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Light-induced deprotonation of molecules is an important process in photochemical reactions. Here, we theoretically investigate the tunneling deprotonation of H 2 + and its asymmetric isotopologues driven by circularly polarized THz laser pulses. The quasi-static picture shows that the field-dressed potential barrier is significantly lowered for the deprotonation channel when the mass asymmetry of the diatomic molecule increases. Our numerical simulations demonstrate that when the mass symmetry breaks, the tunneling deprotonation is significantly enhanced and the proton tunneling becomes the dominant dissociation channel in the THz driving fields. In addition, the simulated nuclear momentum distributions show that the emission of the proton is directed by the effective vector potential for the deprotonation channel and, meanwhile, the angular distribution of the emitting proton is affected by the alignment and rotation of the molecule induced by the rotating field. [ABSTRACT FROM AUTHOR]

We experimentally study two-body Coulomb explosions of CO2, O2, and CH3Cl molecules in intense femtosecond laser pulses. We observe an obvious variation in the ionic angular distribution of the fragments with respect to the kinetic energy releases (KERs). Using a classical model based on ab initio potential energy curves, we find that the dependence of the ionic angular distribution on the KER is relevant to the fact that the accurate potential energy deviates significantly from the value determined by applying the Coulomb interaction approximation at a relatively small internuclear distance of the molecule. We show that the KER-dependent ionic angular distribution provides an effective way to determine the critical internuclear distance at which the Coulomb interaction approximation holds or breaks down without relying on the knowledge of the accurate potential energy curves. [ABSTRACT FROM AUTHOR]

We demonstrate a double Rabi splitting totaling 348 meV in an Ag nanocavity embedding of methylene blue (MB) dye layer, which is ascribed to the equilibrium state of monomer and dimer coexistence in MB dye. At low dye concentration, the single-mode strong coupling between the monomer exciton in MB dye and the Ag nanocavity is observed. As the dye concentration is increased, three hybridized plexciton states are observed, indicating a double Rabi splitting (178 and 170 meV). Furthermore, the double anti-crossing behavior of the three hybrid states is observed by tuning the Ag nanocube size, which validates the multi-mode strong coupling regime. It shows clear evidence on the diverse exciton forms of dye molecules, both of which can interact with plasmonic nanocavity, effectively. Therefore, it provides a good candidate for realizing the multi-mode strong coupling.

Background: Renal cell carcinoma (RCC) is presently recognized as the most prevalent kidney tumor. However, the role and underlying mechanism of action of the conversion factor-inducible protein (TGFBI), an extracellular matrix protein, in RCC remain poorly understood. Methods: In this study, we employed Western blot, quantitative real-time polymerase chain reaction (qRT-PCR), and immunohistochemistry techniques to assess the expression of TGFBI in RCC tissues or cells. Furthermore, we analyzed the proliferation and migration of RCC cells using CCK8, cloning, scratching, and migration assays. Additionally, we examined apoptosis and cell cycle progression through flow cytometry, analysis. Lastly, we employed gene set enrichment analysis (GSEA) to investigate the biological processes associated with TGFBI, which were subsequently validated. Results: The findings indicate that TGFBI exhibits significantly elevated expression levels in both renal cell carcinoma (RCC) tissues and cells. Furthermore, the knockdown of TGFBI in SiRNA transfected cells resulted in the inhibition of RCC cell proliferation, migration, invasiveness, apoptosis, and alteration of the cell cycle. Additionally, TGFBI was found to impede the epithelial-mesenchymal transition (EMT) process in RCC cells. Bioinformatics analysis suggests that TGFBI may exert its influence on various biological processes in RCC through the tumor immune microenvironment. Moreover, our study demonstrates that TGFBI promotes RCC progression by activating the PI3K/AKT/mTOR/HIF-1α. Conclusions: Our research indicates that TGFBI exhibits high expression in RCC and facilitate RCC progression and metastasis through various molecular mechanisms. Hence, TGFBI has the potential to be a novel therapeutic target for the diagnosis and treatment of RCC in the future. [ABSTRACT FROM AUTHOR]

The momentum distribution of photoelectrons in H2+ molecules subjected to an attosecond pulse is theoretically investigated. To better understand the laser–molecule interaction, we develop an in-line photoelectron holography approach that is analogous to optical holography. This approach is specifically suitable for extracting the amplitude and phase of the forward-scattered electron wave packet in a dissociating molecule with atomic precision. We also extend this approach to imaging the transient scattering cross-section of a molecule dressed by a near infrared laser field. This attosecond photoelectron holography sheds light on structural microscopy of dissociating molecules with high spatial-temporal resolution. [ABSTRACT FROM AUTHOR]

Refraction is a basic beam bending effect at two media's interface. While traditional studies focus on stationary boundaries, moving boundaries or potentials could enable new laws of refractions. Meanwhile, media's discretization plays a pivotal role in refraction owing to Galilean invariance breaking principle in discrete-wave mechanics, making refraction highly moving-speed dependent. Here, by harnessing a synthetic temporal lattice in a fiber-loop circuit, we observe discrete time refraction by a moving gauge-potential barrier. We unveil the selection rules for the potential moving speed, which can only take an integer v = 1 or fractional v = 1/q (odd q) value to guarantee a well-defined refraction. We observe reflectionless/reflective refractions for v = 1 and v = 1/3 speeds, transparent potentials with vanishing refraction/reflection, refraction of dynamic moving potential and refraction for relativistic Zitterbewegung effect. Our findings may feature applications in versatile time control and measurement for optical communications and signal processing. Here, authors construct a moving potential barrier in a synthetic temporal lattice. They unveil the selection rules for choosing potential moving speed as well as the conditions to achieve transparent moving potentials and refraction. [ABSTRACT FROM AUTHOR]

Parity‐time (PT) and anti‐parity‐time (anti‐PT) symmetries have provided important guiding principles in the research of non‐Hermitian physics. However, realizations of anti‐PT symmetry in photonic systems usually rely on optical nonlinearities and indirect‐coupling approaches. Here, they apply the channel interference principle mediated by synthetic gauge‐flux biasing in open‐cavity systems to construct anti‐PT symmetries. It is shown that a specific π‐flux biasing into a looped‐resonator array can force a frequency degeneracy between pairwise Bloch modes therein. By further coupling the array into two external waveguides with tailored positions of ports, the system near the degeneracy point can be described by an anti‐PT‐symmetric Hamiltonian. When a real gauge‐flux detuning is introduced, the system undergoes a spontaneous transition between anti‐PT and anti‐PT‐broken phases, through which the two extreme cases of complete channel‐drop tunneling and complete tunneling suppression can be switched. Finally, by superimposing a PT‐symmetric term onto the anti‐PT‐symmetric Hamiltonian via applying an imaginary gauge‐flux biasing, extreme channel‐drop amplifying effects can be further realized by exciting the "lasing" mode under the critical‐coupling condition. The work bridges the physical connection between synthetic gauge field and anti‐PT symmetry. This paradigm may also find many applications from optical routing, and switching to buffering and amplifying on a chip–scale platform. [ABSTRACT FROM AUTHOR]

Mode selecting plays a vital role in the field of optoelectronics, such as optical communication, signal processing, on-chip light manipulation, mode conversion, and frequency synthesis. In this work, flexible selection and enhancement of the frequency modes in an unidirectional coupled Su–Schrieffer–Heeger (SSH) frequency lattice are obtained with Floquet exceptional points (EPs) and chiral Zener tunneling (ZT). The unidirectional coupled non-Hermitian SSH frequency lattices are synthesized by a double-ring system with complex dynamical modulations. Under an effective direct current (dc) force induced by the phase-mismatching of the modulations, the two Floquet bands of the non-Hermitian frequency lattices are degenerated and the Floquet EPs arise. Therefore, the unidirectional and irreversible frequency mode conversion takes place, which is the chiral ZT. Moreover, through perturbation analysis and numerical simulations, we prove that the frequency modes of the two-band system can be selected and enhanced by a multi-photon resonance dc force. [ABSTRACT FROM AUTHOR]

A novel method is proposed to directly characterize the exciton‐plasmon coupling in a photosensitive nanoparticle‐on‐mirror (NPoM) nanocavity. Under the illumination of UV light, the localized surface plasmon resonance (LSPR) peaks of the nanocavity can be continuously tuned over a wide range (≈65 nm), enabling precise determination of the energy dispersion relationship of plexcitons in the nanocavity. The results indicate that the energy of Rabi splitting can be actively tuned from 65 meV (weak coupling) to 170 meV (strong coupling) by adjusting the LSPR peak of a specific nanocavity (particle size L≈55‐92 nm) to the exciton wavelength (the zero detuning). In addition, the criterion of strong coupling is optimized by introducing single‐particle absorption spectroscopy. The work offers an intuitive method for the strong coupling characterization in nanocavity, paving the way for the real‐time tuning of coupling strength over a wide range (100 meV) from weak to strong coupling regimes. [ABSTRACT FROM AUTHOR]

An ultrafast fiber laser system comprising two coherently combined amplifier channels is reported. Within this system, each channel incorporates a rod-type fiber power amplifier, with individual operations reaching approximately 233 W. The active-locking of these coherently combined channels, followed by compression using gratings, yields an output with a pulse energy of 504 μJ and an average power of 403 W. Exceptional stability is maintained, with a 0.3% root mean square (RMS) deviation and a beam quality factor M2 < 1.2. Notably, precise dispersion management of the front-end seed light effectively compensates for the accumulated high-order dispersion in subsequent amplification stages. This strategic approach results in a significant reduction in the final output pulse duration for the coherently combined laser beam, reducing it from 488 to 260 fs after the gratings compressor, while concurrently enhancing the energy of the primary peak from 65% to 92%. [ABSTRACT FROM AUTHOR]

Dynamic localization (DL) refers to a wavefunction confinement effect of electrons in periodic lattices under an ac electric field driving. Recent studies have transplanted DLs from electronic to photonic systems using periodically curved waveguide lattices, where the ac electric field is mimicked by the waveguide's bending curvature. However, due to the severe limitations of bending losses and poor tunability for highly curved, arbitrarily shaped waveguides, present studies mainly focus on DL under the simplest sinusoidal‐wave driving; its extension to an arbitrary‐wave driving remains challenging. Here, by constructing a synthetic temporal lattice with a coupled fiber‐loop circuit, the limitations of spatially curved waveguides are circumvented and generalized DLs are experimentally demonstrated under arbitrary‐wave driving. First, by applying band‐collapse criteria, the general conditions for the driving field's symmetry to achieve DLs are revealed. Then, two representative even‐function driving fields of square‐ and triangle‐waveforms are chosen, and wave‐packet revivals are observed as signatures of DLs. As a counter‐example, the breakdown of DL is also verified using odd‐function driving field of sawtooth‐waveform. The work reveals the conditions for realizing generalized DLs and experimentally verifies them using synthetic lattice schemes. This paradigm may find potential applications in versatile temporal‐waveform reshaping, pulse manipulations for optical communications, and signal processing. [ABSTRACT FROM AUTHOR]

We theoretically investigate nonadiabatic effects in tunneling ionization of a hydrogen atom induced by a few-cycle elliptically polarized laser pulse. We find a deflection angle between the maximum of the photoelectron momentum distribution and the direction of the negative vector potential corresponding to the electric-field peak. This deflection angle mainly originates from the fact that the instant of the maximal ionization rate does not exactly correspond to the instant of the electric-field peak in the few-cycle elliptically polarized laser pulse, revealing an ionization time shift between those two instants. The ionization time shift is a result of the nonadiabatic effect induced by the envelope of the few-cycle elliptically polarized laser pulse, which disappears in a long-pulsed laser. Our study is useful for understanding attoclock experiments using few-cycle elliptically polarized laser pulses. [ABSTRACT FROM AUTHOR]

We report an unexplored observation of multi-orbital contribution in the below- and near-threshold harmonic generation of aligned molecules. A typical pump–probe configuration is used in our experiments. By scanning the time delay and crossing angle of polarization directions between the pump and probe pulses, we find that the harmonic yield in this region exhibits abnormal intensity-dependent modulation patterns. Further comparison and analysis show that this observation can be interpreted as due to the contribution of deeper-lying molecular orbitals, which are much more prominent than in the above-threshold region and can overall surpass the contribution of the highest occupied molecular orbital, leading to reversed modulation patterns. The particular importance of the deeper-lying orbitals in this regime is closely related to the multi-photon excitation pathways involved in the generation process. Our work will advance further investigations on the mechanism of below- and near-threshold harmonic generation. [ABSTRACT FROM AUTHOR]

The electron response of nanoplasmon and nanoplasma in the laser field is greatly important for improving the functionality and efficiency of many potential applications. However, how and under what conditions the nanoplasmon‐nanoplasma transition works remains poorly understood due to radiation damage and charge buildup. Utilizing the combined aerodynamic lens and velocity map imaging spectrometer, this transition mediated by different mechanisms are demonstrated, as verified by the distinct photoelectron momentum distributions from Cu nanoparticles. Initially the polarization‐dependent distributions emphasize the domination of surface emission driven by the plasmonic field. Subsequently the transition starts and the competition of volume‐multiphoton and thermionic emission plays the intermediate state dominating the transition process. Finally, a complete plasma is generated with the leading role of thermionic emission, which is confirmed by first observing the correlated electronic decay in metal nanoparticles. These findings bridge the gap between electron emission in nanoplasmonic and nanoplasma states and identify the mechanism‐specific contributions, which will offer general principles for designing nanostructure and laser fields to control electron excitation and emission in practice. [ABSTRACT FROM AUTHOR]

The laser‐irradiated aerosolized nanostructures with complex geometries offer unique opportunities to steer orientation‐dependent photoion emission for multiple applications of directional ion sources and photocatalysis. The orientation‐dependent photoion emission is characterized by measuring the distribution and probability on differently oriented nanostructures. This unique capability is achieved by introducing momentum‐to‐space orientation discrimination in the single‐shot velocity map imaging technique with the aerodynamic lens. The effect of geometry, polarization, and concentration to control the photoion emission from differently oriented nanostructures is introduced for optimizing the potential applications of photoion emission including directional tunable nanoanode and optical sensors. The mechanism behind controlling the photoion emission is visualized by the variations in the regions of high laser intensity inside the nanostructures responding to the orientation, geometry, and polarization. This work represents an advance in characterizing the photoion emission from the randomly oriented aerosolized nanostructures and facilitates the potential for combining with the pump–probe methods to provide an intuitive understanding of their real‐time ionization dynamics. [ABSTRACT FROM AUTHOR]

Dynamically encircling the exceptional point (EP) of an anti‐parity‐time (anti‐PT) symmetric system can achieve chiral mode switching between symmetry‐broken eigenmodes, which is especially important for developing nanophotonic devices. However, the realization of anti‐PT‐symmetric systems on a chip still remains significantly challenging as precisely controlling the parameters of nanophotonic structures is difficult. Herein, a novel anti‐PT‐symmetric system is designed and constructed on a silicon‐on‐insulator chip by taking advantage of subwavelength gratings to help engineer nanophotonic structures. Consequently, on‐chip chiral switching between symmetry‐broken eigenmodes is experimentally realized by dynamically encircling the EP in parametric space of the proposed anti‐PT‐symmetric system. Moreover, the achieved chiral mode switching exhibits high output power ratios (≥ 6.4 dB) at 1550 nm, wide‐band response that covers C‐band completely, and great thermal stability up to 90 °C, which indicate desirable performance features for practical applications in optical communication. This study paves an avenue for realizing on‐chip chiral switching between symmetry‐broken modes, which shows great promise for developing nanophotonic devices, such as optical switching, logic gates, and isolators, in optical telecommunication bands. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMD) have attracted considerable attention in the field of photonic integrated circuits due to their giant optical anisotropy. However, on account of their inherent loss in the visible region and the difficulty of measuring high refractive index materials, near-field characterizations of the optical anisotropy of TMD in the visible region have inherent experimental difficulties. In this work, we present a systematical characterization of the optical anisotropy in tungsten disulfide (WS2) flakes by using scattering-type scanning near-field optical microscopy (s -SNOM) excited at 671 nm. Transverse-electric and transverse-magnetic (TM) waveguide modes can be excited in WS2 flakes with suitable thickness, respectively. With the assistance of the Au substrate, the contrast of the near-field fringes is enhanced in comparison with the SiO2 substrate. By combining waveguide mode near-field imaging and theoretical calculations, the in-plane and out-of-plane refractive indexes of WS2 are determined to be 4.96 and 3.01, respectively, indicating a high birefringence value up to 1.95. This work offers experimental evidence for the potential application of WS2 in optoelectronic integrated circuits in the visible region. [ABSTRACT FROM AUTHOR]

The sensitivity of strong-field ionization to atomic orbital helicity has attracted much attention from physicists, due to its potential application in attosecond spectroscopy and spintronics. In order to intuitively observe the physical mechanisms of helicity-dependent ionization rates during photoionization, the concept of the Wigner phase can be used to characterize the different interactions between the rotating electrons and the Coulomb potential. Here, we find that in both one- and three-photon ionization schemes, the electrons liberated more easily by the circularly polarized laser field suffer less influence of the Coulomb potential during the propagation and then accumulate less Winger phase. This result indicates that the strength of the interaction between the rotating electrons and the Coulomb potential can explain the helicity-dependent ionization for different ionization mechanisms universally, which is also supported by our classical ensemble analysis. Our work provides an intuitive perspective towards the physics picture of ionization propensity rules. [ABSTRACT FROM AUTHOR]

We propose a quantitative polarization-resolved quantum trajectory approach to analyse the solid high-order harmonic generation (HHG). By using this approach, we can distinguish the ionization channels of different polarization components in HHG. We take the HHG in hBN under two counter-rotating circularly polarized fields as an example. We find that the right and left circular polarized high harmonics are contributed by the electron trajectories with the ionization channel around the high symmetry points K and K ′ respectively. Furthermore, the intensity of the right and left circular polarization harmonics is determined by the interference between these electron trajectories. Our work offers a quantitatively polarization-resolved analysis to understand the underlying mechanism in HHG in the view of electron reciprocal space trajectory. [ABSTRACT FROM AUTHOR]

Coherent superposition of electronic states induces attosecond electron motion in molecules. We theoretically investigate the strong-field ionization of this superposition state by numerically solving the time-dependent Schrödinger equation. In the obtained photoelectron momentum distribution, an intriguing bifurcation structure appears in the strong-field holographic interference pattern. We demonstrate that this bifurcation structure directly provides complete information about the status of the transient wave function of the superposition state: the horizontal location of the bifurcation in the momentum distribution reveals the relative phase of the involved components of the superposition state and the vertical position indicates the relative coefficient. Thus, this bifurcation structure takes a snapshot of the transient electron wave packet of the superposition state and provides an intuitive way to monitor electron motion in molecules. [ABSTRACT FROM AUTHOR]

Interferometry, a key technique in modern precision measurements, has been used for length measurement in engineering metrology and astronomy. An analogous time-domain interferometric technique would represent a significant complement to spatial domain applications and require the manipulation of interference on extreme time and energy scales. Here, we report an all-optical interferometer using laser-driven high order harmonics as attosecond temporal slits. By controlling the phase of the temporal slits with an external field, a time domain interferometer that preserves both attosecond temporal resolution and hundreds of meV energy resolution is implemented. We apply this exceptional temporal resolution to reconstruct the waveform of an arbitrarily polarized optical pulse, and utilize the provided energy resolution to interrogate the abnormal character of the transition dipole near the Cooper minimum in argon. This novel attosecond interferometry paves the way for high precision measurements in the time-energy domain using all-optical approaches. [ABSTRACT FROM AUTHOR]

Charge migration during light–matter interaction is one of the most fundamental processes which plays a key role in chemical and biological processes of molecule. The measurement of this process requires the extreme temporal and subatomic spatial resolutions. Here, we show that a scheme based on infrared pump and short extreme ultraviolet probe technique enables us to trace the laser-controlled electron motion with high spatiotemporal resolution. By numerically solving the time-dependent Schrödinger equation for combined with a simple double-slit model, we demonstrate that the laser-controlled charge migration can be directly reconstructed from the interference patterns of the photoelectron spectrum. [ABSTRACT FROM AUTHOR]

• Low-cost fiber MI temperature sensor is formed by filling SCF with polymer-UV glue. • High sensitivity is obtained due to the great thermal properties of UV glue. • Our sensor shows advantages of robust, small size, and low cost. • The reflective tip structure enable for remote sensing in practical applications. A low-cost fiber tip temperature sensor is proposed and experimentally demonstrated. It is based on the Michelson interferometer (MI) structure which is partially filled with polymer-UV glue in the suspended core fiber (SCF). Due to the greater thermal properties of UV glue compared with the silica optical fiber, the length of the inner cavity in the MI structure is susceptible to temperature modulation, resulting in the interference wavelength drift. Experimental results show that the sensor achieves a sensitivity of −164 pm/°C in the temperature range of 25–60 °C, and the sensor offers good wavelength and power stability at room temperature. In addition, the sensor has advantages such as robust, small size, and low cost, especially the reflective tip structure is more suitable for remote sensing in practical applications. [ABSTRACT FROM AUTHOR]

• A highly-sensitive pressure sensor with sensitivity of 80.8 pm/kPa. • Low temperature cross sensitivity of 2.2 kPa/°C. • Experimental results in good agreement with the "Two-beam" interference model. • Simple fabrication technique without fiber machining, and possible for mass production. We propose and demonstrate a simple highly-sensitive gas pressure sensor based on harmonic Vernier effect. By fusion splicing two hollow silica capillaries, a cascaded Fabry-Perot (FP) cavity is formed. Without special photonics crystal fibers or laser machining involved, the fabrication process is greatly simplified. The interplay between the two interferometers consisting the FP cavity leads to optical Vernier effect. By properly adjusting the length of the silica capillaries harmonic of optical Vernier effect is observed and can be served as a sensitive probe for diagnosing gas pressure. Our results showed a sensitivity of 80.8 pm/kPa from 1 to 101 kPa with good linearity of 99.7%, and a low temperature cross sensitivity of 2.22 kPa/°C, a factor of three lower than that of the microstructure fiber-based gas pressure sensors. Combining both ease of fabrication and high sensitivity, this sensor can be a good candidate for mass production in fields of gas sensing and environmental safety monitoring. [ABSTRACT FROM AUTHOR]

We conducted a joint theoretical and experimental study to investigate the collisional dissipation of molecular alignment. By comparing experimental measurements to the quantum simulations, the nonsecular effect in the collision dissipation of molecular alignment was unveiled from the gas-density-dependent decay rates of the molecular alignment revival signals. Different from the conventional perspective that the nonsecular collisional effect rapidly fades within the initial few picoseconds following laser excitation, our simulations of the time-dependent decoherence process demonstrated that this effect can last for tens of picoseconds in the low-pressure regime. This extended timescale allows for the distinct identification of the nonsecular effect from molecular alignment signals. Our findings present the pioneering evidence that nonsecular molecular collisional dissipation can endure over an extended temporal span, challenging established concepts and strengthening our understanding of molecular dynamics within dissipative environments.

Real-time visualization of molecular transformations is a captivating yet challenging frontier of ultrafast optical science and physical chemistry. While ultrafast x-ray and electron diffraction methods can achieve the needed subangstrom spatial resolution, their temporal resolution is still limited to hundreds of femtoseconds, much longer than the few femtoseconds required to probe real-time molecular dynamics. Here, we show that high-order harmonics generated by intense femtosecond lasers can be used to image molecules with few-ten-attosecond temporal resolution and few-picometer spatial resolution. This is achieved by exploiting the sensitive dependence of molecular recombination dipole moment to the geometry of the molecule at the time of harmonic emission. In a proof-of-principle experiment, we have applied this high-harmonic structure imaging (HHSI) method to monitor the structural rearrangement in NH&#95;{3}, ND&#95;{3}, and N&#95;{2} from one to a few femtoseconds after the molecule is ionized by an intense laser. Our findings establish HHSI as an effective approach to resolve molecular dynamics with unprecedented spatiotemporal resolution, which can be extended to trace photochemical reactions in the future.

Bloch oscillations (BOs) in a parity-time (PT)-symmetric Su-Schrieffer-Heeger (SSH) waveguide array are theoretically investigated. We show that the BOs are amplified or damped even for the systems to exhibit entirely real energy bands. The amplified and damped BOs stem from the complex Berry phase and closely relate to the topological properties of the lattice. For the topological nontrivial lattice, the amplification and attenuation of BOs are much more prominent than the trivial case and the output Bloch mode can be selected. Furthermore, we propose an experimental scheme and perform a numerical simulation based on a bent waveguide array. Our work uncovers the impact of the topological properties on the dynamics of the bulk Bloch modes and unveils a horizon in the study of non-Hermitian physics. The mode selection induced by the complex Berry phase may also find application in integrated photonic devices such as the mode filter.

We investigate the non-Hermitian Hofstadter-Harper model composed of microring resonators, in which the non-Hermitian skin effect (NHSE) is particularly analyzed. The effect is achieved through the interaction between well-designed gain-loss layouts and artificial gauge fields. Remarkably, we reveal the emergence of a hybrid skin-topological effect (HSTE), where only the original topological edge modes convert to skin modes while bulk modes remain extended. By changing the distributions of gauge fields, we show the NHSE can manifest itself in bulk modes and be localized at specific edges. Using the equivalence of sites in the bulk or at boundaries to 1D SSH chains, we analyze the potential cancellation of NHSE in these configurations. Additionally, we demonstrate a new, to the best of our knowledge, type of HSTE in topological insulators which emerge at any gain-loss interfaces. The study may improve the understanding of the NHSE behavior in 2D topological systems and provide a promising avenue for tuning light propagation and localization.

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 the ultrafast dynamics is provided. Thus, a large number of theoretical studies have been proposed to understand the underlying physics of solid HHG. Here, we revisit the recollision picture in solid HHG and show some challenges of current particle-perspective methods, and present the recently developed wave-perspective Huygens-Fresnel picture for understanding dynamical systems within the ambit of strong-field physics., (Creative Commons Attribution license.)