Attosecond x-ray pulses are a critical tool for tracking ultrafast electron dynamics in condensed matter, molecular systems, and strongly correlated materials. Recent breakthroughs have pushed x-ray free-electron lasers (XFELs) into the attosecond domain, substantially surpassing their previous femtosecond capabilities. Building on these advancements, this work investigates the potential of the Shanghai HIgh repetitioN rate XFEL and Extreme light facility (SHINE), China’s first continuous-wave (CW) XFEL, to generate intense attosecond x-ray pulses, thereby offering transformative capabilities for x-ray science. Through comprehensive start-to-end simulations, we show that SHINE is capable of producing terawatt-scale pulses at both soft and hard x-ray ranges. This is achieved using a self-chirping scheme within the existing machine configuration, requiring no additional hardware. We further find that superradiant behavior in the postsaturation regime plays a central role in attosecond XFEL, enabling higher peak power and shorter attosecond pulses. Our results illustrate the wide applicability of the self-chirping scheme and demonstrate that CW XFELs can generate intense attosecond x-ray pulses at megahertz repetition rates, opening new opportunities for real-time studies of electronic dynamics in complex systems.

Extremely high axial magnetic fields above the gigagauss level are supposed to exist in neutron stars, which may be a one of the critical parameters for their internal structures and be responsible for the x-ray and gamma-ray emission from these stars. Here, we show that such ultrahigh magnetic fields can be produced by multiple petawatt-class lasers interacting with a cuboid solid target with a cylindrical microtube in the middle. It is found that the obliquely incident intense lasers at the target surfaces enable the produced hot electrons to form an azimuthal current and subsequently induce a seed magnetic field along the cylindrical axis inside the microtube as the hot electrons transport into it. This current–field configuration is similar to a theta-pinch device. When the hot electrons and energetic ions produced via target normal sheath acceleration converge toward the microtube axis, the seed magnetic field is dramatically amplified. This process continues until the magnetic pressure near the axis becomes comparable to the thermal pressure contributed both by hot electrons and by energetic ions. Later on, as the plasma in the center starts to be expelled outward by the magnetic pressure, an electron current ring with extremely high densities is formed, leading to a further boost of the magnetic fields to well above the gigagauss level. A scaling of the magnetic field strength with laser intensities, pulse durations, incident angles, and target sizes is presented and verified by numerical simulations, which demonstrates the robustness of our scheme. Our scheme is well suited for experimental realization on 100-TW-class to PW-class femtosecond or picosecond laser facilities with multiple linearly polarized laser beams.

Ultrafast dynamics observed at low energies carry insightful information about the complex many-body interactions in solid-state materials. Here, we present a highly sensitive and robust setup for asymmetric 2-dimensional spectroscopy performing 2-pulse visible excitation combined with probing in the 15- to 35-THz frequency range. This experimental setup is ideal for targeting the interplay of high- and low-energy correlations in functional materials with femtosecond temporal and millielectronvolt energy resolution. In addition, the sub-cycle field resolution of mid-infrared pulses enables tracking nonthermal interactions in the complex dielectric function. Prototypical measurements benchmark ultrafast carrier dynamics in thin-film graphite, showing in detail the interplay of direct and indirect optical transitions in the transient excited state. We further investigate the photo-induced collapse of the superconducting condensate in the high-temperature superconductor Bi 2 Sr 2 CaCu 2 O 8+ x at energies resonant to the optical bandgap, revealing a nontrivial instantaneous nonlinearity related to the excited quasiparticles in the material. Optical pump–terahertz probe experiments build the foundation for this evolutionary step in 2-dimensional spectroscopy as well as for terahertz 4-wave mixing with resonant driving and readout of the superconducting state. Our results offer exciting perspectives in the study of strong correlations and enable precise investigations of nontrivial many-body interactions in few-layer samples and nanostructures.

Recent advancements in high-energy terahertz (THz) sources, driven by powerful laser systems, now enable the generation of ultrashort THz pulses with energies up to several millijoules, spanning frequencies from 1 to 30 THz. A key breakthrough is developing a reliable single-shot detection method, essential for measuring the electric field of these broadband, low-repetition-rate pulses, which is vital for exploring the complex dynamics of THz emission and studying extreme nonlinear material responses in this range. Existing detection methods have been limited to lower frequencies. Here, we introduce the first potentially single-shot-capable THz detection technique for capturing ultra-broadband waveforms. Utilizing a 1-μm-thick SiN detection chip, we exploit THz field-induced second harmonic generation to achieve real-time monitoring of THz waveforms with frequency content up to 30 THz. By adjusting the angle between the THz and optical probe beams, we can fine-tune the detection window for enhanced flexibility. Our novel THz detector is ideally suited for high-energy, low-repetition-rate sources, unlocking new frontiers in THz research.

In this paper, a series of calibration-free temperature measurement methods based on light-induced thermoelastic spectroscopy (LITES) are proposed for the first time. These techniques utilize the steady-state and transient response characteristics of the quartz tuning fork (QTF), namely, the calibration-free LITES (CF-LITES) and calibration-free heterodyne LITES (CF-H-LITES) methods. Four methods, first harmonic (1 f ) difference signal to normalize the second harmonic (2 f ) fundamental signal (method I, 2 f fund /1 f diff ), 1 f overtone signal to normalize the 2 f fundamental signal (method II, 2 f fund /1 f over ), 1 f heterodyne difference signal to normalize the 2 f heterodyne fundamental signal (method III, 2 f - H fund /1 f-H diff ), and 1 f heterodyne overtone signal to normalize the 2 f heterodyne fundamental signal (method IV, 2 f-H fund /1 f-H over ), for simultaneously detecting 1 f and 2 f within the frequency response range of the QTF are proposed to achieve calibration-free measurement. A self-designed T-shaped QTF with low fundamental and overtone frequencies was used to increase the energy accumulation time, thereby enhancing the sensor signal level. A 3-stage tube furnace was adopted to verify the performance of these 4 methods. Experimental results showed that the errors for the 4 methods were less than 4%, with a standard deviation below 11 °C. Furthermore, the calibration-free method, which employs normalization of the 2 f signal with the 1 f signal, effectively mitigates the impact of laser beam jitter and power fluctuations on detection performance. A superior performance can be obtained by adopting the CF-H-LITES technique based on method IV. It not only has excellent detection performance but also reduces the measurement period to 4 s, which is about 5 times faster. This development shows substantial promise for expanding the application of the CF-LITES and CF-H-LITES techniques in harsh environments.

The Fano line shape, arising from the interference of pathways for the excitation of discrete and continuum states, plays a fundamental role in many branches of physics, chemistry, and materials science. Exciting the resonance with a high harmonic provides naturally a phase delay between the pathways leading to a complex asymmetry parameter. We demonstrate that its amplitude and phase can be controlled on the femtosecond and attosecond time scales, respectively. With our high-energy-resolution (10-meV) experiment, we dynamically image a resonance-enhanced electron wave packet during its temporal evolution, extracting both the amplitude and the phase. Calculations reproduce our experimental results. Our approach constitutes a method for measuring the photoionization delays of a resonance and enables the reconstruction of the electron wave packet in the time domain. This concept of an interference-controlled Fano line shape is a step toward attosecond quantum optics with potential ramifications into nanoscience and next-generation optical materials.

Understanding material structural reaction to light is of utmost importance to advance processing resolution in ultrafast laser volume structuring into the nanoscale. Selective thermodynamic pathways are required to quench energy transport in the most rapid manner and to confine the process to nanometer lengths, bypassing optical resolution. Quantifying material dynamics under confinement, with in situ access to transient local temperature and density parameters, thus becomes key in understanding the process. We report in situ reconstruction of thermodynamic states over the entire matter relaxation path in bulk α -quartz irradiated by ultrafast nondiffractive laser beams using time-resolved qualitative and quantitative optical phase microscopy. Thermooptic dynamics indicate rapid spatially confined crystalline-to-amorphous transition to a hot dense fused silica form. Densification exceeds 20% and the matrix temperature rises to more than 2,000 K in the first nanosecond. This structural state relaxes in hundreds of nanoseconds. The dispersion and time design of the optical beam to picosecond durations increases the spatial confinement and triggers an extreme nanostructuring process based on nanocavitation that occurs within the amorphizing material, where the low-viscosity phase lowers the mechanical requirements for the process. Processing feature scales of less than a tenth of the optical wavelength are obtained in the volume. This allows for structural and morphological nanoscale material features under 3D confinement that can engineer optical materials.

Valleytronic devices based on all-optical ultrafast control are expected to increase the speed of information processing to petahertz and serve a new generation of quantum computers. However, the current difficulty in realizing this vision is the lack of a nondamaging means suitable for ultrafast lasers. We propose a robust scheme to control the valley polarization of monolayer materials, achieved through the quantum interference between 1- and 2-photon transition pathways. The scheme reveals that conventional circularly polarized light is unnecessary for resonantly induced valley polarization and, instead, only a parallel-polarized 2-color field is required. The interference dynamics enables the switch of valley to be manipulated within few femtoseconds without the necessity for extremely strong or single-cycle pulses. The disclosure of this interference scheme enables repetitive operations in valley devices for signal processing at petahertz clock rates without causing material damage. It sheds light on the practical manufacture of high-speed valleytronic devices.

The exploration of optical and photonic phenomena, particularly the modulation of pulse signals and the ultrafast control of light fields at extreme temporal and spatial scales, substantially enhances our understanding of light–matter interactions and broadens the scope of potential applications inspired by metamaterials and metasurfaces. In this perspective, we highlight advancements in ultrafast metaphotonics by introducing ultrafast pulse shaping and control using metadevices. We begin with a detailed exposition of the principles of metasurfaces and evaluate their role in manipulating light fields in high-frequency and terahertz bands, emphasizing the importance of metasurfaces in ultrafast optics. We then present several methods for controlling the output response of metadevices using external physical fields or phase-change materials to achieve active metadevices. Finally, we anticipate the prospects of this field in terms of fundamental research and practical applications. The integration of these 2 disciplines will drive vibrant developments across multiple fields, including biology, chemistry, and materials science.