arXiv subjects

T. Brabec

Publications and source records attributed to T. Brabec.

7 recordsLinked to original sources

arXiv2023

Orbital perspective on high-harmonic generation from solids

High-harmonic generation in solids allows probing and controlling electron dynamics in crystals on few femtosecond timescales, paving the way to lightwave electronics. In the spatial domain, recent advances in the real-space interpretation of high-harmonic emission in solids allows imaging the field-free, static, potential of the valence electrons with picometer resolution. The combination of such extreme spatial and temporal resolutions to measure and control strong-field dynamics in solids at the atomic scale is poised to unlock a new frontier of lightwave electronics. Here, we report a strong intensity-dependent anisotropy in the high-harmonic generation from ReS$_2$ that we attribute to angle-dependent interference of currents from the different atoms in the unit cell. Furthermore, we demonstrate how the laser parameters control the relative contribution of these atoms to the high-harmonic emission. Our findings provide an unprecedented atomic perspective on strong-field dynamics in crystals and suggest that crystals with a large number of atoms in the unit cell are not necessarily more efficient harmonic emitters than those with fewer atoms.

physics.optics↗

arXiv2022

Mechanisms of high harmonic generation in solids

The long standing issue of separating resonant from non-resonant processes in extreme nonlinear optics is resolved. The theoretical formalism is applied to high harmonic generation (HHG) in solids and reveals a deeper view into the dominant laser and material dependent mechanisms. Mid-infrared driven HHG in semiconductors is dominated by the resonant interband current. As a result of the dynamic Stark shift, virtual processes gain in importance in near-infrared driven HHG in dielectrics. Finally, our analysis identifies limitations of microscopic one-electron-hole theories.

physics.optics↗

arXiv2018

High harmonic generation tomography of impurities in solids: conceptual analysis

A three step model for high harmonic generation from impurities in solids is developed. The process is found to be similar to high harmonic generation in atomic and molecular gases with the main difference coming from the non-parabolic nature of the bands. This opens a new avenue for strong field atomic and molecular physics in the condensed matter phase. As a first application, our conceptual study demonstrates the feasibility of tomographic measurement of impurity orbitals.

physics.atom-ph↗

arXiv2017

Theory of Kerr Instability Amplification

A new amplification method based on the optical Kerr instability is suggested and theoretically analyzed, with emphasis on the near to mid-infrared wavelength regime. Our analysis for CaF2 and KBr crystals shows that one to two cycle pulse amplification by 3-4 orders of magnitude in the wavelength range from 1-14 microns is feasible with currently available laser sources. At 14 microns final output energies in the 0.05 mJ range are achievable corresponding to about 0.2-0.25% of the pump energy. The Kerr instability presents a promising process for the amplification of ultrashort mid-infrared pulses.

physics.optics↗

arXiv2010

Steplike intensity threshold behavior of extreme ionization in laser-driven Xe clusters

The generation of highly charged Xe$^{q+}$ ions up to {$q=24$} is observed in Xe clusters embedded in helium nanodroplets and exposed to intense femtosecond laser pulses ($λ$=800 nm). Laser intensity resolved measurements show that the high-$q$ ion generation starts at an unexpectedly low threshold intensity of about {10$^{14}$ W/cm$^{2}$}. Above threshold, the Xe ion charge spectrum saturates quickly and changes only weakly for higher laser intensities. Good agreement between these observations and a molecular dynamics analysis allows us to identify the mechanisms responsible for the highly charged ion production and the surprising intensity threshold behavior of the ionization process.

physics.atm-clus↗

arXiv2006

Tunnel ionization of open-shell atoms

A generalized ADK (Ammosov-Delone-Krainov) theory for ionization of open shell atoms is compared to ionization experiments performed on the transition metal atoms V, Ni, Pd, Ta, and Nb. Our theory is found to be in good agreement for V, Ni, Pd, and Ta, whereas conventional ADK theory overestimates ionization by orders of magnitude. The key to understanding the observed ionization reduction is the angular momentum barrier. Our analysis shows that the determination of the angular momentum barrier in open shell atoms is nontrivial. The Stark shift is identified as the second dominant effect responsible for ionization suppression. Finally, these two effects cannot explain the Nb data. An analysis of the electron spins suggests that Pauli blocking might be responsible for the suppression of tunneling in Nb.

physics.atom-ph↗

arXiv2005

Plasmon signatures in high harmonic generation

High harmonic generation in polarizable multi-electron systems is investigated in the framework of multi-configuration time-dependent Hartree-Fock. The harmonic spectra exhibit two cut offs. The first cut off is in agreement with the well established, single active electron cut off law. The second cut off presents a signature of multi-electron dynamics. The strong laser field excites non-linear plasmon oscillations. Electrons that are ionized from one of the multi-plasmon states and recombine to the ground state gain additional energy, thereby creating the second plateau.

quant-ph↗