed based on a nove...Developing structurally simple, low-cost, and solution-processable white organic light-emitting diodes (WOLEDs) with a high color rendering index remains a challenge. Herein, a dye-free WOLED is developed based on a novel, to the best of our knowledge, polymer-small-molecule system constructed of poly(N-vinylcarbazole) (PVK) and 2-(9,9'-spirobi[fluoren]-3-yl)-4,6-diphenyl-1,3,5-triazine (SF3-TRZ). The device exhibits high-quality white electroluminescence originating from complementary emissions of the bluish-green PVK: SF3-TRZ exciplex and the electromer of SF3-TRZ. By further inserting a 4,4'-bis(9-carbazolyl)-2,2'-dimethylbiphenyl (CDBP) layer into the emission layer, a deep-blue CDBP/SF3-TRZ interfacial exciplex is formed to generate additional reverse intersystem crossing (RISC) channels, which further improve the performance of WOLED. Consequently, the optimized WOLED achieves broadband white emission with CIE coordinates of (0.32, 0.33) at 8 V and a high color rendering index (CRI) of 93. It delivers peak current and power efficiencies of 8.32 cd/A and 7.70 lm/W, respectively. This work paves the way for high-quality WOLED with simple architecture and low-cost fabrication.
Most existing lithography alignment methods adopt multi-wavelength light sources and off-axis illumination technologies. In practical lithography alignment scenarios, alignment marks are generally located in the wafer sc...Most existing lithography alignment methods adopt multi-wavelength light sources and off-axis illumination technologies. In practical lithography alignment scenarios, alignment marks are generally located in the wafer scribe lane, and their positions vary with the chip layout. Nevertheless, conventional off-axis illumination schemes are incapable of fixed-point illumination for alignment marks and coordinated regulation of light source wavelength and illumination incident angle. To address the above limitations, this paper proposes a frequency-domain enhanced spatial multi-position moiré fringe alignment method. The proposed method enables the modulation of illumination wavelength and incident angle at any position within the field of view of 7430 × 8830 μm, with an operating wavelength ranging from 532 nm to 635 nm. The measurement repeatability 3 value is less than 1 nm at arbitrary detection positions.
In this paper, a novel trace gas sensor based on on-off-beam differential resonance quartz-enhanced photoacoustic spectroscopy (ODR-QEPAS) is proposed. Relying on the differential characteristics of the acoustic resonanc...In this paper, a novel trace gas sensor based on on-off-beam differential resonance quartz-enhanced photoacoustic spectroscopy (ODR-QEPAS) is proposed. Relying on the differential characteristics of the acoustic resonance tube and integrating the advantages of two classic optical configurations (on-beam and off-beam) simultaneously, this structure realizes dual resonant enhancement of the photoacoustic signal. The finite element analysis (FEA) method was adopted to calculate the acoustic field distribution, which provides solid numerical support for the experimental investigation. Acetylene (CH) was selected as the target analyte to characterize the sensor performance, and the geometric parameters of the differential resonance tube were optimized. Under identical experimental conditions, the proposed ODR-QEPAS system outperforms the traditional bare QTF-based system, yielding an 18.92-fold increase in 2 signal amplitude, a 36.8% reduction in noise floor, and a 29.61-fold improvement in signal-to-noise ratio (SNR).
Polarization-resolved metasurfaces offer a compact platform for simultaneous control of wavefront and polarization; however, the role of aperture-level multiplexing in device performance remains largely unexplored. Here,...Polarization-resolved metasurfaces offer a compact platform for simultaneous control of wavefront and polarization; however, the role of aperture-level multiplexing in device performance remains largely unexplored. Here, we design and experimentally demonstrate two polarization-resolved multifocal metalenses based on plasmonic quarter-wave plates: a segmented metasurface and an interleaved metasurface. Under circularly polarized illumination, both devices generate four focal spots with independently prescribed linear polarization states, enabling simultaneous circular-to-linear polarization conversion and multifocal phase modulation. The two layouts are experimentally characterized and compared in terms of polarization-resolved focal-field distributions, angle-of-linear-polarization errors, and degree of linear polarization over a broadband wavelength range. These results provide practical guidelines for advanced polarization shaping and integrated flat photonic devices.
Electro-optic comb-based two-point optical frequency division (eOFD) provides a robust architecture for generating low-phase-noise microwave signals by transferring the relative frequency stability of a dual-wavelength l...Electro-optic comb-based two-point optical frequency division (eOFD) provides a robust architecture for generating low-phase-noise microwave signals by transferring the relative frequency stability of a dual-wavelength laser. However, this transfer process introduces residual phase noise that limits the achievable performance. Here, we show that electro-optic comb generation redistributes optical power while preserving the noise floor, leading to increased relative intensity noise (RIN) on individual comb lines. This RIN is converted into amplitude noise of the intermediate-frequency (IF) signal during heterodyne photodetection and is subsequently converted into microwave phase noise via amplitude-to-phase (AM-PM) conversion in the mixer. To suppress this effect, we employ a saturated RF amplifier after photodetection to compress amplitude fluctuations. A 12 dB reduction of the microwave phase noise is achieved, reaching -140 dBc/Hz at a 10 kHz offset frequency. This work identifies the dominant role of RIN-induced AM-PM conversion in limiting the phase noise of eOFD systems and provides a targeted strategy to suppress this effect.