Phase-matching mechanism for high-harmonic generation in the overdriven regime driven by few-cycle laser pulses

Abstract

Isolated attosecond pulses (IAPs) produced through laser-driven high-harmonic generation (HHG) hold promise for unprecedented insight into biological processes via attosecond x-ray diffraction with tabletop sources. However, efficient scaling of HHG towards x-ray energies has been hampered by ionization-induced plasma generation impeding the coherent buildup of high-harmonic radiation. Recently, it has been shown that these limitations can be overcome in the so-called 'overdriven regime' where ionization loss and plasma dispersion strongly modify the driving laser pulse over small distances, albeit without demonstrating IAPs. Here, we report on experiments comparing the generation of IAPs in argon and neon at 80 eV via attosecond streaking measurements. Contrasting our experimental results with numerical simulations, we conclude that IAPs in argon are generated through ionization-induced transient phase-matching gating effective over distances on the order of 100 $\mu$m. We show that the decay of the intensity and blue-shift due to plasma defocussing are crucial for allowing phase-matching close to the XUV cutoff at high plasma densities. We perform simulations for different gases and wavelengths and show that the mechanism is important for the phase-matching of long-wavelength, tightly-focused laser beams in high-pressure gas targets, which are currently being employed for scaling isolated attosecond pulse generation to x-ray photon energies.

arXiv comment22 pages, 13 figures

References in corpus (6)

• Bright Coherent Ultrahigh Harmonics in the keV X-Ray Regime from Mid-Infrared Femtosecond Lasers
• Phase matching of high harmonic generation in the soft and hard X-ray regions of the spectrum
• 0.5 keV soft X-ray attosecond continua
• Phase-Matching of High-Order Harmonics Driven by Mid- Infrared Light
• Generation of Bright Isolated Attosecond Soft X-Ray Pulses Driven by Multi-Cycle Mid-Infrared Lasers
• Ptychographic reconstruction of attosecond pulses

Cited by in corpus (7)

• Lightwave-controlled band engineering in quantum materials
• Extension of the bright high-harmonic photon energy range via nonadiabatic critical phase matching
• High-harmonic generation in a strongly overdriven regime
• Extended model for optimizing high-order harmonic generation in absorbing gases
• The emergence of macroscopic currents in photoconductive sampling of optical fields
• Time Resolved Investigation of High Repetition Rate Gas Jet Target For High Harmonic Generation
• Tuning the electronic band structure of metal surfaces for enhancing high-order harmonic generation