We report a high-average-power picosecond source based on a four-stage, 888 nm in-band-pumped bulk Nd:YVO4 master-oscillator power amplifier and cascaded LBO conversion. Orthogonal c-axis amplifier cells delivered 1056 W at 1064 nm with 10.7 ps pulses. Walk-off-reversed dual-crystal second-harmonic generation produced 720 W at 532 nm with 68.6% conversion efficiency, whereas sum-frequency generation in ultra-low-absorption LBO yielded 329.3 W at 355 nm with 41.1% efficiency. The green and ultraviolet outputs exhibited RMS power fluctuations of 0.82% over 18 hours and 0.48% over 13 hours, respectively. The corrected beam quality was M[2] < 1.2 at 500 W green and 250 W ultraviolet output, respectively. To our knowledge, these average powers are the highest reported to date for bulk solid-state picosecond frequency-conversion architectures.

Ultrafast laser extreme structuring strategies provide an important capability of advancing nanoscale surface patterning by progressively exploiting near fields. These fields can be shaped in turn by the evolving surface structures, adapting to a dynamic topography. However, tracking the transition from an initial localized nanovoid to oriented nanotrenches with increasing pulse accumulation is essential to understanding the underlying physical processes. Here, we observe and clarify the stagewise evolution of nanopatterns on 4H-SiC by independently varying single-pulse energy and pulse number. Experiments varying the polarization of subsequent laser pulses show that initially isotropic nanovoids evolve into anisotropic nanotrenches elongated perpendicular to the subsequent pulse polarization. 3D finite-difference time-domain (FDTD) simulations based on representative experimental morphologies show that preformed structures redistribute the local electric field under subsequent irradiation. The simulated field distributions are consistent with the morphological features observed at later stages, supporting a stagewise structural feedback pathway.

In this Letter, we demonstrate that employing the Lens Aperture as a Knife-Edge (LAKE) with two identical LEDs has the distinct advantage of obtaining Schlieren images along two cutoff orientations. It is possible to control LED brightness to obtain a desirable weighted sum of both horizontal and vertical Schlieren cutoff images on each camera frame. Powering the LED sources by an affordable and programmable Arduino board enables a rapid switch between the horizontal and vertical Schlieren cutoffs that is exactly synced to the camera frames, resulting in a crosstalk-free Schlieren image sequence. Furthermore, with a little postprocessing, this monochrome image series can be easily transformed into a colorful sequence of bidirectional Schlieren images.

We demonstrate a Kerr-lens mode-locked (KLM) room-temperature Ti:sapphire laser achieving an average power exceeding 10 W in a single transverse mode with a slope efficiency of 35%. The laser operates at a repetition rate of 73.8 MHz, delivering sub-100-fs pulses with a maximum single-pulse energy of 160 nJ. Owing to excellent thermal management, the laser maintains long-term operation with a root-mean-square (RMS) power fluctuation of 1.08% at a power of 10.3 W over 6 hours. To the best of our knowledge, this represents the highest average power ever reported from a femtosecond Ti:sapphire mode-locked oscillator.

The free spectral range (FSR) is a key parameter in the design of optical resonators. However, material dispersion can cause nonuniform FSR variations across a broad wavelength range. To address this drawback, this study proposes a high-precision FSR measurement method that combines an electro-optic modulator with an orthogonal Mach-Zehnder interferometer (MZI). A tunable laser is electro-optically modulated to generate equally spaced sidebands, yielding stable frequency markers. Subsequently, the markers are combined with the unwrapped instantaneous phases obtained from the MZI to determine high-precision FSR. Using a fiber ring resonator as a representative example, the FSR varied by ~51.4 kHz over an 82.4-nm wavelength span. The measured FSR was used as a frequency-interval reference, together with the known absolute wavelength of the R9 line, to determine the center wavelengths of H[13]C[14]N gas absorption lines. As a result, an absolute measurement accuracy better than 0.24 pm was achieved, demonstrating the method's high precision and reliability. Thus, the proposed method enables high-precision characterization of optical resonator parameters across a wide spectral range and offers a practical approach to precision spectroscopy.

Single-ended vibration localization based on frequency-shifted optical delay lines avoids the time synchronization required by dual-ended schemes but requires costly narrow-linewidth lasers. To overcome this limitation, we introduce a transmitter-side matched-delay local oscillator (MD-LO) for the sensing unit. The MD-LO matches the sensing-link length and the delay paths between frequency-shifted components, which can tolerate laser phase noise through self-coherent detection. With sensing aided by the MD-LO, vibration detection down to 10 Hz under a 3-MHz-linewidth distributed-feedback (DFB) laser is achieved, and single-ended distributed vibration localization over a 25.2-km weakly coupled four-core fiber is demonstrated. As an illustrative example of integrated sensing and communication (ISAC), the sensing carrier also serves as the local oscillator for self-coherent communication, achieving 3 × 448 Gb/s net transmission over the remaining three cores.

Transmission matrices are essential for achieving high-fidelity wavefront shaping and correction in complex media. Despite this, current methods for sampling transmission matrices are susceptible to errors introduced by spurious interference, drift, and field reconstruction methods. In this work, we present a robust differential algorithm that is capable of overcoming these common challenges. Ultimately, our differential algorithm in the presence of common-mode noise and drift yields improvements of 40 to over 100% in field reconstruction fidelity for transmission through a multimodal fiber when compared to previous methods with uncompensated common-mode noise contributing 0.3% of the total input power. While results are presented for a multimodal fiber system, our methodology is applicable to any complex media, paving the way for robust wide-field imaging in real-world applications.

We demonstrate monolithic, etchless dielectric-loaded microring resonators on thin-film lithium tantalate (TFLT), in which a lithographically patterned electron-beam resist strip (ARP 6200.13) serves as the permanent waveguide load on an unetched 300-nm lithium tantalate film. The devices achieve intrinsic quality factors up to 1.23×10[6] in the C band and approximately 9.0×10[5] in the O band, corresponding to propagation losses of approximately 0.4 dB/cm. To our knowledge, this is the first demonstration of resist-loaded microring resonators on TFLT and the highest intrinsic quality factor reported for a monolithic, etchless dielectric-loaded TFLT platform. These results establish dielectric loading as a fabrication-simplified route to high-Q integrated photonics on TFLT, reducing fabrication to a single lithography step without etching, dielectric deposition, or wafer bonding.

We experimentally realize nonhermiticity-induced higher-order topological insulators in fractal-like photonic lattices with first-generation Sierpinski gaskets serving as unit cells. By introducing controllable optical loss into specific waveguides, we demonstrate that nonhermiticity can drive the system from a trivial phase to a nontrivial topological phase, enabling the emergence of corner and edge states. We fabricate the tailored photonic lattices via femtosecond laser direct writing and experimentally observe the loss-induced localization of edge and corner modes. This work not only expands the scope of topological photonic materials, but also opens up new opportunities for the development of reconfigurable topological photonic devices.

Flexible perovskite light-emitting diodes (PeLEDs) are promising for wearable and foldable displays, but their performance is often limited by substrate-related issues like high roughness and poor thermal stability. This work reports a highly efficient, mechanically robust red PeLED utilizing polybenzimidazole (PBI) as the flexible substrate. Compared with the traditional PET substrates, PBI has lower surface roughness and better wettability for the functional layer. As a result, the PeLED based on the PBI substrate achieves a maximum external quantum efficiency (EQE) of 15.7% and a maximum luminance of 3680 cd m[-2], demonstrating excellent mechanical stability. This study proves that PBI, as a high-performance flexible substrate, holds immense potential for realizing high-efficiency and mechanically stable PeLEDs.

In this work, we experimentally investigate the self-pulsating dynamics and excitability of two-section InP quantum-well lasers heterogeneously integrated on silicon. By appropriately tuning the electrical bias conditions, we realize multiple neuronal-like self-pulsating regimes, demonstrating resonate-and-fire and integrate-and-fire-like dynamics, highlighting the potential of the device as a high-speed photonic neuron. A systematic investigation of laser design parameters, including cavity length and gain/saturable absorber (SA) ratio, elucidates their impact on self-pulsation-related properties, such as pulse repetition frequency, and traces the operational parameter space that unlocks stable spiking. Finally, we demonstrate the basic attributes of integrate-and-fire dynamics in the integrated laser-neurons, paving the way toward scalable neuromorphic photonic integrated circuits (PIC) combining low-loss silicon synapses with versatile laser neurons.

This publisher's note contains corrections to Opt. Lett.50, 3209 (2025).

We propose and demonstrate an ultra-broadband mode converter based on phase-shifted long-period gratings operating at the dispersion turning point. The device employs a sidewall-etched LPG in a polymer few-mode waveguide, where two optimized π-phase shifts broaden the resonant dip. Simulations show a -10 dB bandwidth of 745 nm for conversion between the E11 and E21 modes. The fabricated device shows a mode conversion efficiency higher than 15.6 dB over the wavelength range from 1285 to 1825 nm for both TE and TM polarizations. The proposed device provides a compact and fabrication-tolerant solution for mode-division multiplexing and broadband optical interconnects.

Recently, optical skyrmions with polarization topological structures have been extended from the spatial domain to spatiotemporal dimensions. However, previously reported spatiotemporal Laguerre-Gaussian (STLG) skyrmions are limited to a single skyrmion unit, and their topological texture degrades during propagation. Here, we theoretically propose and numerically investigate spatiotemporal Hermite-Gaussian (STHG) skyrmions, characterized as a multiunit skyrmion array within the spatiotemporal plane. Numerical results show that the central skyrmion array, excluding the outermost units, maintains an average skyrmion number above 0.8 over 10 Rayleigh lengths, and that the STHG skyrmions exhibit self-healing ability against partial obstructions, with the topological texture recovering after 1-1.5 Rayleigh lengths of propagation.

We report dual-comb spectroscopy of the collective zero-quantum response of rubidium atoms. The observed signals include two-atom collective resonances at 2(ω D 2 -ω D 1), ω5P3/2→5D-ω D 2 , ω5P3/2→5D-ω D 1 , and (ω D 2 -ω D 1)+(ω5P3/2→5D-ω D 1), as well as higher-order three-atom resonances. Unlike double-quantum spectroscopy, which probes sum-frequency resonances of multiple atoms, the zero-quantum pathway probes difference-frequency correlations between optical transitions. In a dual-comb implementation, these signals are independent of the carrier-envelope offset frequencies of both combs, enabling rapid measurements without active carrier-envelope offset stabilization. These results show that zero-quantum dual-comb spectroscopy is a powerful approach for probing collective coherences and many-body correlations in atomic systems.