arXiv subjects

Peixiang Lu

Publications and source records attributed to Peixiang Lu.

At least 37 records · Page 2Linked to original sources

arXiv2025

Reconfigurable chiral edge states in synthetic dimensions on an integrated photonic chip

Chiral edge state is a hallmark of topological physics, which has drawn significant attention across quantum mechanics, condensed matter and optical systems. Recently, synthetic dimensions have emerged as ideal platforms for investigating chiral edge states in multiple dimensions, overcoming the limitations of real space. In this work, we demonstrate reconfigurable chiral edge states via synthetic dimensions on an integrated photonic chip. These states are realized by coupling two frequency lattices with opposite pseudospins, which are subjected to programmable artificial gauge potential and long-range coupling within a thin-film lithium niobate microring resonator. Within this system, we are able to implement versatile strategies to observe and steer the chiral edge states, including the realization and frustration of the chiral edge states in a synthetic Hall ladder, the generation of imbalanced chiral edge currents, and the regulation of chiral behaviors as chirality, single-pseudospin enhancement, and complete suppression. This work provides a reconfigurable integrated photonic platform for simulating and steering chiral edge states in synthetic space, paying the way for the realization of high-dimensional and programmable topological photonic systems on chip.

physics.optics↗

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

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↗

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

High-purity valley-polarized currents induced by bichromatic optical fields in two-dimensional materials

Producing currents predominantly from a single valley, namely valley-polarized currents, at optical-cycle timescales is an important aspect of the petahertz valleytronics, yet it remains less developed. This work exhibits the feasibility of achieving this goal using bichromatic optical fields, which allow for the precise control of sub-cycle electron dynamics. The combined effect of the helical and asymmetric waveforms of the optical fields leads to highly asymmetric excitation at different valleys and displacement of the excited electrons concurrently, thereby inducing valley-polarized currents with high valley purity, on the sub-optical-cycle timescale. Inherently, the purity of the currents built up from the optical approach remains high even for materials with short decoherence time. Moreover, the direction of the currents can be precisely controlled by adjusting the relative phase of the bichromatic components. Our work offers a promising avenue for generating and modulating high-purity valley-polarized currents at the femtosecond timescale, facilitating the development of petahertz valleytronics.

physics.optics↗

arXiv2024

Spatio-spectral light modulator of XUV high harmonics

High-order harmonic generation (HHG), characterized by its highly nonlinear nature, often exhibits a complex spatio-temporal profile that poses challenges for practical applications. In this study, we unveil a method for manipulating the spatio-spectral distribution of HHG by guiding the recollision electron trajectory in the spatio-temporal domain using a control field. The resulting far-field high harmonic (HH) radiation inherits the intricate spatio-temporal characteristics of the control field, showcasing diverse features including spatial tilting, spectral shifting, and emission angle deflection. Using the relative delay between the control field and the driving pulse as the primary control parameter, we achieve precise tailoring of the high harmonics in the spatio-spectral domain. This controllability in HH benefits ultrafast metrology and imaging applications in the extreme ultraviolet (XUV) regime.

physics.optics↗

arXiv2024

Helicity-selected near-circularly polarized attosecond pulses generated from mixed He-Ne gases

We present and theoretically demonstrate a method for generating helicity-selected near-circularly polarized attosecond pulses in mixed He-Ne gases using bichromatic counter-rotating circularly polarized (BCCP) fields. High-order harmonics driven by BCCP fields exhibit circular polarization for individual orders in the frequency domain, but adjacent orders have opposite helicities. By utilizing the He-Ne mixture, we select only one helical component of the harmonics, resulting in the generation of highly elliptically polarized attosecond pulses in the time domain. Our analyses based on the quantum-orbit theory and the strong field approximation further clarify that the polarization of attosecond pulses is governed by the interference mechanism of high-order harmonics emitted by He and Ne. This combination of BCCP fields and an atomic mixture which requires no alignment in experiments, significantly simplifies the generation of elliptically polarized harmonics dominated by one helical component, thereby paving the way for an efficient and robust method to generate bright attosecond pulses with large ellipticity.

physics.optics↗

arXiv2024

Compact ultra-broadband light coupling on chip via nonadiabatic pumping

Enlarging bandwidth capacity of the integrated photonic systems demands efficient and broadband light coupling among optical elements, which has been a vital issue in integrated photonics. Here, we have developed a compact ultra-broadband light coupling strategy based on nonadiabatic pumping in coupled optical waveguides, and experimentally demonstrated the designs in thin-film lithium niobate on insulator (LNOI) platform. We found that nonadiabatic transition would produce a decreased dispersion of the phases related to eigenstates in the waveguides. As a consequence, we realized high-efficiency directional transfer between edgestates for various wavelengths covering a 1-dB bandwidth of ~320 nm in experiment (>400 nm in simulation), with a coupling length (~50 μm) approximately 1/10 of that required in the adiabatic regime. Furthermore, we have constructed complex functional devices including beamsplitter and multiple-level cascaded networks for broadband light routing and splitting. Our work preserves significant advantages simultaneously in extending the operation bandwidth and minimizing the footprint, which demonstrates great potential for large-scale and compact photonic integration on chip.

physics.optics↗

arXiv2024

Spectral multiplexing based on multi-distance lensless imaging

We have demonstrated the capability of spectral multiplexing in multi-distance diffractive imaging, enabling the reconstruction of samples with diverse spectral responses. While previous methods like ptychography utilize redundancy in radial diffraction data to achieve information multiplexing, they typically require capturing a substantial amount of diffraction data. In contrast, our approach effectively harnesses the redundancy information in axial diffraction data. This significantly reduces the amount of diffraction data required and relaxes the stringent requirements on optical path stability.

physics.optics↗

arXiv2024

Circularly polarized RABBIT applied to a Rabi-cycling atom

We utilize the reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) technique to study the phase of a Rabi-cycling atom using circularly polarized extreme ultraviolet and infrared (IR) fields, where the IR field induces Rabi oscillations between the 2s and 2p states of lithium. Autler-Townes splittings are observed in sidebands of the photoelectron spectra and the relative phases of outgoing electron wave packets are retrieved from the azimuthal angle. In this RABBIT scheme, more ionization pathways beyond the usual two-photon pathways are required. Our results show that the polar-angle-integrated and polar-angle-resolved RABBIT phases have different behaviors when the XUV and IR fields have co- and counter-rotating circular polarizations, which are traced back to the different ionization channels according to the selection rules in these two cases and their competition relying on the propensity rule in laser-assisted photoionization.

physics.atom-ph↗

arXiv2023

Efficient spectral broadening and few-cycle pulse generation with multiple thin water films

High-energy, few-cycle laser pulses are essential for numerous applications in the fields of ultrafast optics and strong-field physics, due to their ultrafast temporal resolution and high peak intensity. In this work, different from the traditional hollow-core fibers and multiple thin solid plates, we represent the first demonstration of the octave-spanning supercontinuum broadening by utilizing multiple ultrathin liquid films (MTLFs) as the nonlinear media. The continuum covers a range from 380 to 1050 nm, corresponding to a Fourier transform limit pulse width of 2.5 fs, when 35 fs Ti:sapphire laser pulse is applied on the MTLFs. The output pulses are compressed to 3.9 fs by employing chirped mirrors. Furthermore, a continuous high-order harmonic spectrum up to the 33rd order is realized by subjecting the compressed laser pulses to interact with Kr gas. The utilization of flowing water films eliminates permanent optical damage and enables wider and stronger spectrum broadening. Therefore, this MTLFs scheme provides new solutions for the generation of highly efficient femtosecond supercontinuum and nonlinear pulse compression, with potential applications in the fields of strong-field physics and attosecond science.

physics.optics↗

arXiv2023

High Harmonic Generation in Solids: Particle and Wave Perspectives

High harmonic generation (HHG) from gas phase atoms (or molecules) has opened up a new frontier in ultrafast optics, where attosecond time resolution and Angstrom spatial resolution are accessible. The fundamental physical pictures of HHG are always explained by the laser-induced recollision of particle-like electron motion, which lay the foundation of attosecond spectroscopy. In recent years, HHG has also been observed in solids. One can expect the extension of attosecond spectroscopy to the condensed matter if a description capable of resolving ultrafast dynamics is provided. Thus, a large number of theoretical studies have been proposed to understand the underlying physics of HHG. Here, we revisit the recollision picture in solid HHG and show some challenges of current methods with particle perspective, and present the recently developed wave perspective Huygens-Fresnel picture in understanding dynamical systems within the ambit of strong-field physics.

physics.optics↗

arXiv2022

Magnetic-Field effect in Laser-assisted XUV ionization

The magnetic-field effect of the laser pulse is investigated in laser-assisted XUV ionization. By numerically solving the three-dimensional time-dependent Schrödinger equation, we find that the photoelectron momentum distribution is distorted by the magnetic-field effect of the IR streaking field. It results in a transverse-momentum- and time-delay-dependent longitudinal photoelectron momentum shift, which is further analytically confirmed by employing the nondipole corrected strong field approximation. We also demonstrate that the magnetic field does not affect the time shift retrieved from the streaking spectrum, although the streaking spectrum is apparently altered by the momentum shift induced by the magnetic-field effect. Our work reveals the time-resolved nondipole effect of the laser pulse by the attosecond streaking technique.

physics.atom-ph↗

arXiv2022

All-optical spatio-temporal metrology for isolated attosecond pulses

Characterizing an isolated attosecond pulse (IAP) is essential for its potential applications. A complete characterization of an IAP ultimately requires the determination of its electric field in both time and space domains. However, previous methods, like the widely-used RABBITT and attosecond streaking, only measure the temporal profile of the attosecond pulse. Here we demonstrate an all-optical method for the measurement of the space-time properties of an IAP. By introducing a non-collinear perturbing pulse to the driving field, the process of IAP generation is modified both spatially and temporally, manifesting as a spatial and a frequency modulation in the harmonic spectrum. By using a FROG-like retrieval method, the spatio-spectral phases of the harmonic spectrum are faithfully extracted from the induced spatio-spectral modulations, which allows a thoroughgoing characterization of the IAP in both time and space. With this method, the spatio-temporal structures of the IAP generated in a two-color driving field in both the near- and far-field are fully reconstructed, from which a weak spatio-temporal coupling in the IAP generation is revealed. Our approach overcomes the limitation in the temporal measurement in conventional in situ scheme, providing a reliable and holistic metrology for IAP characterization.

physics.optics↗

arXiv2022

Fingerprint of the Interbond Electron Hopping in Second-Order Harmonic Generation

We experimentally explore the fingerprint of the microscopic electron dynamics in second-order harmonic generation (SHG). It is shown that the interbond electron hopping induces a novel source of nonlinear polarization and plays an important role even when the driving laser intensity is 2 orders of magnitude lower than the characteristic atomic field. Our model predicts anomalous anisotropic structures of the SHG yield contributed by the interbond electron hopping, which is identified in our experiments with ZnO crystals. Moreover, a generalized second-order susceptibility with an explicit form is proposed, which provides a unified description in both the weak and strong field regimes. Our work reveals the nonlinear responses of materials at the electron scale and extends the nonlinear optics to a previously unexplored regime, where the nonlinearity related to the interbond electron hopping becomes dominant. It paves the way for realizing controllable nonlinearity on an ultrafast time scale.

physics.optics↗

arXiv2021

Nondipole effects on the double-slit interference in molecular ionization by xuv pulses

The double-slit interference in single-photon ionization of the diatomic molecular ion $\mathrm{H}_2^+$ is theoretically studied beyond the dipole approximation. Via simulating and comparing the interactions of the prealigned $\mathrm{H}_2^+$ and the hydrogen atom with the xuv pulses propagating in different directions, we illustrate two kinds of effects that are encoded in the interference patterns of the photoelectrons from $\mathrm{H}_2^+$: (i) the photon-momentum transfer and (ii) the finite speed of light. While both effects could modify the maxima of the interference fringes, we show that the former one hardly affects the interference minima. Our results and analysis show that the interference minima rule out the influences of the photon-momentum transfer and, potentially, the multielectron effect, thus performing a better role in decoding the zeptosecond time delay for the pulse hitting one and the other atomic centers of the molecule.

physics.atom-ph↗

arXiv2020

Strong field induced electron density tide in high harmonic generation from solids

In strong laser fields, the electron density in solids can show up tidal motions caused by the laser ``pulling'' on the electrons, which forms an electron density tide (EDT). However, the strong field processes in solids are always explained by the single-active-electron (SAE) model and the fluctuation of background electrons is neglected previously. Here, we demonstrate the strong field induced EDT effect and propose a model for revealing its role in high harmoinc generation (HHG) from solids. We show that the EDT effect induces an additional polarization current beyond the SAE approximation. It gives a new mechanism for HHG and leads to new anisotropic structures, which are experimentally observed with MgO. Our experiment indicates that the EDT effect becomes more obvious with increasing the laser intensity. Our work establishes the bridge between the HHG and the microscopic EDT in solids induced by the strong laser field, which paves the way to probe the ultrafast electron dynamics.

physics.optics↗

arXiv2019

Dynamical switching of lasing emission by exceptional point modulation in coupled microcavities

In a non-Hermitian optical system with loss and gain, an exceptional point (EP) will arise under specific parameters where the eigenvalues and eigenstates exhibit simultaneous coalescence. Here we report a dynamical switching of lasing behavior in a non-Hermitian system composed of coupled microcavities by modulating the EPs. Utilizing the effect of gain, loss and coupling on the eigenstates of coupled microcavities, the evolution path of the eigenvalues related to the laser emission characteristics can be modulated. As a result, the lasing emission property of the coupled cavities exhibits an dynamical switching behavior, which can also be effectively controlled by tuning the gain and loss of the cavities. Moreover, the evolution behavior in a more complicated system composed of three coupled microcavities is investigated, which shows a better tunability compared with the two-microcavity system. Our results have correlated the EPs in non-Hermitian system with lasing emission in complex microcavity systems, which shows great potential for realizing dynamical, ultrafast and multifunctional optoelectronic devices for on-chip integrations.

physics.optics↗