A0472 Higher harmonic generation microscopy for rapid, label-free imaging of renal cancer tissue: Preliminary results from the INTelligent Imaging RCC (INTIMA) study

Random walks-both classical and quantum-unlocked new possibilities in search algorithms and information processing. Although linear photonic systems, with flexible tunability and multiple degrees of freedom, have served as efficient carriers for random walks, they typically require cascaded implementations, presenting a potential limitation on realizing integrated photonic circuits. In this work, we demonstrate a non-cascade, high-dimensional random walk in the orbital angular momentum (OAM) space of light using solid-state high-harmonic spectroscopy. The crystal nonlinearity enables the simultaneous conversion of multiple photons into a series of harmonics with distinct colors and whose OAM distributions are determined by the symmetry of the crystal. This approach reveals the dynamics of photonic degrees of freedom in high-harmonic generation can be naturally framed as an ultrafast, high-dimensional random walk, paving the way for compact, highly stable photonic platforms tailored for solid-state information processing.

We demonstrate extreme-ultraviolet (EUV) spectroscopic ellipsometry (SE) using a tabletop high-harmonic generation (HHG) source for optical-constant determination. The polarization-resolved system enables accurate retrieval of the complex refractive index n-ik, as validated by measurements on a Nb2O5 film and by indirect determination of the optical constants of molybdenum and gold mirrors in the analyzer. This approach provides a compact and versatile platform for precise EUV optical-constant determination and future ultrafast studies.

Sky-high optical nonlinearities make semiconductors ideal platforms for multifunctional photonic devices. The fabrication of such complex devices could greatly benefit from in-volume ultrafast laser writing for monolithic and contactless integration. Ironically, as exemplified for Si, nonlinearities act as an efficient immune system that self-protects the material from internal permanent modifications. Predicting high-intensity ultrashort-pulse propagation beyond Si is further limited by incomplete descriptions of carrier dynamics in narrow-gap materials. Here, we demonstrate that filamentation universally dictates ultrashort laser pulse propagation in various semiconductors. The effective key nonlinear parameters extracted differ markedly from past measurements with low-intensity pulses, while temporal scaling laws for these parameters are also derived. Based on these findings, appropriate temporal-spectral shaping is proposed for tailored energy deposition inside semiconductors. The effective parameters also provide predictive inputs for semiconductor backside processing, microelectronics security, and high-harmonic, supercontinuum and terahertz wave generation.

High harmonic generation by dynamic Fermi surface nesting

Abstract High harmonic generation (HHG) provides an experimental method for producing attosecond pulses and probing electron dynamics. Precise dipole phase measurement, critical for tailoring harmonic emission phase and identifying HHG mechanism, remains challenging in traditional two-beam far-field interferometry when applied to solid materials. In this study, we present a novel interferometric approach that utilizes a single laser beam to simultaneously excite two ZnO microwires (MWs), thereby generating coherent high-harmonic sources that form interference fringes in the far-field region. By exploiting the diameter-dependent field enhancement effect in MWs, the measured intensity-dependent fringe shift reveals that the intraband current mechanism dominates the below-bandgap harmonic, and the interband polarization mechanism dominates the above-bandgap harmonic. This study offers a robust method for measuring the dipole phase of solid-state HHG and inspires intensity-modulated high-harmonic applications in coherent imaging and microdevice design.

Abstract Time-resolved photoelectron spectroscopy is a powerful approach for probing transient surface morphology and ultrafast carrier dynamics in solids. Quantitative analysis of non-equilibrium dynamics requires stable light source with easy geometry and less space charging effect. Here we report a high-repetition-rate extreme-ultraviolet (XUV) pulses based on high-harmonic generation (HHG), designed to support state-of-the-art momentum microscopy (MM) for imaging ultrafast electron dynamics in both real and reciprocal space. The XUV source with an improved differential gas jet operates at 100 kHz repetition rate with central photon energy of 21.6 eV, spectral width of 110 meV, and the maximum photon flux of 3 × 10 10 photonsss (single-harmonic selection) delivered to the sample. The flux of single HHG is 1.5 times than that generated with a regular gas jet. Interferometry characterization of the gas density distribution in the differential gas jet reveals the influence of skimmer parameters on gas density profile, exerting a further notable influence on the HHG flux. By employing appropriate skimmers, the gas density can be capable of mitigating the decrease in gas density with increasing distance, enhancing the gas density at relatively far positions, and eventually enhance the harmonic flux. These results give important guiding significance for gas field manipulation in gas-distribution-sensitive light-matter interaction experiments.

Abstract We present a high‑power Yb‑fiber chirped‑pulse amplification (CPA) system incorporating a chirped fiber Bragg grating for passive spectral pre‑shaping. The compact double‑pass CPA system delivers 414-µJ, 270-fs pulses at 250 kHz (103.5-W average power) with a net gain of 39.3 dB. To further shorten the pulse duration, a multi‑pass cell (MPC) is employed for nonlinear post‑compression, achieving 35-fs pulses with ~95% throughput efficiency and 98-W average power. This double-pass CPA system equipped with high‑efficient MPC post‑compression offers a scalable and robust route to high‑energy ultrafast driving sources for high-harmonic generation.

Molecular high-harmonic generation under the influence of a significant dipole moment

The paper investigates ultrasonic nonlinear shear horizontal waves. The major focus of the work undertaken is on the fundamental mode due to its non-dispersive nature. Nonlinear crack-wave interaction is investigated. Local crack-induced nonlinear elasticity and dissipation are modelled using hysteresis. Numerical simulations of crack-wave interaction are performed using the Local Interaction Simulation Approach, allowing not only for top-down solution of nonlinear differential equations but potentially also for parallel computing architecture. Modelling and numerical simulations are undertaken to reveal various nonlinear phenomena. This includes not only higher harmonic generation but also nonlinear vibro-acoustic modulations. Numerical simulations demonstrate that cracks can be effectively represented using local models of hysteresis that have been previously used for modelling of distributed material nonlinearity.

High harmonic generation and wave mixing in graphene quantum dots by bichromatic laser fields of circular polarization

Design, synthesis and characterization of a novel chalcone derivative crystal with high second harmonic generation efficiency

High harmonic generation in solids driven by optical skyrmions

High-harmonic generation (HHG) is used as a source for various imaging applications in the extreme ultraviolet spectral range. It offers spatially coherent radiation and unique elemental contrast with the potential for attosecond time resolution. The unfavorable efficiency scaling to higher photon energies prevented the imaging application in the soft X-ray range so far. In this work we demonstrate the feasibility of using harmonics for imaging in the water window spectral region (284 eV to 532 eV). We achieve nondestructive depth profile imaging in a heterostructure by utilizing a broadband and noise-resistant technique called soft X-ray Coherence Tomography (SXCT) at a high-flux lab-scale HHG source. SXCT is derived from Optical Coherence Tomography, a Fourier based technique that can use the full bandwidth of the source to reach an axial resolution of 12 nm in this demonstration. The employed source covers the entire water window, with a photon flux exceeding 106 photons/eV/s at a photon energy of 500 eV. We show local cross sections of a sample consisting of Aluminium oxide and Platinum layers of varying thickness on a Zinc oxide substrate. We validate the findings with scanning and transmission electron microscopy after preparation with focused ion beam milling.

Attosecond-pump attosecond-probe spectroscopy (APAP) is the key to understanding electronic-dominated dynamics in light-matter interactions. Although the feasibility of APAP has been demonstrated using isolated attosecond pulses (IAPs), the efforts are mainly confined to the ionization-induced dynamics triggered by the extreme ultraviolet and soft x-ray lights. However, the generation of IAPs capable of exciting neutral electronic excited states, which are more prevalent in nature, is still in its infancy, significantly limiting comprehensive insights into valence-electron wave packet dynamics. Here, we theoretically demonstrate a scheme for the straightforward and compact generation of white-light IAPs covering the visible and ultraviolet regions, based on solid-state high-harmonic generation. By analyzing the strong-field-induced electron-hole dynamics together with a saddle-point approximation, we unfold its microscopic generation mechanism. Furthermore, the feasibility and robustness of this approach are validated by the generation of IAPs from various materials under the same mechanism. Our work paves the way for generation of tabletop white-light IAP sources, thereby harnessing the widespread applications of APAP.

High harmonic generation(HHG) is a powerful probe ofelectrondynamics on attosecond to femtosecond time scales and has been successfullyused to detect electronic and structural changes in solid-state quantummaterials, including transition-metal dichalcogenides (TMDs). AmongTMDs, bulk NbSe2 exhibits charge density wave (CDW) orderbelow 33 K and becomes superconducting below 7.3 K. Monolayer NbSe2 also has superconducting and CDW behavior and is thereforeinteresting as a material whose different structural and electronicproperties could be probed via HHG. Here, we predict the HHG responseof the pristine 2H and CDW phases of monolayer NbSe2 usingreal-time time-dependent density functional theory under the applicationof a simulated laser pulse excitation. We find that due to the lackof inversion symmetry in both monolayer phases, it is possible toexcite even harmonics and that the even harmonics appear as the transversecomponents of the current response under excitations polarized alongthe zigzag direction of the monolayer, while odd harmonics arise fromthe longitudinal current response in all excitation directions. Thissuggests that the even and odd harmonic responses can be controlledvia the polarization of the probing field, opening an avenue for potentiallyuseful applications in optoelectronic devices.

High-harmonic generation has been established in gases both as a source of extreme ultraviolet light as well as a tool for studying atomic and molecular physics in the attosecond time domain. The more recent extension of these methods to condensed matter affords much higher conversion efficiencies and offers an even richer selection of accessible phenomena. Atomically thin two-dimensional semiconductors combine mechanical robustness with intriguing many-body physics and exceptionally strong light-matter interaction. This mini-review gives a glance into the high-harmonic generation mechanisms in two-dimensional semiconductors, with particular emphasis on symmetry considerations, many-body effects, photodoping, and techniques to further enhance the high-harmonic generation efficiency.

Abstract In this paper, we studied the transformation of light in a rhombus graphene quantum dot during the generation of high harmonics in an intense laser field of elliptical polarization. The linearly polarized laser field leads to intense emission of elliptically polarized harmonics and vice versa. The ellipticity and orientation of the polarization ellipse are derived from the Stokes parameters calculated by considering various polarization components. Numerical results show that the ellipticity of harmonics generated in a quantum dot can be easily tuned by adjusting the tilt angle of the polarization vector of the elliptically polarized laser pulse, eliminating the need for complex control systems.

Attosecond Waveform Engineering via Spectral-Temporal Coupled High Harmonic Generation

High-harmonic generation in a metasurface