arXiv subjects

Peixiang Lu

Publications and source records attributed to Peixiang Lu.

At least 19 recordsLinked to original sources

arXiv2026

Topologically Configurable Nonlinear Vortex Generation at van der Waals Heterostructures

van der Waals (vdW) materials offer a highly tunable and efficient platform at nanoscale for nonlinear and quantum optics. Twist-stacked vdW heterostructures enable elegant control of symmetry and interlayer coupling. Prior studies mainly focus on planar twisted interfaces, while neglecting the naturally formed and mandatory defects in such vdW heterostructures. Here, we demonstrate nonlinear singular optics with topologically configurable nonlinear vortex generation at the corner singularity of vdW heterostructures. By tailoring azimuthally discrete second-harmonic phase gradients at each interface, we obtain programmable nonlinear vortex emitters with dominant target OAM components. Nonlinear OAM beams with topological charge $\ell = 1$ and $\ell = -2$ are experimentally realized, respectively. Our work unlocks the untapped potentials of nonlinear singular optics in twisted vdW materials as a reconfigurable and lithography-free platform for nonlinear structured light generation, important in quantum nonlinear optics and related fields.

physics.optics↗

arXiv2026

Nondipole Contributions to Attosecond Chiral Photoionization Asymmetries

Photoelectron circular dichroism (PECD) reads molecular chirality from forward-backward asymmetries in photoelectron emission, but the same observable can also contain non-dipole contributions from photon momentum transfer. Here we show that such contributions can reshape attosecond PECD measurements in both one- and two-photon ionization of chiral molecules. Calculations beyond the dipole approximation, interpreted with perturbation theory, reveal that non-dipole effects modify not only the magnitude but also the phase of the emitted electron wave packet. In two-photon interferometry, pathway interference amplifies the non-dipole response and can reverse the apparent chiral asymmetry. We further identify a practical separation principle: the non-dipole component is insensitive to enantiomeric handedness and can therefore be obtained from a racemic mixture. Subtracting this background isolates the purely chirality-induced asymmetry, enabling more accurate measurements of chiral electron dynamics.

physics.atom-ph↗

arXiv2026

Vortex photoelectron holography in strong-field tunneling ionization

Vortex electrons, characterized by a helical phase front, offer unique advantages for probing material structures. Such electrons can be generated via tunneling ionization in strong laser fields. In this paper, we investigate the rescattering dynamics of vortex photoelectrons by the parent ion. Specifically, we introduce vortex photoelectron holography, extending conventional strong-field photoelectron holography (SFPH) from plane-wave to vortex rescattering. By solving the time-dependent Schr\"{o}dinger equation, we extract the vortex scattering phase from the SFPH fringes, showing excellent agreement with scattering calculations. Thus, our work provides direct access to the vortex scattering phase, paving the way for applying SFPH to structurally sensitive imaging with phase-engineered photoelectrons.

physics.atom-ph↗

arXiv2026

Anomalous Autler-Townes Splitting in Resonant Multiphoton Ionization Driven by Bright Squeezed Vacuum

Bright squeezed vacuum (BSV) light has a vanishing mean optical electric field yet can strongly enhance strong-field nonlinear responses beyond the conventional semiclassical paradigm. Here we examine this scenario in the light-matter strong-coupling regime by investigating resonant multiphoton ionization of atoms driven by BSV, using a fully quantum treatment of both the electron and the field. Our results show that the photoelectron energy spectrum exhibits an anomalous Autler-Townes splitting whose magnitude grows with the Above-threshold-ionization (ATI) order, rather than remaining essentially ATI-order independent as in the case of coherent driving. This behavior reflects a general scaling with the number of absorbed photons and originates from the broad photon-number fluctuations of the driving field together with the resulting electron-field entanglement. We further show that the BSV-induced enhancement of ionization yields evolves with intensity, crossing over from the $g^{(p+1)}$ limit to the $g^{(p)}$ limit as Rabi oscillations become established. These results identify a quantum regime of strong-field ionization governed by the interplay of photon statistics, nonlinear transitions, strong coupling, and nonseparable light-matter dynamics.

physics.atom-ph↗

arXiv2026

6.2-GW tabletop attosecond light source

The generation of attosecond pulses (1 as=10-18 s) has enabled real-time observation and manipulation of coherent electron dynamics, yet their low peak power has hindered the development of advanced attosecond pump-probe spectroscopy and attosecond nonlinear metrology. Here we overcome this limitation by generating 1.64 uJ, 263 as isolated attosecond pulses with a peak power of 6.2 GW, the highest pulse energy and peak power reported for a tabletop isolated attosecond source. This is achieved by combining a 2.1 TW, few-cycle (8.3 fs) two-color synthesizer with a loose focusing geometry that enables macroscopic phase-matching. The synthesizer features a stabilized carrier-envelope phase and an actively synchronized relative time delay between the two-color channels, ensuring high stability and reproducibility. This robust tabletop attosecond source enables nonlinear effect experiments that were previously inaccessible with lower-power IAPs, establishing a foundation for advanced attosecond spectroscopy and nonlinear metrology.

physics.optics↗

arXiv2026

Robust quantized transport from topological quasienergy winding in long-range-coupling synthetic quantum walks

Quantized transport is a prominent feature in topological physics, with canonical examples being the quantum Hall effect and adiabatic Thouless pump, which are based on the Chern number, a topological invariant of 2D systems. Going beyond the Chern-number-based paradigms, quantized transports can also arise from k-direction quasienergy winding unique to periodically driven (Floquet) systems, which are free of dimensionality and adiabaticity limitations. However, lattices displaying winding of their quasienergy bands require asymmetric long-range couplings that are difficult to achieve in lattices of real-space coupled sites. Here, by leveraging photonic synthetic dimensions we construct asymmetric long-range-couplings in a one-dimensional temporal quantum walk based on three coupled fiber loops. We demonstrate quantized transport arising from the winding of quasienergy bands in k direction. We show that the average group velocity of an initial wave packet is proportional to the winding number, which leads to a quantized transport displacement. To better visualize this quantized displacement, we cascade two regions with flipped nearest/long-range couplings and observe a focusing effect with a quantized spatial shift in the focusing point. We also probe the robust properties of quantized transport against obstacles and disorders. The study initiates quasienergy-winding-based topological transports, which can feature applications in precise and robust imaging and information processing.

physics.optics↗

arXiv2026

Quantum Trajectory Separation and Attosecond Mapping in Liquid High-Harmonic Generation

High-harmonic generation (HHG) from liquids offers a potential pathway to attosecond spectroscopy in chemically complex and disordered environments, yet fundamental questions remain open: whether liquid harmonic emission preserves well-defined attosecond synchronization, and whether harmonic emission can involve simultaneous contributions from multiple quantum trajectories with distinct excursion times despite strong disorder and scattering. Here, we address these issues experimentally by resolving the trajectory-dependent temporal structure of liquid HHG. By optimizing the laser focusing geometry, we achieve clear spatial discrimination of short- and long-trajectory contributions, providing direct evidence for the existence of multiple quantum trajectories in liquids. Using a phase-controlled two-color driving field, we independently retrieve the attochirp associated with each trajectory and demonstrate opposite energy-time correlations for short and long trajectories, establishing a trajectory-resolved energy-time mapping in liquid HHG. All observations are well reproduced by semiclassical recollision simulations. These results place liquid HHG on the same conceptual footing as gas- and solid-phase HHG and establish a robust foundation for attosecond-resolved spectroscopy of ultrafast electronic and chemical dynamics in liquid environments.

physics.optics↗

arXiv2025

Universal convolution from wave dynamics: photonic processing and encryption in synthetic dimension

Convolution, a cornerstone of signal processing and optical neural networks, has traditionally been implemented by mapping mathematical operations onto complex hardware. Here, we overcome this challenge by revealing that wave dynamics in translation-symmetric lattices intrinsically performs convolution, with the dispersion relation uniquely defining the complex-valued kernel. Leveraging this universal principle, we develop a convolutional architecture of minimal complexity through wave evolution in programmable photonic synthetic lattices, delivering high-throughput, multifunctional capabilities at a rate of 13.5 tera-operations per second (TOPS) for image processing. Beyond convolution acceleration, the kernel's complex nature facilitates the photonic simulation of both irreversible diffusion and reversible unitary quantum dynamics under classical incoherent excitation. Capitalizing on the physics-based reversibility and undetectable phase information, we demonstrate a novel convolution-driven optical encryption strategy. This work establishes a unified framework for photonic computing by grounding convolution in wave dynamics, opening avenues toward scalable, multifunctional photonic processors with high integration potential.

physics.optics↗

arXiv2025

Direct Mapping of Intrinsic Topology of Bound States in the Continuum via Nonlinear Emission

The direct mapping of the intrinsic topology in a leaky photonic band is crucial and challenging in topological photonics. For instance, observables in bound states in the continuum (BICs) feature complex topological textures such as a polarization vortex in momentum space, which nonetheless is difficult to be characterized in far-field scattering, especially considering the dominant direct channel. Here, we propose and experimentally demonstrate a hybrid nonlinear metasurface that enables a direct visualization of the intrinsic topology in BICs via second-harmonic generation (SHG). The enhanced local-source of SHG from the ultrathin indium tin oxide can effectively excite the emissions from the eigenmodes of a TiO2 photonics crystal slab, achieving three-order enhancement of SHG magnitudes. Importantly, these enhanced SH emissions carry topological polarization textures of BICs to the far field. With this, we can directly construct polarization vector maps of symmetry-protected BICs and chiral symmetry-broken quasi-BICs, clearly visualizing the winding structure around V points, the generation and evolution of chiral C points. This work provides a universal approach for characterizing topological photonic systems via coherent nonlinearity processes, opening new avenues for studying topological phenomena in non-Hermitian photonic systems.

physics.optics↗

arXiv2025

Quantum Path Control in High-Order Harmonic Generation via Squeezed Lights

High-order harmonic generation (HHG), a robust tabletop source for producing attosecond pulses, has been extensively utilized in attosecond metrology. Traditionally, HHG driven by classical laser fields involves two typical quantum paths (short and long quantum paths) contributing to harmonic emission. Here, we demonstrate that these quantum paths in HHG can be selectively controlled using squeezed lights, a form of non-classical light. Our results indicate that the long (short) quantum path of HHG will be dramatically suppressed in the phase (amplitude)-squeezed fields. The time-frequency analysis reveals that this quantum path control stems from the quantum fluctuations in the squeezed light, which modify the phase matching of harmonic emission from different quantum states of the squeezed light. Such a quantum path selection can be achieved for the whole harmonic plateau, which has great potential to generate ultrashort isolated attosecond pulse with duration less than one atomic unit of time.

physics.optics↗

arXiv2025

Complete suppression of the non-dipole drift effect in high harmonic generation

In high harmonic generation (HHG), non-dipole effects become increasingly significant at long driving wavelengths, as the magnetic field leads to a lateral drift of the continuum electron, which disrupts the electron recollision and inhibits the harmonic emission. To address this problem, we revisit the dynamics of the continuum electrons under electromagnetic fields in the HHG process and show that the magnetic effect on the drift includes a fundamental-frequency and a double-frequency component. By adding an additional field to counteract the double-frequency effect caused by the magnetic field, we construct an effective linearly polarized field that recovers the recollision of all returning electrons to the parent ion. Consequently, the harmonic yield is restored and becomes the same as the result within the dipole approximation across the broad spectral range. This work provides a scheme that completely suppresses the non-dipole drift effect and fully compensates for the harmonic yield reduction, paving the way to efficiently generate coherent radiation in the range from extreme ultraviolet to soft x-ray and ultrashort pulses based on HHG.

physics.optics↗

arXiv2025

Clean few-cycle blue soliton self-compressed pulses generation in hollow-core fibers

Blue pulses with few-cycle temporal durations hold significant value in attosecond science and ultrafast spectroscopy. In this work, we combine efficient broadband frequency doubling, multiplate continuum (MPC) post-compression and blue soliton self-compression in hollow-core fibers (HCF), experimentally demonstrating HCF-based 4.4 fs clean blue soliton self-compressed pulse. Our scheme offers three-fold advantages: (1) prevention of excessive dispersion accumulation by gradually suppressing dispersion through multi-stage design; (2) enhanced overall efficiency for self-compression-based ultrashort blue pulse generation; and (3) elimination of dispersion compensation components for the final spectral broadening stage compared to post-compression schemes. This work extends HCF-based self-compression soliton to the blue spectral region and paves the way for generating energetic ultrashort blue pulses.

physics.optics↗

arXiv2025

Instantaneous optical selection rule for independent control of valley currents

We reveal an instantaneous optical valley selection rule that illuminates the coupling between the instantaneous optical chirality of the driving laser field and the chirality of valley systems. Building on this principle, we propose and demonstrate that a single chirality-separated optical field, in which oppositely signed instantaneous optical chiralities are separated within an optical cycle, enables independent manipulation of currents from K and K' valleys. Based on this scheme, we highlight two key example applications: (1) complete separation of currents from different valleys, yielding 100%-purity valley-polarized currents, and (2) generation of pure valley current with zero net charge flow. Our work offers a robust and highly controllable all-optical strategy for ultrafast engineering valley currents in the optical cycle timescale, paving a new avenue for valleytronics and quantum information technologies.

physics.optics↗

arXiv2025

Unveiling unique ultrafast nonlinearities in liquid-phase high-order harmonic generation

High-order harmonic generation (HHG) provides a powerful optical tool for probing ultrafast dynamics on the attosecond timescale. While its mechanisms in gases and solids are well-established, understanding nonlinear optical responses in liquids remains challenging. The absence of long-range order in liquids questions the applicability of the existing HHG models developed in other media. Through combined experimental and theoretical investigations, we identify unique characters of liquid-phase HHG -- spectral redshift and broadening, which are fundamentally distinct from both the gaseous and solid-state counterparts. Quantitative measurements and simulations of HHG in liquids illustrate a near linear dependence of harmonic redshift and broadening on the laser intensity, with the nonlinear response of water exceeding that of ethanol. The simulations reveal that these features arise from delocalized electronic states with energy loss in multiple scatterings and transient Stark shift during their transitions in laser fields. Meanwhile, we find that liquid polarity or hydrogen bond exerts decisive control over the transition dipole momentum distributions of delocalized states. Our findings establish a nonlinear spectral method for probing the internal network in liquids, paving the way for studying its role in chemical and biological processes.

physics.optics↗

arXiv2025

Attosecond-Resolved Photoionization Dynamics and Interference-Enhanced Photoelectron Circular Dichroism in Chiral Molecules

Chiral molecules exhibit enantiosensitive light-matter interactions, with photoelectron circular dichroism (PECD) serving as a sensitive probe of molecular chirality through the asymmetry in the photoelectron wavepacket amplitude. Here, we demonstrate a photoelectron interferometric approach to access the phase of the photoelectron wavepacket and uncover attosecond dynamics in chiral molecule photoionization. Using circularly polarized attosecond XUV pulse trains synchronized with IR fields, we reveal distinct time delays between forward- and backward-ejected photoelectrons in a randomly oriented ensemble of chiral molecules. Moreover, we predict a pronounced enhancement of PECD due to the interference of the two photoionization pathways. The forward-backward time delay difference and the PECD are more prominent when the IR field counter-rotates with the XUV field. These results imply the counter-rotating IR field is more efficient in generating odd-parity photoelectron wavepackets in continuum-continuum transitions, highlighting the critical role of long-range chiral potential. Our work demonstrates a way of coherent control over the chiral photoelectron wavepackets, providing a route to enhance chiral signals and manipulate ultrafast chiral dynamics on attosecond time scales.

physics.atom-ph↗

arXiv2025

"Molecular waveplate" for the control of ultrashort pulses carrying orbital angular momentum

Ultrashort laser pulses carrying orbital angular momentum (OAM) have become essential tools in Atomic, Molecular, and Optical (AMO) studies, particularly for investigating strong-field light-matter interactions. However, controlling and generating ultrashort vortex pulses presents significant challenges, since their broad spectral content complicates manipulation with conventional optical elements, while the high peak power inherent in short-duration pulses risks damaging optical components. Here, we introduce a novel method for generating and controlling broadband ultrashort vortex beams by exploiting the non-adiabatic alignment of linear gas-phase molecules induced by vector beams. The interaction between the vector beam and the gas-phase molecules results in spatially varying polarizability, imparting a phase modulation to a probe laser. This process effectively creates a tunable ``molecular waveplate'' that adapts naturally to a broad spectral range. By leveraging this approach, we can generate ultrashort vortex pulses across a wide range of wavelengths. Under optimized gas pressure and interaction length conditions, this method allows for highly efficient conversion of circularly polarized light into the desired OAM pulse, thus enabling the generation of few-cycle, high-intensity vortex beams. This molecular waveplate, which overcomes the limitations imposed by conventional optical elements, opens up new possibilities for exploring strong-field physics, ultrafast science, and other applications that require high-intensity vortex beams.

physics.optics↗

arXiv2024

Attosecond All-Optical Retrieval of Valley Polarization via Circular Dichroism in Transient Absorption

We propose a scheme for retrieving the ultrafast valley polarization (VP) dynamics in two-dimensional hexagonal materials via attosecond circular dichroism (CD) transient absorption spectroscopy. This approach builds on the CD transition between the first and higher conduction bands induced by the circularly polarized probe pulses. The population imbalance at nonequivalent valleys in the first conduction band is proportionally mapped onto the difference in absorption coefficients of two probe pulses with opposite helicities, supporting an unprecedented quantitative retrieval of the corresponding VP dynamics with subfemtosecond time resolution. We theoretically demonstrate the scheme for h-BN and MoS2 through ab initio calculations, achieving an accurate retrieval of the VP dynamics, particularly the transient VP switching processes, with a time resolution of 250 as.

physics.optics↗

arXiv2024

Interface and spectrum multiplexing ptychographic reflection microscopy

Reflective ptychography is a promising lensless imaging technique with a wide field of view, offering significant potential for applications in semiconductor manufacturing and detection. However, many semiconductor materials are coated with different layers during processing, which leads to the reflected diffraction light being a coherent superposition of multiple light beams. Traditional phase recovery methods often overlook the multi-layered nature of these materials, resulting in artificial errors and, in some cases, failures in image reconstruction. This limitation has hindered the broader application and adoption of reflection ptychography. Here, we propose and experimentally demonstrate an innovative interface and spectrum multiplexing ptychographic reflection microscopy. By employing multi-wavelength light as the illumination source, our approach enables the accurate extraction of the wavelength-dependent surface structure imaging and topography mapping of materials in a single experiment. This advancement offers a reliable technique for element-specific detection of semiconductor materials, utilizing tabletop extreme ultraviolet light sources in the future.

physics.optics↗