Phase-coherent optical frequency transfer is essential for optical clock networking, relativistic geodesy, and distributed precision metrology. However, realizing coherent optical networks spanning thousands of kilometers in standard single-mode fiber (SMF) generally requires densely distributed amplifiers or repeater stations together with complex operational control, while long-term instability remains limited by thermally driven residual phase fluctuations. Here we show that hollow-core fiber (HCF) can simultaneously improve transfer instability and relax the reach limitation of long-span optical frequency transfer. Compared with SMF, HCF exhibits lower fiber-induced phase noise and shorter propagation delay, supporting improved short-term instability, while its much lower thermal sensitivity supports nearly one-order-of-magnitude better long-term instability. In addition, for long-haul HCF links, no observable stimulated Brillouin scattering induced saturation is found up to the maximum available injected power of 34 dBm, whereas the threshold of an equal-length SMF link remains only a few dBm. Together with the lower attenuation achievable in modern HCF, this enables ultra-long single-span optical frequency transfer. Using a 152 km HCF link with an average attenuation of 0.18 dB/km, we demonstrate single-span optical frequency transfer, achieving a fractional frequency instability of 7.3 x 10^-21 at 10,000 s and a fractional uncertainty of 1.8 x 10^-20. These results establish HCF as a transmission medium that simultaneously improves instability and extends single-span reach, opening a practical route toward future intercontinental optical frequency networks with ultrahigh precision.

We present the design and progress towards a 200mJ pulse energy, 5kHz rep-rate, 1kW average power, 40fs multidimensionally combined fiber laser for laser-plasma acceleration and broad applications, including overcoming challenges due to broad bandwidth.

Single-mode, record high 7.7mJ stored energy extraction from a monolithically integrated fiber amplifier is demonstrated using 85µm-core chirally-coupled-core fiber and counter pumped tapered end cap technologies, enabling integration of high-energy pulsed fiber laser arrays.

Structured optical waveforms are emerging as powerful control fields for the next generation of complex photonic and electromagnetic systems, where the temporal structure of light can determine the ultimate performance of scientific instruments. However, identifying optimal optical drive fields in strongly nonlinear regimes remains challenging because the mapping between optical inputs and system response is high-dimensional and typically accessible only through computationally expensive simulations. Here, we present a physics-guided deep learning framework for the inverse design of optical temporal waveforms. By training a light-weighted surrogate model on simulations, the method enables gradient-based synthesis of optical profiles that compensate nonlinear field distortions in driven particle-field systems. As a representative application, we apply the approach to the generation of electron beams used in advanced photon and particle sources. The learned optical waveform actively suppresses extrinsic emittance growth by more than 52

We present recent impedance modeling studies of the kicker systems developed for the Advanced Light Source Upgrade (ALS-U), including ferrite-loaded kickers, stripline-type fast kickers, and septa. The modeling supports the injection/extraction systems to ensure beam stability in the accumulator and storage rings. In addition, it provides guidance for component fabrication and offline testing by incorporating realistic factors such as mechanical tolerances and assembly specifications.

A novel machine-learning based closed-loop control system to enhance spatial transverse stability of high-power lasers, overcoming the bandwidth limitations of traditional feedback systems. Tested at the BELLA Center, it achieved sub-μrad stability, marking the first successful predictive control in high-power low-repetition-rate facility.

High-power lasers are vital for particle acceleration, imaging, fusion and materials processing, requiring precise control and high-energy delivery. Laser plasma accelerators (LPAs) demand laser positional stability at focus to ensure consistent electron beams in applications such as X-ray free-electron lasers and high-energy colliders. Achieving this stability is especially challenging for the low-repetition-rate lasers in current LPAs. We present a machine learning method that predicts and corrects laser pointing instabilities in real-time using a high-frequency pilot beam. By preemptively adjusting a correction mirror, this approach overcomes traditional feedback limits. Demonstrated on the BELLA petawatt laser operating at the terawatt level (30 mJ amplification), our method achieved root mean square pointing stabilization of 0.34 and 0.59 $\unicode{x3bc} \mathrm{rad}$ in the x and y directions, reducing jitter by 65% and 47%, respectively. This is the first successful application of predictive control for shot-to-shot stabilization in low-repetition-rate laser systems, paving the way for full-energy petawatt lasers and transformative advances across science, industry and security.

Laser plasma accelerators, typically operating at 1-10 Hz repetition rates, have the ability to produce high-quality electron beams in compact, all-optical-driven configurations, with the electron beams uniquely suited for a wide variety of accelerator-based applications. However, fluctuations and drifts in the laser delivery to the meter-scaled and below plasma target (the electron beam source) will translate into electron beam source variations that can limit their utility for demanding applications like light sources or linear colliders. Commercially available active feedback laser stabilization systems are intrinsically bandwidth limited due to their integration with multi-inch corrective mirror mounts which minimizes their effectiveness. In this manuscript, we present a Neural Network time series forecaster that can predict laser position fluctuations of the laser delivery to the final target well ahead of a future laser shot. The Root-Mean-Square-Error (RMSE) of the prediction accuracy was <2 mu m for a 1/e(2) beam radius of 34 mu m. Our feed-forward approach serves as a first-step in circumventing the bandwidth limitations imposed by the currently available stabilization systems since it allows for mirrors to be moved into position ahead of time to offset the predicted future position drift. This will help advance laser plasma accelerator research by providing greater robustness and stability needed for its applications.

Ultraintense laser interactions with a metal foil offer an emerging approach toward the generation of intense terahertz (THz) radiation, and how to improve the THz generation efficiency remains an open question. Here, we report the enhanced generation of THz radiation from ultraintense laser-irradiated nanostructured targets where metallic nanorod arrays are fabricated on the front surface of foil targets. The influences of nanorod lengths on the THz radiation emitted from the foil rear surface are investigated experimentally. Compared to the case of flat foil targets, a maximum enhancement in the THz pulse energy by a factor of 2.3 is observed by varying the nanorod length, and the THz peak emission direction moves toward the target surface with longer nanorods. Measurements of escaping fast electrons imply that the boosted THz yield is attributed to the enhanced laser absorption, and thus, the substantial increase in the fast-electron number. Particle-in-cell simulations reproduce well the experimental results.

We introduce a deep-learning method for modeling dynamic gain and non-linearities in ultrafast fiber amplifiers, overcoming li mitations of ph ysics-based models. Trained and tested with experiments, the algorithm can predict accurately, adaptable to varying amplifier conditions.

We theoretically and experimentally show coherent pulse stacking (CPS) can accommodate tens-of-fs pulse durations and has negligible stacking fidelity degradation with increased pulse bandwidth. Simulations prove large number of tens-of-fs pulses can be stacked with high pre-pulse contrast. In an experiment, nine spectrally broadened and fiber amplified pulses are stacked using four cascaded cavities. CPS of pulses with different spectral bandwidths, up to 75 nm base-to-base (<50 fs transform-limited duration), are tested, showing negligible stacking degradation due to increased bandwidth. This work provides a path towards high energy, tens-of-fs pulses from ultrafast fiber lasers.

Gas-insulated metal-enclosed transmission lines have the advantages of high capacity, low loss and reliability, and have the prospect of wide application. Currently, insulation failure is the primary cause of equipment failure. In this paper, combining the principle and test method of ultrasonic detection, the detection technology of defects and cracks of tri-post insulators based on ultrasonic guided wave is investigated. A platform for ultrasonic signal detection of tiny defects of insulators is constructed, and the reflective and refractive properties of defects to the ultrasonic guided wave conduction are verified within the COMSOL simulation platform, which proves the reliability of ultrasonic detection of crack defects. The EMD-wavelet thresholding multiple noise reduction algorithm is utilized to achieve post-processing, and the typical signal characteristics of different types of material defect models are analyzed. The signal-to-noise ratio and root-mean-square (RMS) evaluation indexes are introduced, obtaining a signal-to-noise ratio of 21.847 and a RMS error of 0.041, which are superior to other noise reduction methods. Ultrasonic detection of different types, materials and defects of materials, the two low peak distribution of epoxy matrix and silicone rubber containing defects is concluded, which provides theoretical basis and experimental guidance for subsequent ultrasonic insulation detection.

We report the femtosecond time -resolved dynamics of relativistic electron pulses in ultraintense laserfoil interactions, by characterizing the terahertz self -radiation with single -shot ultrabroadband interferometry. Experimental measurements together with theoretical modeling reveal that the electron pulses inherit the duration of the driving laser pulse. We also visualize the electron recirculation dynamics, where electrons remain trapped inside the self -generated electrostatic potential well and rebound back and forth around the thin foil for hundreds of femtoseconds. Our results not only demonstrate an in situ , real-time metrology scheme for electron bursts, but also have important implications for understanding and manipulating the time -domain properties of laser -driven particle and radiation sources.

We demonstrate ultra-broadband spectral combining of three fiber chirped-pulse amplifiers using two coherently-spectrally synthesized pulse shapers. The combined pulses are compressed to 42fs, the shortest from a spectrally-combined fiber system at one-micron wavelength.

In this work, non-destructive virtual diagnostics are applied to retrieve the electron beam time of arrival and energy in a relativistic ultrafast electron diffraction (UED) beamline using independently-measured machine parameters. This technique has the potential to improve temporal resolution of pump and probe UED scans. Fluctuations in time of arrival have multiple components, including a shot-to-shot jitter and a long-term drift which can be separately addressed by closed loop feedback systems. A linear-regression-based model is used to fit the beam energy and time of arrival and is shown to be able to predict accurately behavior for both on long and short time scales. More advanced time-series analysis based on machine learning techniques can be applied to improve this prediction further.

We demonstrated 55-fs pulses from spectrally combining two chirped-pulse fiber channels operating at partially-overlapped spectral bands, with a pulse shaper incorporated in each channel. The spectral intensity and phase shaping in two fiber channels are coherently-spectrally synthesized by phase-synchronizing the two channels at the overlapped spectrum. To the best of our knowledge, 55 fs is the shortest pulse duration from a spectrally combined fiber system at one-micron Yb wavelength, and this work is the first demonstration of coherent spectral synthesis of two pulse shapers. This work provides a promising path toward high-energy, tens-of-fs fiber chirped-pulse amplifier systems.

Silicon nitride (Si3N4) is an excellent engineering ceramic with high strength, fracture toughness, wear resis-tance, and good chemical and thermal stability. Recently, the enhanced thermal conductivity enables Si3N4 to have potential application prospects in the electronic and orthopedic fields. Metal bonding with Si3N4 is often the key to these applications. Here we report a facile approach for the titanium-activated Cu bonding on Si3N4 substrates using an atmosphere plasma spray (APS) process. With X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) observation, it was shown that the interaction between the pre-bonded Ti (by APS) on Si3N4 promoted the adhesion and high bonding strength of APS Cu on Si3N4. The interfacial structure and phases were characterized, and tensile strength, electrical resistivity, thermal conduc-tivity, and residual stress of Cu bonded Si3N4 were measured accordingly. The APS deposited Cu layer is dense, has a high purity, and is joined firmly with Ti pre-bonded Si3N4 substrate. The maximum tensile strength be-tween Cu and Si3N4 is as high as 89.4 MPa. The Si3N4 substrate bonded with highly dense Cu demonstrates a low surface resistivity of 8.72 x 10-4 & omega;& BULL;mm, and high thermal conductivity of 98.12 W/m & BULL;K, which shows potential applications in electronic devices.

We demonstrate ultra-broadband spectral combining of ultrashort pulses from Yb-doped fiber amplifiers, with coherently spectrally synthesized pulse shaping, to achieve tens-of-fs pulses. This method can fully compensate for gain narrowing and high order dispersion over broad bandwidth. We produce 42fs pulses by spectrally synthesizing three chirped-pulse fiber amplifiers and two programmable pulse shapers across an 80nm overall bandwidth. To the best of our knowledge, this is the shortest pulse duration achieved from a spectrally combined fiber system at one-micron wavelength. This work provides a path toward high-energy, tens-of-fs fiber chirped-pulse amplification systems.

We theoretically prove coherent pulse stacking can accommodate tens-of-fs pulse lengths when stacking large number of pulses. Experimental validation shows high-efficiency stacking of nine, 50fs bandwidth pulses with four Gires-Tournois Interferometric (GTI) cavities.