The phase spectrum encodes spatial translations of fine structural features in images, offering unique physical insights distinct from conventional amplitude-based measurements. Here, we propose a novel technique, transient image phase spectroscopy (TIPS), integrating phase-resolved image analysis with ultrafast spectroscopy to extract carrier diffusion coefficients by tracking phase evolution across a time series of images. Unlike amplitude spectrum, the phase spectra of the time-resolved carrier dynamic images exhibit intrinsic immunity to overall intensity change arising from carrier recombination. Moreover, the dynamic features of the phase spectrum can be leveraged to effectively distinguish and suppress system noise. These 2 types of fundamental robustness enable reliable diffusion characterization under low signal-to-noise conditions where traditional amplitude-based methods fail. Through numerical simulations and experimental validation, we demonstrate the superior performance of TIPS, including the successful determination of high hot-carrier diffusion coefficients (~130 cm2 s−1) in a rough-surface boron arsenide (BAs). For TIPS decouples spatial dynamics from amplitude decay and fluctuations, we anticipate that this phase-based paradigm will advance innovation in optical and optoelectronic measurement.
Since the first generation of attosecond pulses, observing electron dynamics on their intrinsic time scale became possible, which enabled breakthroughs across various fields, such as the revisit of tunneling time after long debate. Attosecond strong-field physics employing terawatt attosecond pulse represents another vital research front, analogous to how the advent of intense femtosecond lasers enabled the discovery of unprecedented phenomena 40 years ago. However, generation of attosecond pulses with terawatt peak power is extremely challenging, hindering the development of strong-field laser physics. In this work, we theoretically propose and design a tabletop 10-TW-class attosecond light transient in the visible regime, employing an inline spectral–temporal optical parametric amplification scheme that combines C(NH2)3BF4 (GFB) and BaB2O4 crystals. Building upon the experimentally obtained nearly 3-octave seed spanning 0.35 to 2.5 μm, our simulations yield a 524-as-duration light field transient with 7.7-mJ pulse energy and 14.7-TW peak power at 1 kHz. Furthermore, we show flexible waveform manipulation by precisely controlling the phase and spectral shape in the parametric amplification process, enabling tailored attosecond electric fields such as double-peaked, π-shifted, sawtooth-like, and square-like waveforms. The tabletop design first extends GFB-based optical parametric amplification to the attosecond regime and introduces ultraviolet amplification across 350 to 450 nm. Such a high-power attosecond light transient covering the ultraviolet–visible–near-infrared spectrum will advance attosecond nonlinear and strong-field physics and offer a potential tool for applications in biomolecules, quantum materials, and cold atomic systems.
Squeezed states of light and entangled photon source are fundamental resources for quantum science and technology, enabling advances in quantum communication, computation, and precision metrology. Here, we experimentally demonstrate the generation of ultrabright squeezed vacuum and entangled photon pairs via type-I high-gain parametric down-conversion. Using femtosecond pump pulses at 1,030 nm, we produce ultrabright squeezed vacuum with pulses energies on the order of 10 μJ at a central wavelength of 2,060 nm, corresponding to a photon number exceeding 10 14 . By implementing SU(1,1) interferometric configuration, we achieve flexible control over the mode structure, allowing the transition between multimode entangled photon pairs and nearly single-mode squeezed states. This results provide a high-intensity quantum light source that facilitates the study of nonclassical ultrafast dynamics.
Relativistic polarized mid-infrared (mid-IR) pulses hold promising applications in strong-field physics, ultrafast science, and astrophysics such as the acceleration of laser wakefields, investigation of ultrafast processes, detection of young stellar objects, and exploration of various astronomical phenomena. However, due to the damage threshold of crystals and the nonlinear effect of relativistic lasers, it is still a great challenge to generate and manipulate the relativistic mid-IR pulse via traditional optical components. Here, we propose a novel method to generate relativistic polarized mid-IR pulse sources via laser–plasma interaction. When a relativistic laser pulse propagates into a transversely magnetized gas plasma, a nonlinear plasma wake is excited, resulting in the generation of a long-wavelength mid-IR pulse via photon deceleration. On the other hand, due to the phase difference between the ordinary wave and the extraordinary wave components caused by the relativistic magneto-birefringence effect, the polarization of the mid-IR pulse can be manipulated from linear to elliptical, and even to circular. Three-dimensional particle-in-cell simulations demonstrate that the relativistic polarized mid-IR optical source is achievable with a center wavelength of 8.3 µm, a duration of 66.4 fs, and a spectral width of 6.3 to 16.7 µm. Especially, the light polarization can be manipulated by adjusting the drive laser polarization angle and the strength of the external magnetic field. This relativistic polarized mid-IR source generated in a compact and efficient manner can offer new opportunities for strong-field physics, attosecond science, and laboratory astrophysics.
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.
Squeezed states of light and entangled photon source are fundamental resources for quantum science and technology, enabling advances in quantum communication, computation, and precision metrology. Here, we experimentally demonstrate the generation of ultrabright squeezed vacuum and entangled photon pairs via type-I high-gain parametric down-conversion. Using femtosecond pump pulses at 1,030 nm, we produce ultrabright squeezed vacuum with pulses energies on the order of 10 μJ at a central wavelength of 2,060 nm, corresponding to a photon number exceeding 1014. By implementing SU(1,1) interferometric configuration, we achieve flexible control over the mode structure, allowing the transition between multimode entangled photon pairs and nearly single-mode squeezed states. This results provide a high-intensity quantum light source that facilitates the study of nonclassical ultrafast dynamics.
Understanding how molecular structures evolve after photoexcitation is a central question in ultrafast chemistry. Ultrafast electron diffraction (UED) and time-resolved x-ray diffraction (TRXD) enable direct observation of these processes by recording transient diffraction patterns on the femtosecond timescale. For isotropic medium such as liquid and gas, diffraction data are routinely analyzed through the isotropic pair distribution function (PDF), which describes averaged one-dimensional (1D) atomic distances but omits all angular information. When the pump laser is polarized, a transient anisotropy is created in diffraction patterns by the photoselection rule, which provides an opportunity to retrieve the 3D structure of target molecules. In order to achieve this goal, angle-resolved pair distribution function (ARPDF) was developed, although its liquid-phase application has been limited by strong intermolecular contributions. To address this limitation, we developed a generalized optimization method, angle-resolved GPU-accelerated optimization for liquid structure (ARGOLIS), which is designed for ARPDF analysis while remaining fully compatible with traditional PDF-based fitting. Using liquid-phase CCl4 as a test model, we systematically compared the performance of the 2 fittings. Our results show that ARPDF-based fittings can reconstruct both intra- and intermolecular structural changes with high accuracy, while PDF-based fittings may yield structurally ambiguous solutions even when the overall fit quality appears satisfactory. In addition, we show that the output of PDF- and ARPDF-based fittings remains stable even when thermal motions are considered. Our results demonstrate that ARPDF offers a more reliable route for retrieving 3D structural dynamics in time-resolved diffraction experiments, establishing a foundation for future liquid-phase structural retrieval.
Ultrafast laser pulses with broad bandwidth can simultaneously excite multiple quantum states, forming coherent superpositions. The phases of the associated optical transitions evolve in time, giving rise to spectral line profiles that range from symmetric Lorentzian to asymmetric Fano-like forms. Yet, the line shape relations between different transitions within such superpositions remain largely unexplored. Here, we use transient absorption spectroscopy to probe transitions from coherent superpositions. While each transition’s line profile evolves over time, the relative line shape relations between different transitions remain fixed. We identify 4 fundamental types of line shape relations, each producing distinct spectral signatures. These relations naturally arise from second-order perturbation processes and can be actively tuned via the laser–matter interaction strength. Our findings establish a pathway for line shape-engineered control across atomic and molecular systems.
Strong-field nonsequential double ionization (NSDI) is a key process for probing electron–electron correlations. Yet, while its classical aspects are well understood, the quantum nature of these correlations has remained largely hidden. Here, we report the direct observation of subcycle 2-electron quantum interference in the NSDI of xenon. This observation was achieved using triple-coincidence momentum spectroscopy with 400-nm laser pulses at relatively low intensities. The interference stems from the coherent superposition of time-delayed recollision–excitation with subsequent ionization pathways with electron exchange. Strong-field approximation simulations qualitatively reproduce the interference patterns and reveal that they encode the information about the time delay between recollision of the first electron and ionization of the second electron. This work demonstrates a new route for time-resolving quantum-correlated electron dynamics with attosecond precision.
We show that the quantum force that the electrons in a molecule exert on the nuclei remains local even in the presence of strong nonadiabatic interactions. At every geometry, the total force is the sum of a potential gradient term driven by the local population and a nonclassical, nonadiabatic force driven by the local electronic coherence. On the nonadiabatic seams, the nonadiabatic force competes effectively with the potential terms. Following a sudden photoionization, we show how the nonadiabatic component of the local force drives the dynamics of the structural Jahn–Teller rearrangement of the methane cation toward the C 2 v geometry using 2 effective nuclear coordinates and 3 coupled electronic states for either CH 4 + or CD 4 + . Toward the progress in reaching shorter femtosecond resolution in time-resolved x-ray and electron diffraction experiments, our work provides a quantitative understanding and pictorial visualization of the local forces that drive ultrafast molecular rearrangement and chemical reactivity with a special reference to the role of electronic coherences and nonadiabatic couplings.
This work demonstrates deterministic control over the morphology of nanoplasma shock waves generated from isolated gold nanoparticles using temporally delayed dual-pulse femtosecond laser irradiation. By employing angle-resolved proton momentum imaging and multiscale numerical modeling that combines particle-in-cell simulations with a dissipative Gross–Pitaevskii equation framework, we reveal that the formation of highly structured shock waves—specifically, a distinctive triple-lobed pattern observed at a ~20 ps interpulse delay—stems from the resonant absorption of the second laser pulse by an expanding nanoplasma with a tailored density profile. Our findings indicate that the eventual profile of the shock wave is sensitive to the initial distribution of the involved particles at the arrival of the second laser pulse, with optimal coupling achieved when the plasma density nears the critical density. This ability to precisely shape nanoplasma shock waves opens promising avenues for applications in, e.g., compact laser-driven ion accelerators and targeted radiation-mediated therapies.
Quantum coherence plays a fundamental role in driving ultrafast molecular dynamics, but its observation in highly excited states of polyatomic molecules remains rare. Here, using time-resolved photoelectron spectroscopy (TRPES), we report the observation of coherent vibrational quantum beating in the predissociation dynamics of the SF6 molecule, triggered by a 14.1-eV extreme ultraviolet laser pulse. We observe the temporal oscillation profile of TRPES intensity with a period of 318 fs, arising from the interference between different vibrational states separated by 0.013 eV. Supported by ab-initio calculations of potential-energy surfaces, we identify the vibrational states responsible for these observations and extract the lifetimes of both coherences and populations. This work opens pathways to understand and ultimately control the role of coherence in photochemical processes of complex molecular systems.
High-order harmonic generation enables the up-conversion of intense infrared or visible femtosecond laser pulses into extreme-ultraviolet attosecond pulses. However, the highly nonlinear nature of the process results in low conversion efficiency, which can be a limitation for applications requiring substantial pulse energy, such as nonlinear attosecond time-resolved spectroscopy or single-shot diffractive imaging. Refocusing of the attosecond pulses is also essential to achieve higher intensities but difficult in practice due to strong chromatic aberrations. In this work, we address both the generation and the refocusing of attosecond pulses by sculpting the driving beam into a ring-shaped intensity profile with no spatial phase variations, referred to as a hollow Gaussian beam. Our experimental and theoretical results reveal that hollow Gaussian beams efficiently redistribute the driving-laser energy in a ring-shaped area at focus, where the harmonics are generated with low divergence. In addition, unlike in standard Gaussian-driven schemes, this divergence decreases with increasing harmonic order. Although generated as a ring, our numerical simulations show that the attosecond pulses produced in such an extended area can be refocused with greatly reduced chromatic spread therefore enabling higher intensities—up to 3 times compared to those generated with Gaussian driving beams with the same Rayleigh length. This approach opens pathways for compact and powerful attosecond light sources driven by structured light beams.
Breaking the optical diffraction limit is essential for advancing nanotechnology. This perspective discusses the advances of dual-beam nanoscale fabrication strategies, inspired by stimulated emission depletion microscopy, in enabling next-generation optical data storage and neuromorphic computing. It introduces the synergistic use of excitation and inhibition laser beams to enable super-resolution lithography, surpassing the diffraction limit to achieve feature sizes below 20 nm in photoresists and 90 nm in laser-scribed graphene. Key breakthroughs include petabit-capacity 3-dimensional optical disk memory using aggregation-induced emission materials and subdiffraction patterning of graphene for devices. Next, to achieve a breakthrough in computational power, the applications of these super-resolution techniques for fabricating optical neural networks are further outlined. We also highlight the integration of graphene-based optoelectronic synapses with optical neural networks, enabling nonvolatile information processing and paving the way for fully integrated optical neuromorphic architectures that combine sensing, storage, and processing with unprecedented energy efficiency.
Quantum tomography (QT) has found broad applications across multiple disciplines, such as atomic and molecular physics, quantum optics, quantum computing, and quantum information. Here, we provide a comprehensive overview of QT applied to atoms and molecules, which enables the full reconstruction of quantum states when combined with state-of-the-art ultrafast imaging techniques, such as velocity map imaging, photoelectron spectroscopic imaging, and ultrafast electron diffraction imaging. QT reconstructs the quantum states for a variety of ultrafast molecular dynamics processes, including photoionization, dissociation, rotational wave packet alignment, and electronic state internal conversion. By providing fully quantum-mechanical descriptions, the tomographically reconstructed quantum states unveil a range of nonclassical phenomena, such as the spatial interference of wave packets, Dyson orbitals of photoionized molecules, and entanglement between parent ions and emitted electrons in multichannel photoionization.
Advances in attosecond technology enable the measurement of nonlinear light–matter interaction at unprecedented timescales. However, attosecond-resolved nondipole processes in nonlinear photoionization, especially for partial wave resolved transition, still remain elusive, in the face of the challenges in identifying weak nondipole contributions from a background of dipole-allowed electronic dynamics. In this theoretical work, we employ circularly polarized extreme ultraviolet and infrared pulses to facilitate the unambiguous characterization of nondipole electronic dynamics, from 2-photon interferometric signals of angle-resolved photoelectron spectra. It is found that the ionized electronic waves via nondipole quantum transitions are notably delayed by around 10 as compared with dipole waves in their dispersion through atomic potential near 10 eV, which unravels how the centrifugal potential specifically affects both nondipole bound–continuum and continuum–continuum transitions.
Electron orbitals are quantum-mechanical wave functions that describe the spatial distribution of an electron, with the square of their magnitude representing the electron density. The concept of orbital forms foundation for visualizing and understanding the microscopic structure of atoms and molecules. We theoretically demonstrate how twisted x-ray diffraction can be employed to characterize the spatial profile of electron orbitals unambiguously. Using the hydrogen atom as a model system, we derive exact analytical expressions for its ground and excited states and show that twisted x-rays enable a clearer distinction between these states compared to standard x-ray diffraction. In particular, we highlight how the characteristic spatial profile of twisted beams, arising from their orbital angular momentum, overcomes technical limitations of standard x-ray diffraction, providing precise and unambiguous sensitivity to orbital spatial structure. We further demonstrate the applicability of this framework to realistic molecular systems by presenting ab initio x-ray diffraction signatures of Rydberg-excited oxazole, showing that large orbital angular momentum of the incident twisted x-rays enhances the distinction between the pi-3s and pi-3p Rydberg states. Our results lay the groundwork for the application of twisted x-ray diffraction to more complex systems with potential extensions to valence-bonded molecular orbitals.
Ultrafast electron diffraction (UED) is a powerful tool for probing atomic-scale dynamics with femtosecond temporal resolution and angstrom-level spatial precision. It enables direct observation of structural changes in non-equilibrium systems, including photoinduced transformations, phase transitions, and chemical reactions. While large-scale MeV facilities have advanced UED, the growing demand for accessible, laboratory-scale instruments highlights the need for compact solutions. We present a compact electrostatic UED instrument developed in our laboratory. Operating at a cathode voltage of 100 kV, the source produces similar to 200-fs (full width at half maximum) electron pulses in a low areal density regime (<0.1 electrons mu m(-2)), primarily limited by the duration of the driving ultraviolet pulse. Analytical estimations and N-particle tracer simulations indicate that, with ultrashort laser excitation and enhanced high-voltage conditioning to boost the extraction field, the temporal response could approach the 50-fs threshold. Combined with multi-kilohertz repetition rates, this balance of pulse duration and average beam brightness ensures both ultrafast performance and robust diffraction signals. Initial static and dynamic diffraction experiments, performed at similar to 0.05 electrons mu m(-2) and 6 kHz, validate the instrument's baseline performance and sensitivity. These results demonstrate the potential for capturing ultrafast structural dynamics within a compact, laboratory-scale platform.
The aqueous-phase mass spectra of acetone, aniline, and cytidine were measured by our liquid-microjet time-of-flight mass spectrometer equipped with a femtosecond laser ionization source. In comparison with their gas-phase mass spectra, their aqueous-phase mass spectral peaks exhibit much broader and richer features. Parent fragment clusters with H2O molecules [e.g., (CO-H2O)+, (C5H4NH2-H2O)+, (C4H3NH2-(H2O)2)+, and (NH2-(H2O)5)+] for aqueous-phase acetone, aniline, and cytidine were assigned and analyzed, indicating a distinctive fragmentation pattern of parent ions in their native aqueous environments. By controlling the energies of the femtosecond ionization laser, parent fragment clusters are verified to be mainly ejected from the bulk side of the liquid microjet rather than the gas region around the liquid microjet. From a mechanistic perspective, femtosecond multiphoton dissociative ionization is tentatively proposed to explain the mechanism of production and fragmentation of parent ions in bulk aqueous solution. Additionally, ion diffusion and ion Coulomb repulsion are also applicable to respectively explain the mechanisms of the ion migration from bulk to surface and ensuing ion ejection from surface into vacuum. To our knowledge, this is the first time that we demonstrate the experimental feasibility of the measurement of aqueous-phase mass spectra and propose mechanistic insights into femtosecond photoionization and fragmentation of bulk aqueous molecules.
