High-harmonic generation from a gas target exhibits sharp spectral features and rapid phase variation near the Cooper minimum. By applying filtering, shaped isolated attosecond pulses can be generated where pulse is split into two in time domain. Using such extreme-ultraviolet (XUV) pulses, we theoretically study transient absorption (ATA) spectra of helium <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn...

Through high-order harmonic generation driven by intense ultrashort vortex infrared or midinfrared lasers, a nonzero orbital angular momentum can be imprinted onto extreme ultraviolet (XUV) soft-x-ray (SXR) light pulses. Here we simulate the of XUV harmonics in gas medium as well their propagation vacuum till reaching far field. We find that intensity and phase generated high are very sensitive to position jet with respect laser focus. The topological charge $q\mathrm{th}$ is found $q$ times...

We identify optimal conditions for the generation and isolation of attosecond pulses in an overdriven ionized medium. In a high-pressure highly gas, spatiotemporal wavefront rotation driving laser can be optimized, leading to complete spatial separation successive bursts far field. The resulting isolated (IAPs) are much more divergent such that they spatially separated from show time delay near-field harmonic emission along radial distance determines divergence burst generated IAPs phase...

Isolated attosecond pulses (IAPs) in the soft-x-ray (SXR) region have been successfully produced via high-order harmonic generation a gas medium at several laboratories, but pulse energies are much lower compared to IAPs extreme ultraviolet. Here, we show that gas-filled hollow waveguide, an efficient gating method using few-cycle three-color synthesizer is able generate stronger SXR IAPs. We 104-as IAP (central energy of 210 eV) with higher (0.9 nJ) and divergence (within 1.5 mrad) can be...

The concept of critical ionization fraction has been essential for high-harmonic generation, because it dictates the maximum driving laser intensity while preserving phase matching harmonics. In this work, we reveal a second, nonadiabatic fraction, which substantially extends phase-matched harmonic energy, arising strong reshaping intense field in gas plasma. We validate understanding through systematic comparison between experiment and theory wide range conditions. particular, properties...

Abstract Isolated attosecond pulses (IAPs) in the soft x-ray (SXR) region are highly desirable for time-resolved experiments. Here we identify a transient phase matching gating method generation of such IAPs with mid-infrared (MIR) lasers. This works when loosely focused, long-duration MIR Gaussian driving beam is slightly reshaped during its propagation gas medium under ‘critical’ ionization condition. Quantitatively, calculated coherence length high harmonic used to analyze mechanism...

Chromatic aberration occurs when high-order harmonic generation (HHG) is focused far away from its medium, exhibiting as the focal point being shifted with order, which becomes an obstacle for HHG a powerful table-top light source. Here, we demonstrate through simulations that chromatic can be efficiently corrected by using flat-top beam driving laser, induced plasma laser propagates in gas medium. We show elimination of robust gas-filled waveguide under proper pressure and length. reveal...

High-order harmonics have been widely used as reliable tabletop coherent radiation sources recently, but their applications often limited by the available pulse energy. Here, we report that using an overdriven intense laser in a long waveguide with high-pressure gas, phase matching can be achieved three distinct "regimes". In third regime, favorable is at near-axis positions to enhance harmonic yields. Our results are supported full theoretical analysis, and demonstrate coupling of driving...

We propose to correct the ionization factor in quantitative rescattering (QRS) theory for a higher precision calculation of macroscopic high harmonic generation (HHG) gaseous medium. Compared first-order strong-field approximation (SFA-1) and Ammosov-Delone-Krainov (ADK) models, Perelomov-Popov-Terent'ev (PPT) model achieves best agreement with HHG spectra Ar based on solution time-dependent Schr\"odinger equation (TDSE). The investigation probability dependence laser intensity indicates...

We study high-order harmonic generation (HHG) with an annularly shaped high-power, high-repetition-rate laser. investigate how the spatial separation (or divergence) of incident laser and generated harmonics depends on gas pressure when intensity is in overdriven regime. It shown that, cone size annular beam relatively large, resulting are highly collimated along propagation axis spatially separated from beam. Under condition, dynamic phase matching favors HHG emissions short-trajectory...

Using genetic algorithm, we propose a method to retrieve the alignment distribution of transiently aligned ${\mathrm{CO}}_{2}$ molecules from high-order harmonic generation (HHG) spectra. The retrieval is based on quantitative rescattering (QRS) model where averaged photorecombination transition dipole can be factored out parallel (or perpendicular) spectra after propagation fields in gas medium. We examine how retrieved distributions are affected by uncertainty alignment-dependent...

We investigate the generation of near-threshold harmonics (NTHs) based on solving three-dimensional time-dependent Schr\"odinger equation and utilizing an artificial neural network as a surrogate model to study macroscopic propagation. Through our research, we identify two distinct pathways for NTH generation: harmoniclike transition resonant transition. These exhibit varying laser-parameter dependencies phase-matching conditions, making it possible spatially separate selectively enhance...

Nonadiabatic phase matching of high-harmonic generation (HHG) driven by few-cycle laser pulses is essential for extending harmonic energy and generating isolated attosecond pulses. However, understanding nonadiabatic HHG challenging due to the complex interplay various optical phases temporally spatially varying fields. Theoretical calculations typically rely on computationally demanding 3-dimensional simulations, which can make it difficult extract features HHG. In this work, we develop a...

We theoretically investigate the modulated high-harmonic generation (HHG) driven by an intense few-cycle infrared (IR) laser field and a weak extreme-ultraviolet (XUV) pulse at delayed time. establish extended quantitative rescattering (EQRS) model to simulate HHG streaking spectra, with ideas of correcting IR ionization transition from ground continuum states in strong-field approximation. The EQRS has accuracy comparable that ``exactly'' solving time-dependent Schr\"odinger equation...

An all-optical method for directly reconstructing the spectral phase of an isolated attosecond pulse (IAP) has been proposed recently [New J. Phys. 25, 083003 (2023)]. This is based on high-harmonic-generation (HHG) streaking spectra generated by IAP and a time-delayed intense infrared (IR) laser, which can be accurately simulated extended quantitative rescattering model. Here, we extend retrieval algorithm in this to successfully retrieve shaped IAP, minimum, jump about $\ensuremath{\pi}$,...

Isolated attosecond pulses (IAPs) can be readily generated via high-order harmonic generation driven by an ultrashort laser pulse. Here, it is shown that the best way to obtain waveform for producing a short and intense IAP in soft x rays optimize three-color (TC) pulse consisting of fundamental field its second third fields. To calibrate it, another constructing directly time using truncated basis set B-spline functions first proposed. The calibration (CW) contains more frequency components...

The nickel molybdate carbon nanotube composites [Formula: see text] were synthesized by solution blending method. characterized scanning electron microscopy (SEM), Raman spectroscopy and UV–Vis absorption spectroscopy. organic glasses obtained dispersing in methyl methacrylate (MMA) polymerizing a water bath at for 1[Formula: text]h. nonlinear optical (NLO) properties measured via text]-scan technique. By testing we that has reverse saturation (RSA) effect limiting (OL) performance. In...